Aqa C2 Revision Booklet l5234
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GCSE ADDITIONAL CHEMISTRY (C2) REVISION BOOKLET Name ________________________ These are summary questions for all topics in the GCSE Chemistry exam. When you have completed the booklet go to the school’s website, find the relevant mark scheme and mark your work. Check off each section and enter your score. If you find a section(s) produce low scores you can: Come to catch up and ask for help Go online: o http://www.bbc.co.uk/schools/bitesize/ o http://www.s-cool.co.uk/ o http://web.aqa.org.uk/qual/newgcses/science/new/bio_mate rials.php?id=03&prev=03 Use your notes and revision guides You can purchase revision guides from Mrs Fuller in the main science prep room. All the above will identify areas of weakness and give you strategies to swat up on.
Score Date C2.1 Structures and Bonding
___ / 33
C2.2 Structures and Properties C2.3 How much?
___ / 37 ___/ 39
C2.4 Rates of Reaction
___ / 36
C2.5 Energy and Reactions
___ / 32
C2.6 Electrolysis
___/ 47
C2.7 Acids, Alkalis and Salts
___/ 46
End of unit exam
___/ 46
S Williams Nov ‘10
Grade %
90+ 80
A* A
70 60 50 40 30 20
B C D E F G
C2.1 Structures and bonding Name:
Date:
Summary questions Fill in the gaps in the following sentences to test your recall of the facts you have learned in this chapter. 1
a) The centre of an atom is called the ........................................... . b) In the centre of the atom there are two types of sub-atomic particles. These particles are the ........................ and the ........................... . The ............................ are positively charged. The ........................ have no charge. They are neutral. c) The centre of the atom is .................................. charged. This is because of the positively charged sub-atomic particles called ..................... . d) Around the centre are negatively charged sub-atomic particles called .................... . e) The overall charge on an atom is zero. Therefore the number of .............................. and .......................... are equal. f)
The electrons are arranged in energy ........................ around the centre of the atom.
g) The first energy ...................... is nearest to the centre and can take a maximum of ................ electrons. h) The second and third energy .......................... can take a maximum of .................... electrons each. i)
The first .................... level is filled with electrons first and then the ...................... and third ones.
j)
When atoms bond with other atoms, the number of .................... in their outermost energy .................... changes.
2
a) In ionic bonding, electrons from one atom are .............................. to another. b) The charged particles formed are called .................. . c) Negative ions are formed when atoms .................... electrons. d) Positive ions are formed when atoms .................... electrons. e) An example of an ionic compound is ........................ chloride. f)
............................ bonds are formed when pairs of electrons are .................... between atoms.
g) An example of a .............................. substance is water. h) Diamond is an example of a ..................... covalent substance. i)
Dots and .................... represent the electrons in these two types of bonding.
j)
In metals the positively charged metal .............. are arranged in ........................ .
k) The .......................... of metal ions are in a ................ of free .............................. .
Total = ___/33 AQA Science © Nelson Thornes Ltd 2006
C2 1
1
Student Answer Booklet CHEMISTRY C2.1 Structures and Bonding Answers to summary questions 1 a) The centre of an atom is called the nucleus. b) In the centre of the atom there are two types of sub-atomic particles. These particles are the proton and the neutron. The protons are positively charged. The neutrons have no charge. They are neutral. c) The centre of the atom is positively charged. This is because of the positively charged sub-atomic particles called protons. d) Around the centre are negatively charged sub-atomic particles called electrons. e) The overall charge on an atom is zero. Therefore the number of electrons and protons are equal. f) The electrons are arranged in energy levels around the centre of the atom. g) The first energy level is nearest to the centre and can take a maximum of two electrons. h) The second and third energy levels can take a maximum of eight electrons each. i) The first level is filled with electrons first and then the second and third ones. j) When atoms bond with other atoms, the number of electrons in their outermost energy level changes. 2 a) In ionic bonding, electrons from one atom are transferred/given to another. b) The charged particles formed are called ions. c) Negative ions are formed when atoms gain electrons. d) Positive ions are formed when atoms lose electrons. e) An example of an ionic compound is sodium/calcium/magnesium/potassium etc. chloride. f) Covalent bonds are formed when pairs of electrons are shared between atoms. g) An example of a covalent substance is water. h) Diamond is an example of a giant covalent substance. i) Dots and crosses represent the electrons in these two types of bonding. j) In metals the positively charged metal ions/cations are arranged in layers. k) The layers of metal ions are in a sea of free electrons.
1 mark for each word in bold Total = 33 marks
AQA Science © Nelson Thornes Ltd 2006
C2 1
1
C2.2 Structures and properties Name:
Date:
Summary questions Answer the following questions to test your recall and understanding of what you have learned in this chapter. 1
2
Decide which of these statements are true and which are false. a) Ionic compounds have high melting points.
True/false
b) This is because the bonds between the molecules present are strong.
True/false
c) Ionic compounds conduct electricity in the solid state.
True/false
d) In solid ionic compounds the ions can move and carry the current.
True/false
e) Covalently bonded compounds tend to have low melting and boiling points.
True/false
f)
True/false
Intermolecular forces are strong and make it difficult to separate the molecules.
g) Diamond and graphite are also simple covalent molecules.
True/false
h) Covalent substances do not conduct electricity.
True/false
i)
Graphite conducts electricity.
True/false
j)
Graphite is slippery because the bonds between the atoms are weak covalent bonds. True/false
In this question, cross out the wrong alternatives. Ionic compounds have low/high melting points because the forces of attraction between the ions/molecules are strong. When they are in solid/liquid form, ionic compounds are poor electrical conductors because the ions/electrons are free/unable to move and carry the electrical current. Covalent substances tend to be good/poor electrical conductors because the ions/electrons are free/unable to move. Graphite/diamond is an exception because it has ions/electrons which are free/unable to move and carry the electrical current. Graphite/diamond is the hardest natural substance known because all its bonds are strong/weak covalent bonds. Graphite/diamond is a very slippery substance because the bonds between/inside the layers of carbon atoms are weak/strong and easily broken so the layers can slide over each other easily. Metals are good/poor electrical conductors because the ions/electrons are free/unable to move and carry the electrical current. These free electrons/ions are able to move in both the liquid and solid forms. The free electrons/ions hold the metal lattice together. Metals are malleable/brittle because the layers can/cannot slide over each other. This is because as the distortion to the metal lattice occurs, the electrons/ions can also move and hold the metal molecules/ions together. Nanoparticles are very small/large particles that have properties different from/the same as the substances when they are in bulk form.
AQA Science © Nelson Thornes Ltd 2006
1 mark each = ___/37 C2 2
1
C2 2 Exam-style questions Continued …
AQA Science © Nelson Thornes Ltd 2006
C2 2
2
C2.2 Structures and Properties
Answers to summary questions 1 a) True. Ionic bonds are strong. b) False. Ionic compounds are not made up of molecules they are made up of ions. c) False. They conduct electricity in the liquid state but not the solid state. d) False. They are in fixed positions and cannot move. e) True. Covalently bonded compounds tend to have low melting and boiling points. f) False. The intermolecular forces are weak and this is why the boiling points are low. g) False. They are giant covalent molecular substances. h) True. They have no free electrons or ions (apart from graphite). i) True. It has free electrons. j) False. It is slippery but the reason given is wrong. The layers of atoms are held together by weak intermolecular forces called van der Waals forces. 2 The correct answers are in bold. Ionic compounds have high melting points because the forces of attraction between the ions are strong. When they are in solid form, ionic compounds are poor electrical conductors because the ions are unable to move and carry the electrical current. Covalent substances tend to be poor electrical conductors because the electrons are unable to move. Graphite is an exception because it has electrons which are free to move and carry the electrical current. Diamond is the hardest natural substance known because all its bonds are strong covalent bonds. Graphite is a very slippery substance because the bonds between the layers of carbon atoms are weak and easily broken so the layers can slide over each other easily. Metals are good electrical conductors because the electrons are free to move and carry the electrical current. These free electrons are able to move in both the liquid and solid forms. The free electrons hold the metal lattice together. Metals are malleable because the layers can slide over each other. This is because as the distortion to the metal lattice occurs, the electrons can also move and hold the metal ions together. Nanoparticles are very small particles that have properties different from the substances when they are in bulk form.
1 mark each = 37 marks
AQA Science © Nelson Thornes Ltd 2006
C2 2
1
C2.3 How much? Summary sheet Name:
Class:
Summary questions Answer the following questions to test your recall and understanding of what you have learned in this chapter. 1
a) What is the name given to atoms of the same element which have different mass numbers? .................................................................................................................................................. b) These atoms have different numbers of which sub-atomic particle? .................................................................................................................................................. c) In the periodic table which two properties of an element are usually given as numbers? .................................................................................................................................................. d) How is the formula mass of a compound calculated? .................................................................................................................................................. .................................................................................................................................................. .................................................................................................................................................. e) The relative atomic mass of carbon-12 expressed in grams is called a ………………… of carbon atoms. f)
In the reaction below, 1 mol of oxygen molecules reacts with how many moles of magnesium atoms? 2Mg + O2 2MgO ..................................................................................................................................................
g) What is the relative formula mass of MgO?
[relative atomic masses: Mg = 24; O = 16]
.................................................................................................................................................. .................................................................................................................................................. h) If 92 g of sodium react with 32 g of oxygen. What is the empirical formula of the compound formed?
[relative atomic masses: Na = 23; O = 16] [Higher]
.................................................................................................................................................. .................................................................................................................................................. ..................................................................................................................................................
AQA Science © Nelson Thornes Ltd 2006
C2 3
1
C2 3 Summary sheet Continued … 2
a) Balance the following equations. i)
[Higher]
….Mg + ….CO2 ….MgO + ….C
ii) ….Fe
+ ….Cl2 ……FeCl3
iii) ….N2
+ ….H2
….NH3
iv) ….Al
+ ….O2
……Al2O3
v) ….NH3 + ….CuO ….Cu + ….N2 + …..H2O b) In the reaction below what mass of fluorine will react exactly with 120 g of magnesium? Mg + F2 MgF2
[relative atomic masses Mg = 24; F = 19] [Higher]
.................................................................................................................................................. .................................................................................................................................................. .................................................................................................................................................. .................................................................................................................................................. c) When the experiment in b) was done what mass of magnesium fluoride would you expect to be formed?
[Higher]
.................................................................................................................................................. d) What is the percentage yield if 248 g of magnesium fluoride was actually formed?
[Higher]
.................................................................................................................................................. .................................................................................................................................................. e) What is a reversible reaction? .................................................................................................................................................. f)
What symbol represents a reversible reaction? .........................................................................
g) What can you say about the forward and backward reaction if a reversible reaction when equilibrium is reached? .................................................................................................................................................. 3
a) What industrial process is used to make ammonia? .................................................................................................................................................. b) What are the conditions for making ammonia? .................................................................................................................................................. c) Give a major use of ammonia. .................................................................................................................................................. d) Give one major environmental drawback of this use. ..................................................................................................................................................
AQA Science © Nelson Thornes Ltd 2006
Total = ___/39
C2 3
2
C2.3 How much? Summary sheet Teacher notes
Answers to summary questions Answers 1 a) b) c) d) e) f) g) h)
Isotopes. (1 mark) Neutrons. (1 mark) Atomic or proton number and relative atomic mass or mass number. (2 marks) By adding up the relative atomic masses of the atoms present. (1 mark) Mole. (1 mark) 2 mol of magnesium atoms react with one mole of oxygen molecules. (1 mark) 24 + 16 = 40 (1 mark) Sodium Oxygen [Higher] 92 g 32 g 92 32 mol mol (1 mark) 23 16 4 mol of sodium combine with 2 mol of oxygen. (1 mark) 2 mol of sodium combine with 1 mol of oxygen. (1 mark) formula is Na2O (3 marks total)
2 a) i) 2Mg + CO2 2MgO + C [Higher] ii) 2Fe + 3Cl2 2FeCl3 [Higher] iii) N2 + 3H2 2NH3 [Higher] iv) 4Al + 3O2 2Al2O3 [Higher] or 2Al + 1½O2 Al2O3 [Higher] v) 2NH3 + 3CuO 3Cu + N2 + 3H2O [Higher] b) There are two ways of answering this. [Higher] i) 120 g =
(2 marks) (2 marks) (2 marks) (2 marks) (2 marks) (2 marks)
120 mol of Mg 24
From the equation, 1 mol of Mg reacts with 1 mol of F2 5 mol of Mg react with 5 mol of F2 5 mol of F2 = 5 (2 19) = 190 g ii) From the equation, 24 g of Mg react with 38 g of F2 38 1 g of Mg reacts with g of F2 24 38 120 g of magnesium react with 120 g of F2 = 190 g 24 c) 190 + 120 = 310 g 248 d) Yield = 100% = 80% [Higher] 310 e) A reaction that can go both ways/backwards and forwards. f) ⇌ g) They have the same rate. 3 a) b) c) d)
(2 marks) (2 marks) (2 marks) (2 marks) (1 mark) (1 mark)
Haber. (1 mark) 250 atmospheres, 450 C and an iron catalyst. (3 marks) Fertilisers. (1 mark) Eutrophication – they cause algal blooms when they leech into rivers and lakes. (1 mark)
AQA Science © Nelson Thornes Ltd 2006
Total = 39 marks
C2 3
1
C2.4 Rates of reaction Summary sheet Name:
Class:
Summary questions Fill in the gaps in the following paragraphs to test your understanding of this chapter. 1
The rate of a chemical reaction can be found by measuring how ........................ the reactants are ............................ or how quickly the products are ....................... . An example of a chemical reaction is the reaction between calcium carbonate and hydrochloric acid: CaCO3(s) + 2HCl(aq) CaCl2(aq) + H2O(l) + CO2(g) We could measure the rate of this reaction by measuring the ..................... of the reaction mixture using a top-pan balance. Because .............................. ........................... gas is given off, the mass will ............................... . To see how quickly the reaction is taking place we plot .............. in mass (vertical axis) against ................. (horizontal axis). The steeper the line obtained, the .................... the reaction. We could also measure how quickly the gas is given off by measuring its volume using a gas ..................... . In the reaction between sodium thiosulphate and hydrochloric acid, solid sulphur is formed. This makes the reaction mixture ........................... and makes it more difficult to see ....................... the mixture. Eventually we cannot see .......................... the mixture at all and a ................................... underneath it is .......................... . We can measure the .................... it takes to do this.
2
There are four main factors that affect the rate of reaction. These are: a) ......................... . This is a measure of how crowded the particles are in a solution and the frequencies of ........................ . b) ........................ ......................... . This is a measure of how much solid is exposed to reaction and therefore how many ............................... take place. c) ......................... . This affects the energy of the particles and how quickly they ...................... . It also affects the ................... with which the particles collide and how .............................. the collisions are. The energy required for any reaction to take place is called the ......................... energy for that reaction. d) The presence of a ............................ . A ...................... will speed up a chemical reaction but is ............................. chemically and weighs the same at the end of the reaction. ........................ work by lowering the activation ..................... for the reaction. 3
.......................... are biological catalysts and are made up of proteins. They differ from other
........................... in that they usually work best at 40 C. At higher temperatures they do not work because they are .............................. . Enzymes are used in .............................. detergents and in industries that use fermentation such as brewing and bread-making. They are also used in diagnostic kits for such diseases as ............................... . Here the enzyme helps detect how much .................. is in the blood of the patient. AQA Science © Nelson Thornes Ltd 2006
1 mark each = __/36 marks C2 4
1
C2.4 Rates of reaction
Answers to summary questions 1 The rate of a chemical reaction can be found by measuring how quickly the reactants are used up/consumed or how quickly the products are formed/produced. An example of a chemical reaction is the reaction between calcium carbonate and hydrochloric acid. CaCO3(s) + 2HCl(aq) CaCl2(aq) + H2O(l) + CO2(g) We could measure the rate of this reaction by measuring the mass of the reaction mixture using a top-pan balance. Because carbon dioxide gas is given off, the mass will decrease/go down/be reduced. To see how quickly the reaction is taking place we plot loss in mass (vertical axis) against time (horizontal axis). The steeper the line obtained, the faster/quicker the reaction. We could also measure how quickly the gas is given off by measuring its volume using a gas syringe. In the reaction between sodium thiosulphate and hydrochloric acid, solid sulphur is formed. This makes the reaction mixture cloudy and makes it more difficult to see through the mixture. Eventually we cannot see through the mixture at all and a cross/coin underneath it is obscured/not visible. We can measure the time it takes to do this. 2 There are four main factors that affect the rate of reaction. These are: a) Concentration. This is a measure of how crowded the particles are in a solution and the frequencies of collision. b) Surface area. This is a measure of how much solid is exposed to reaction and therefore how many collisions take place. c) Temperature. This affects the energy of the particles and how quickly they move. It also affects the frequency with which the particles collide and how energetic/efficient the collisions are. The energy required for any reaction to take place is called the activation energy for that reaction. d) The presence of a catalyst. A catalyst will speed up a chemical reaction but is unchanged chemically and weighs the same at the end of the reaction. Catalysts work by lowering the activation energy for the reaction. 3 Enzymes are biological catalysts and are made up of proteins. They differ from other catalysts in that they usually work best at 40 C. At higher temperatures they do not work because they are denatured. Enzymes are used in biological detergents and in industries that use fermentation such as brewing and bread-making. They are also used in diagnostic kits for such diseases as diabetes. Here the enzyme helps detect how much sugar/glucose is in the blood of the patient.
1 mark each = 36 marks
AQA Science © Nelson Thornes Ltd 2006
C2 4
1
C2.5 Energy in reactions .
Name:
Date:
Summary questions Fill in the gaps in the following sentences to test your recall of the facts you have learned in this chapter.
1 a) Exothermic reactions ................................. heat to the surroundings whilst endothermic reactions ................................. heat from the surroundings. b) Respiration is an important ................................. reaction because in the body it is used to produce ................................. energy. ................................. or burning is another example of this type of thermochemical reaction. c) Photosynthesis is an important ............................. reaction because it ............................. light energy to produce sugars and ............................. gas from ............................. dioxide and water. d) The type of reaction (exothermic or endothermic) can be tested by measuring ....................................... changes. e) In reversible reactions if the forward reaction is exothermic then the backward reaction is ............................. . The ...................... amount of energy is released or absorbed in both ....................... . f) In a reversible ...................... we can influence the amounts of products or ...................... by changing the temperature. If the forward reaction is ...................... we can make more of the products by ...................... the temperature. If the forward reaction is ...................... we can make more of the product by lowering the temperature.
[Higher]
2 The equation for the formation of ammonia is given below:
[Higher]
N2(g) + 3H2 ⇌ 2NH3 a) On the left-hand side of the equation there are ...................... gas molecules. b) On the right-hand side of the equation there are ...................... gas molecules. c) If the pressure is raised the system will move to the side which ...................... the pressure. It does this by making ...................... gas molecules. Therefore the equilibrium will move to the ......................-hand side making ...................... ammonia. The actual pressure used is around ...................... atmospheres. d) In the Haber process an ...................... catalyst is used to lower the amount of ...................... needed for the reaction and to ...................... the rate. e) The forward reaction is exothermic and is therefore favoured by a ...................... temperature. This would make the reaction too ...................... and therefore a compromise temperature of ...................... C is used. This makes ...................... ammonia but makes it more quickly.
1 mark each = ___/32 AQA Science © Nelson Thornes Ltd 2006
C2 5
1
C2.5 Energy in reactions
Answers to summary questions 1 a) Exothermic reactions transfer/lose/give out heat to the surroundings whilst endothermic reactions absorb heat from the surroundings. b) Respiration is an important exothermic reaction because in the body it is used to produce heat energy. Combustion or burning is another example of this type of thermochemical reaction. c) Photosynthesis is an important endothermic reaction because it absorbs/uses light energy to produce sugars and oxygen gas from carbon dioxide and water. d) The type of reaction (exothermic or endothermic) can be tested by measuring temperature changes. e) In reversible reactions if the forward reaction is exothermic then the backward reaction is endothermic. The same amount of energy is released or absorbed in both directions. f) In a reversible reaction we can influence the amounts of products or reactants by changing the temperature. If the forward reaction is endothermic we can make more of the products by raising the temperature. If the forward reaction is exothermic we can make more of the product by lowering the temperature. [Higher] 2 The equation for the formation of ammonia is given below:
[Higher]
N2(g) + 3H2 ⇌ 2NH3 a) On the left-hand side of the equation there are 4/more gas molecules. b) On the right-hand side of the equation there are 2/fewer gas molecules. c) If the pressure is raised the system will move to the side which lowers/decreases the pressure. It does this by making fewer gas molecules. Therefore the equilibrium will move to the right-hand side making more ammonia. The actual pressure used is around 250 atmospheres. d) In the Haber process an iron catalyst is used to lower the amount of energy needed for the reaction and to increases the rate. e) The forward reaction is exothermic and is therefore favoured by a lower temperature. This would make the reaction too slow and therefore a compromise temperature of 450 C is used. This makes less ammonia but makes it more quickly.
1 mark each = 32 marks
AQA Science © Nelson Thornes Ltd 2006
C2 5
1
C2.6 Electrolysis Name:
Class:
In each of these sentences select the correct alternatives. 1
a) Electrolysis is the decomposition/synthesis of a substance to give simpler/more complex substances. The substance being electrolysed has to be an ionic/covalent compound. b) The substance being decomposed/synthesised is called the electrolyte/voltameter. c) In electrolysis the electric current enters and leaves the electrolyte/voltameter by insulating/conducting rods called diodes/electrodes. The positive diode/electrode is called the anode/cathode and the negative diode/electrode is called the anode/cathode. d) For electrolysis to occur the electrolyte/voltameter must be in liquid/solid form so that the molecules/ions are free to move. e) In electrolysis the negative ions move towards the anode/cathode. When they get there they gain/lose electrons to form neutral/charged atoms. The positive ions move towards the anode/cathode. When they get there they gain/lose electrons to form neutral/charged atoms.
2
Complete the following electrode half-equations. [Higher] a) 2Br–
Br2 + ..........e–
b) ..........
c) 2O2–
.......... + 4e–
d) Na+ + e–
e) Ca2+ + .......... 3
..........
f)
Cl2 + 2e– ..........
.......... + 2..........
Mg
a) Brine is a solution of .................... .................... in water. The solution contains four ions. These come from the NaCl and the H2O. From NaCl they are .......... and .......... ions. From H2O they are .......... and .......... ions. b) The incomplete symbol equation for the reaction taking place is given below. i)
Complete this equation.
[Higher]
........NaCl(aq) + ........H2O(l)
2NaOH(aq) + Cl2(g) + H2(g)
ii) Write the word equation for the reaction. .......................................................................................................................................... iii) Explain these state symbols: (aq) ...............…..................... 4
(l) ..............…...................
(g) .............…....................
Copper can be purified using electrolysis. a) Name the electrolyte used for this purification. b) What is the substance that is used for i)
the anode? ........................................….... ii) the cathode? ...............................................
1 mark each = ____/47
AQA Science © Nelson Thornes Ltd 2006
C2 6
1
C2.6 Electrolysis
Answers to summary questions 1 a) Electrolysis is the decomposition of a substance to give simpler substances. The substance being electrolysed has to be an ionic compound. b) The substance being decomposed is called the electrolyte. c) In electrolysis the electric current enters and leaves the electrolyte by conducting rods called electrodes. The positive electrode is called the anode and the negative electrode is called the cathode. d) For electrolysis to occur the electrolyte must be in liquid form so that the ions are free to move. e) In electrolysis the negative ions move towards the anode. When they get there they lose electrons to form neutral atoms. The positive ions move towards the cathode. When they get there they gain electrons to form neutral atoms 2)
i) 2Br– Br2 + 2e– – ii) 2Cl Cl2 + 2e– iii) 2O2– O2 + 4e– + – iv) Na + e Na 2+ – v) Ca + 2e Ca vi) Mg2+ + 2e– Mg
3
a)Sodium chloride. Na+ and Cl– H+ and OH–
[Higher]
b) i) 2NaCl(aq) + 2H2O(l) NaOH(aq) + Cl2(g) + H2(g) [Higher] ii) Sodium chloride(aq) + water(l) sodium hydroxide(aq) + chlorine(g) + hydrogen(g) iii) (aq) aqueous or dissolved in water. (l) liquid. (g) gas. 4 a) Copper sulfate solution. b) i) impure copper, ii) pure copper.
1 mark each = 47 marks
AQA Science © Nelson Thornes Ltd 2006
C2 6
1
C2.7 Acids, alkalis and salts Name:
Date:
1 a) All acids ionise in water to give ........+ ions. b) For example, hydrochloric acid, HCl, ionises as follows: HCl
........ + Cl–
c) All alkalis ionise in water to give ........ ions. d) For example, sodium hydroxide, NaOH, ionises as follows: NaOH
........ + OH–
e) The acidity of a solution is measured using the ........ scale. The lower the ........ the ........................ the acid. Neutral ........ has the value of ......... f) ............................ are coloured substances that have different ............................ in the presence of acids and alkalis. Universal indicator is a mixture of ........................ . It is ........................ with strong acid and .......................... with strong alkali. At neutral pH it is .......................... in colour. 2 Salts are substances that contain a metal (or ammonium) part and an acid part. a) Fill in this table. Name of acid
Type of salt formed
Hydrochloric Sulfuric Nitric
b) Salts can be made by reacting acids with reactive metals. The general equation is: acid + metal
salt + hydrogen
Complete this table.
Equation for reaction
Acid
Metal
Hydrochloric
Magnesium
….HCl
+ Sulfuric
Equation for reaction
…………
AQA Science © Nelson Thornes Ltd 2006
Mg
Name of salt
Other product
MgCl2
+
……….
ZnSO4
+
……….
Zinc +
Zn
C2 7
1
C2 7 Summary sheet Continued … c) Salts can be made by reacting acids with insoluble metal oxides or hydroxides called bases. The general equation is: acid + insoluble base
salt + water
Complete this table.
Equation for reaction
Acid
Insoluble base
Nitric
Magnesium oxide
….HNO3
+
Sulfuric Equation for reaction
………….
MgO
Name of salt
Mg(NO3)2
Other product
+ ………….
Copper oxide +
CuO
CuSO4
+
…………
d) When preparing a salt from an insoluble base and acid, the acid is usually ................................ . This speeds up the reaction. The base is added until it stops .................................. . This tells us when the ............................... is finished and all the acid has .............................. . The unreacted base is then ............................ off. The water can be ............................ off by gentle ............................ . The solution is then left for ............................ to form. e) If an acid and an alkali are used to form a salt, there is no way of seeing when the reaction is ...................... . Therefore we use an ........................................ to tell us when this happens. The ............................... changes colour when enough alkali has been added to ................................ the acid.
1 mark each = ____/46
AQA Science © Nelson Thornes Ltd 2006
C2 7
2
C2.7 Acids alkalis and salts
Answers to summary questions H+ HCl H+ + Cl– – OH NaOH Na+ + OH– The acidity of a solution is measured using the pH scale. The lower the pH the stronger the acid. Neutral pH has the value of 7. f) Indicators are coloured substances that have different colours in the presence of acids and alkalis. Universal indicator is a mixture of indicators. It is red with strong acid and purple with strong alkali. At neutral pH it is green in colour. 2 a) 1 a) b) c) d) e)
Name of acid
Type of salt formed
Hydrochloric
chloride
Sulfuric
sulfate
Nitric
nitrate
b)
Equation for reaction
Acid
Metal
Name of salt
Other product
Hydrochloric
Magnesium
Magnesium chloride
Hydrogen
2HCl
+
Sulfuric Equation for reaction
H2SO4
Mg Zinc
+
Zn
MgCl2
+
Zinc sulfate ZnSO4
H2 Hydrogen
+
H2
c)
Equation for reaction
Acid
Insoluble Base
Name of salt
Other product
Nitric
Magnesium oxide
Magnesium nitrate
Water
2HNO3
+
Sulfuric Equation for reaction
H2SO4
MgO Copper oxide
+
CuO
Mg(NO3)2
+
Copper sulfate CuSO4
H2O Water
+
H2O
d) When preparing a salt from an insoluble base and acid, the acid is usually warmed/heated. This speeds up the reaction. The base is added until it stops dissolving. This tells us when the reaction is finished and all the AQA Science © Nelson Thornes Ltd 2006
C2 7
1
C2 7 Summary sheet Continued …
acid has reacted/been used up. The unreacted base is then filtered off. The water can be evaporated off by gentle heating. The solution is then left for crystals to form. e) If an acid and an alkali are used to form a salt, there is no way of seeing when the reaction is complete/finished. Therefore we use an indicator to tell us when this happens. The indicator changes colour when enough alkali has been added to neutralise the acid.
1 mark each = 46 marks
AQA Science © Nelson Thornes Ltd 2006
C2 7
2
C2 End of unit exam questions Name:
Class:
Additional chemistry 1
Match these substances with the descriptions (a) to (e): diamond, hydrogen chloride, magnesium, neon, sodium chloride (a) A compound made of small molecules. .................................................................. (b) A gas at room temperature made of single atoms. ................................................. (c) A giant lattice of atoms that are covalently bonded. ............................................... (d) An ionic solid with a high melting point. .................................................................. (e) A giant lattice that conducts electricity when it is solid. ........................................... (5 marks)
2
(a) Draw a dot and cross diagram to show the electron arrangement of a lithium atom, atomic number 3.
(2 marks) (b) Draw a dot and cross diagram to show the electron arrangement of a fluorine atom, atomic number 9.
(2 marks) (c) Draw dot and cross diagrams to show the ions in lithium fluoride.
(3 marks) 3
Complete the table that shows information about some atoms.
Symbol
Atomic number
Mass number
Number of protons
Number of neutrons
Electron arrangement of atom
Formula of ion
Electron arrangement of ion
Al
13
27
(a)
14
(b)
Al3+
[2,8]3+
O
8
16
8
(c)
2,6
O2–
(d)
K
19
(e)
19
20
2,8,8,1
(f)
[2,8,8]+
Cl
17
35
17
(g)
2,8,7
Cl–
(h) (8 marks)
AQA Science © Nelson Thornes Ltd 2006
C2
1
C2 End of unit exam questions Continued … 4
A student added 20 g of marble chips to 50 cm3 of dilute hydrochloric acid in a conical flask. The flask was put onto a balance. The table shows the mass of gas that was given off. Some marble chips were left in the flask at the end of the reaction. Mass of gas given off (g) Time (minutes)
0
0.14
0.27
0.38
0.47
0.51
0.57
0.59
0.60
0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
(a) Plot a graph of the results. Put time on the horizontal axis and mass lost on the vertical axis. Draw a smooth line through the points, omitting any result that is anomalous.
(5 marks)
(b) The rate of this reaction decreases with time. Explain how you can tell this from the graph. ...............................................................................................................................
(1 mark)
The student decided to extend his work to see if temperature affected the rate at which the gas was produced. (c) (i) Suggest one control variable he should use. .........................................................................................................................
(1 mark)
(ii) Describe how he would control that variable. .........................................................................................................................
(1 mark)
(d) Suggest a suitable range of temperatures he could use. ...............................................................................................................................
(1 mark)
(e) Suggest a suitable interval between temperatures. ...............................................................................................................................
(1 mark)
(f) Use the first set of data to suggest a suitable length of time to leave the reaction. ...............................................................................................................................
AQA Science © Nelson Thornes Ltd 2006
(1 mark)
C2
2
C2 End of unit exam questions Continued … 5
Complete the table that shows information about the electrolysis of different substances. Carbon electrodes were used. Substance
Positive ions present
Negative ions present
Product at negative electrode
Product at positive electrode
Molten magnesium
Mg2+
Cl–
magnesium
(a)
K+
(b)
hydrogen
chlorine
hydrogen
oxygen
(d)
(e)
chloride Aqueous solution of
+
potassium chloride
H
Dilute sulfuric acid
(c)
2–
SO4
–
OH
2–
Aqueous solution of
Cu2+
SO4
copper(II) sulfate
H+
OH– (5 marks)
6
Ammonium sulfate (NH4)2SO4, is an important fertiliser. It is made by reacting ammonia solution with sulfuric acid. The reaction can be represented by the equation: H2SO4(aq) + 2NH4OH(aq)
(NH4)2SO4(aq) + 2H2O(l)
(a) How can you tell from the equation that ammonium sulfate is soluble? ...............................................................................................................................
(1 mark)
(b) (i) Which ions make the sulfuric acid solution acidic? .........................................................................................................................
(1 mark)
(ii) Which ions make the ammonia solution alkaline? .........................................................................................................................
(1 mark)
(iii) What name is used to describe the reaction between these ions? .........................................................................................................................
(1 mark)
(c) A student made 15.4 g of ammonium sulfate from 0.2 moles of sulfuric acid. (i) What is the mass of one mole of ammonium sulfate? ......................................................................................................................... .........................................................................................................................
AQA Science © Nelson Thornes Ltd 2006
(2 marks)
C2
3
C2 End of unit exam questions Continued … (ii) What mass of ammonium sulfate can be made from 0.2 moles of sulfuric acid, according to the equation? .........................................................................................................................
(1 mark)
(iii) What was the percentage yield of ammonium sulfate obtained by the student? ......................................................................................................................... .........................................................................................................................
(2 marks) [Higher]
Total = ___/44 marks
AQA Science © Nelson Thornes Ltd 2006
C2
4
C2 End of unit exam question answers
Additional chemistry 1
(a) hydrogen chloride (b) neon (c) diamond (d) sodium chloride (e) magnesium
2
(1 mark each, total 5 marks)
(a) Li or dot at centre of two concentric circles, inner circle with two dots/crosses, outer circle with one dot/cross. (all correct = 2 marks, one error or omission = 1 mark) (b) For dot at centre of two concentric circles, inner circle with two dots/crosses, outer circle with seven dots/crosses. (all correct = 2 marks, one error or omission = 1 mark) (c) Lithium ion: EITHER Li+ or [Li]+ OR Li at centre of circle with two dots/crosses (with brackets) and + at top right-hand side. (1 mark) Fluoride ion: EITHER F at centre of two concentric circles with two dots/crosses on inner circle and eight dots/crosses on outer circle (surrounded by brackets) with – at top right-hand side OR F surrounded by eight dots/crosses with – at top right-hand side. (2 marks) (It is acceptable to show only the outer electrons in bonding diagrams)
3
(a) 13 (b) 2,8,3 (c) 8 (d) [2,8]2– (allow 2,8) (e) 39 (f) K+ (g) 18 (h) [2,8,8]– (allow 2,8,8)
4
(1 mark each, total 8 marks)
(a) One mark each for: • Both axes labelled. • Suitable scales used. • All points correctly plotted (+/– half small square). • Smooth line through points. • Omitting point at 5 minutes.
(5 marks)
(b) Slope/gradient decreases with time OR slope/gradient/line is steeper at the beginning or becomes less steep or levels off. (1 mark) (c) (i) E.g. concentration of acid; size of marble chips. (1 mark) (ii) Linked to the above e.g. ensure that the same concentration of acid is used for each temperature. (1 mark) (d) E.g. 20°C to 60°C – reasonable within practical and safety limits.(1 mark) (e) At least five, equally spaced.
(1 mark)
(f) About four minutes.
(1 mark)
AQA Science © Nelson Thornes Ltd 2006
C2
1
C2 End of unit exam question answers Continued … (a) chlorine
5
(1 mark)
(b) Cl– and OH– (accept with correct state symbols, i.e. aq) +
6
+
+
+
(1 mark)
(c) H (accept H3O , H (aq), H3O (aq))
(1 mark)
(d) copper
(1 mark)
(e) oxygen
(1 mark)
(a) Its state symbol is (aq)/it is aqueous. +
+
+
(1 mark) +
(b) (i) Hydrogen ions/H /H (aq)/H3O /H3O (aq). (ii) Hydroxide ions/OH–/OH–(aq). (iii) Neutralisation.
(1 mark) (1 mark) (1 mark)
(c) (i)
132 g (2 marks for correct answer with units) (correct working, e.g. (14 + 4) 2 + 32 + (16 4) gains 1 mark) (ii) 26.4 g (1 mark) (iii) 58.3% (2 marks for correct answer) (correct working, e.g. 15.4 100/26.4 (e.c.f. from (ii) can gain 2 marks)
Total = 44 marks
AQA Science © Nelson Thornes Ltd 2006
C2
2
Score Date C2.1 Structures and Bonding
___ / 33
C2.2 Structures and Properties C2.3 How much?
___ / 37 ___/ 39
C2.4 Rates of Reaction
___ / 36
C2.5 Energy and Reactions
___ / 32
C2.6 Electrolysis
___/ 47
C2.7 Acids, Alkalis and Salts
___/ 46
End of unit exam
___/ 46
S Williams Nov ‘10
Grade %
90+ 80
A* A
70 60 50 40 30 20
B C D E F G
C2.1 Structures and bonding Name:
Date:
Summary questions Fill in the gaps in the following sentences to test your recall of the facts you have learned in this chapter. 1
a) The centre of an atom is called the ........................................... . b) In the centre of the atom there are two types of sub-atomic particles. These particles are the ........................ and the ........................... . The ............................ are positively charged. The ........................ have no charge. They are neutral. c) The centre of the atom is .................................. charged. This is because of the positively charged sub-atomic particles called ..................... . d) Around the centre are negatively charged sub-atomic particles called .................... . e) The overall charge on an atom is zero. Therefore the number of .............................. and .......................... are equal. f)
The electrons are arranged in energy ........................ around the centre of the atom.
g) The first energy ...................... is nearest to the centre and can take a maximum of ................ electrons. h) The second and third energy .......................... can take a maximum of .................... electrons each. i)
The first .................... level is filled with electrons first and then the ...................... and third ones.
j)
When atoms bond with other atoms, the number of .................... in their outermost energy .................... changes.
2
a) In ionic bonding, electrons from one atom are .............................. to another. b) The charged particles formed are called .................. . c) Negative ions are formed when atoms .................... electrons. d) Positive ions are formed when atoms .................... electrons. e) An example of an ionic compound is ........................ chloride. f)
............................ bonds are formed when pairs of electrons are .................... between atoms.
g) An example of a .............................. substance is water. h) Diamond is an example of a ..................... covalent substance. i)
Dots and .................... represent the electrons in these two types of bonding.
j)
In metals the positively charged metal .............. are arranged in ........................ .
k) The .......................... of metal ions are in a ................ of free .............................. .
Total = ___/33 AQA Science © Nelson Thornes Ltd 2006
C2 1
1
Student Answer Booklet CHEMISTRY C2.1 Structures and Bonding Answers to summary questions 1 a) The centre of an atom is called the nucleus. b) In the centre of the atom there are two types of sub-atomic particles. These particles are the proton and the neutron. The protons are positively charged. The neutrons have no charge. They are neutral. c) The centre of the atom is positively charged. This is because of the positively charged sub-atomic particles called protons. d) Around the centre are negatively charged sub-atomic particles called electrons. e) The overall charge on an atom is zero. Therefore the number of electrons and protons are equal. f) The electrons are arranged in energy levels around the centre of the atom. g) The first energy level is nearest to the centre and can take a maximum of two electrons. h) The second and third energy levels can take a maximum of eight electrons each. i) The first level is filled with electrons first and then the second and third ones. j) When atoms bond with other atoms, the number of electrons in their outermost energy level changes. 2 a) In ionic bonding, electrons from one atom are transferred/given to another. b) The charged particles formed are called ions. c) Negative ions are formed when atoms gain electrons. d) Positive ions are formed when atoms lose electrons. e) An example of an ionic compound is sodium/calcium/magnesium/potassium etc. chloride. f) Covalent bonds are formed when pairs of electrons are shared between atoms. g) An example of a covalent substance is water. h) Diamond is an example of a giant covalent substance. i) Dots and crosses represent the electrons in these two types of bonding. j) In metals the positively charged metal ions/cations are arranged in layers. k) The layers of metal ions are in a sea of free electrons.
1 mark for each word in bold Total = 33 marks
AQA Science © Nelson Thornes Ltd 2006
C2 1
1
C2.2 Structures and properties Name:
Date:
Summary questions Answer the following questions to test your recall and understanding of what you have learned in this chapter. 1
2
Decide which of these statements are true and which are false. a) Ionic compounds have high melting points.
True/false
b) This is because the bonds between the molecules present are strong.
True/false
c) Ionic compounds conduct electricity in the solid state.
True/false
d) In solid ionic compounds the ions can move and carry the current.
True/false
e) Covalently bonded compounds tend to have low melting and boiling points.
True/false
f)
True/false
Intermolecular forces are strong and make it difficult to separate the molecules.
g) Diamond and graphite are also simple covalent molecules.
True/false
h) Covalent substances do not conduct electricity.
True/false
i)
Graphite conducts electricity.
True/false
j)
Graphite is slippery because the bonds between the atoms are weak covalent bonds. True/false
In this question, cross out the wrong alternatives. Ionic compounds have low/high melting points because the forces of attraction between the ions/molecules are strong. When they are in solid/liquid form, ionic compounds are poor electrical conductors because the ions/electrons are free/unable to move and carry the electrical current. Covalent substances tend to be good/poor electrical conductors because the ions/electrons are free/unable to move. Graphite/diamond is an exception because it has ions/electrons which are free/unable to move and carry the electrical current. Graphite/diamond is the hardest natural substance known because all its bonds are strong/weak covalent bonds. Graphite/diamond is a very slippery substance because the bonds between/inside the layers of carbon atoms are weak/strong and easily broken so the layers can slide over each other easily. Metals are good/poor electrical conductors because the ions/electrons are free/unable to move and carry the electrical current. These free electrons/ions are able to move in both the liquid and solid forms. The free electrons/ions hold the metal lattice together. Metals are malleable/brittle because the layers can/cannot slide over each other. This is because as the distortion to the metal lattice occurs, the electrons/ions can also move and hold the metal molecules/ions together. Nanoparticles are very small/large particles that have properties different from/the same as the substances when they are in bulk form.
AQA Science © Nelson Thornes Ltd 2006
1 mark each = ___/37 C2 2
1
C2 2 Exam-style questions Continued …
AQA Science © Nelson Thornes Ltd 2006
C2 2
2
C2.2 Structures and Properties
Answers to summary questions 1 a) True. Ionic bonds are strong. b) False. Ionic compounds are not made up of molecules they are made up of ions. c) False. They conduct electricity in the liquid state but not the solid state. d) False. They are in fixed positions and cannot move. e) True. Covalently bonded compounds tend to have low melting and boiling points. f) False. The intermolecular forces are weak and this is why the boiling points are low. g) False. They are giant covalent molecular substances. h) True. They have no free electrons or ions (apart from graphite). i) True. It has free electrons. j) False. It is slippery but the reason given is wrong. The layers of atoms are held together by weak intermolecular forces called van der Waals forces. 2 The correct answers are in bold. Ionic compounds have high melting points because the forces of attraction between the ions are strong. When they are in solid form, ionic compounds are poor electrical conductors because the ions are unable to move and carry the electrical current. Covalent substances tend to be poor electrical conductors because the electrons are unable to move. Graphite is an exception because it has electrons which are free to move and carry the electrical current. Diamond is the hardest natural substance known because all its bonds are strong covalent bonds. Graphite is a very slippery substance because the bonds between the layers of carbon atoms are weak and easily broken so the layers can slide over each other easily. Metals are good electrical conductors because the electrons are free to move and carry the electrical current. These free electrons are able to move in both the liquid and solid forms. The free electrons hold the metal lattice together. Metals are malleable because the layers can slide over each other. This is because as the distortion to the metal lattice occurs, the electrons can also move and hold the metal ions together. Nanoparticles are very small particles that have properties different from the substances when they are in bulk form.
1 mark each = 37 marks
AQA Science © Nelson Thornes Ltd 2006
C2 2
1
C2.3 How much? Summary sheet Name:
Class:
Summary questions Answer the following questions to test your recall and understanding of what you have learned in this chapter. 1
a) What is the name given to atoms of the same element which have different mass numbers? .................................................................................................................................................. b) These atoms have different numbers of which sub-atomic particle? .................................................................................................................................................. c) In the periodic table which two properties of an element are usually given as numbers? .................................................................................................................................................. d) How is the formula mass of a compound calculated? .................................................................................................................................................. .................................................................................................................................................. .................................................................................................................................................. e) The relative atomic mass of carbon-12 expressed in grams is called a ………………… of carbon atoms. f)
In the reaction below, 1 mol of oxygen molecules reacts with how many moles of magnesium atoms? 2Mg + O2 2MgO ..................................................................................................................................................
g) What is the relative formula mass of MgO?
[relative atomic masses: Mg = 24; O = 16]
.................................................................................................................................................. .................................................................................................................................................. h) If 92 g of sodium react with 32 g of oxygen. What is the empirical formula of the compound formed?
[relative atomic masses: Na = 23; O = 16] [Higher]
.................................................................................................................................................. .................................................................................................................................................. ..................................................................................................................................................
AQA Science © Nelson Thornes Ltd 2006
C2 3
1
C2 3 Summary sheet Continued … 2
a) Balance the following equations. i)
[Higher]
….Mg + ….CO2 ….MgO + ….C
ii) ….Fe
+ ….Cl2 ……FeCl3
iii) ….N2
+ ….H2
….NH3
iv) ….Al
+ ….O2
……Al2O3
v) ….NH3 + ….CuO ….Cu + ….N2 + …..H2O b) In the reaction below what mass of fluorine will react exactly with 120 g of magnesium? Mg + F2 MgF2
[relative atomic masses Mg = 24; F = 19] [Higher]
.................................................................................................................................................. .................................................................................................................................................. .................................................................................................................................................. .................................................................................................................................................. c) When the experiment in b) was done what mass of magnesium fluoride would you expect to be formed?
[Higher]
.................................................................................................................................................. d) What is the percentage yield if 248 g of magnesium fluoride was actually formed?
[Higher]
.................................................................................................................................................. .................................................................................................................................................. e) What is a reversible reaction? .................................................................................................................................................. f)
What symbol represents a reversible reaction? .........................................................................
g) What can you say about the forward and backward reaction if a reversible reaction when equilibrium is reached? .................................................................................................................................................. 3
a) What industrial process is used to make ammonia? .................................................................................................................................................. b) What are the conditions for making ammonia? .................................................................................................................................................. c) Give a major use of ammonia. .................................................................................................................................................. d) Give one major environmental drawback of this use. ..................................................................................................................................................
AQA Science © Nelson Thornes Ltd 2006
Total = ___/39
C2 3
2
C2.3 How much? Summary sheet Teacher notes
Answers to summary questions Answers 1 a) b) c) d) e) f) g) h)
Isotopes. (1 mark) Neutrons. (1 mark) Atomic or proton number and relative atomic mass or mass number. (2 marks) By adding up the relative atomic masses of the atoms present. (1 mark) Mole. (1 mark) 2 mol of magnesium atoms react with one mole of oxygen molecules. (1 mark) 24 + 16 = 40 (1 mark) Sodium Oxygen [Higher] 92 g 32 g 92 32 mol mol (1 mark) 23 16 4 mol of sodium combine with 2 mol of oxygen. (1 mark) 2 mol of sodium combine with 1 mol of oxygen. (1 mark) formula is Na2O (3 marks total)
2 a) i) 2Mg + CO2 2MgO + C [Higher] ii) 2Fe + 3Cl2 2FeCl3 [Higher] iii) N2 + 3H2 2NH3 [Higher] iv) 4Al + 3O2 2Al2O3 [Higher] or 2Al + 1½O2 Al2O3 [Higher] v) 2NH3 + 3CuO 3Cu + N2 + 3H2O [Higher] b) There are two ways of answering this. [Higher] i) 120 g =
(2 marks) (2 marks) (2 marks) (2 marks) (2 marks) (2 marks)
120 mol of Mg 24
From the equation, 1 mol of Mg reacts with 1 mol of F2 5 mol of Mg react with 5 mol of F2 5 mol of F2 = 5 (2 19) = 190 g ii) From the equation, 24 g of Mg react with 38 g of F2 38 1 g of Mg reacts with g of F2 24 38 120 g of magnesium react with 120 g of F2 = 190 g 24 c) 190 + 120 = 310 g 248 d) Yield = 100% = 80% [Higher] 310 e) A reaction that can go both ways/backwards and forwards. f) ⇌ g) They have the same rate. 3 a) b) c) d)
(2 marks) (2 marks) (2 marks) (2 marks) (1 mark) (1 mark)
Haber. (1 mark) 250 atmospheres, 450 C and an iron catalyst. (3 marks) Fertilisers. (1 mark) Eutrophication – they cause algal blooms when they leech into rivers and lakes. (1 mark)
AQA Science © Nelson Thornes Ltd 2006
Total = 39 marks
C2 3
1
C2.4 Rates of reaction Summary sheet Name:
Class:
Summary questions Fill in the gaps in the following paragraphs to test your understanding of this chapter. 1
The rate of a chemical reaction can be found by measuring how ........................ the reactants are ............................ or how quickly the products are ....................... . An example of a chemical reaction is the reaction between calcium carbonate and hydrochloric acid: CaCO3(s) + 2HCl(aq) CaCl2(aq) + H2O(l) + CO2(g) We could measure the rate of this reaction by measuring the ..................... of the reaction mixture using a top-pan balance. Because .............................. ........................... gas is given off, the mass will ............................... . To see how quickly the reaction is taking place we plot .............. in mass (vertical axis) against ................. (horizontal axis). The steeper the line obtained, the .................... the reaction. We could also measure how quickly the gas is given off by measuring its volume using a gas ..................... . In the reaction between sodium thiosulphate and hydrochloric acid, solid sulphur is formed. This makes the reaction mixture ........................... and makes it more difficult to see ....................... the mixture. Eventually we cannot see .......................... the mixture at all and a ................................... underneath it is .......................... . We can measure the .................... it takes to do this.
2
There are four main factors that affect the rate of reaction. These are: a) ......................... . This is a measure of how crowded the particles are in a solution and the frequencies of ........................ . b) ........................ ......................... . This is a measure of how much solid is exposed to reaction and therefore how many ............................... take place. c) ......................... . This affects the energy of the particles and how quickly they ...................... . It also affects the ................... with which the particles collide and how .............................. the collisions are. The energy required for any reaction to take place is called the ......................... energy for that reaction. d) The presence of a ............................ . A ...................... will speed up a chemical reaction but is ............................. chemically and weighs the same at the end of the reaction. ........................ work by lowering the activation ..................... for the reaction. 3
.......................... are biological catalysts and are made up of proteins. They differ from other
........................... in that they usually work best at 40 C. At higher temperatures they do not work because they are .............................. . Enzymes are used in .............................. detergents and in industries that use fermentation such as brewing and bread-making. They are also used in diagnostic kits for such diseases as ............................... . Here the enzyme helps detect how much .................. is in the blood of the patient. AQA Science © Nelson Thornes Ltd 2006
1 mark each = __/36 marks C2 4
1
C2.4 Rates of reaction
Answers to summary questions 1 The rate of a chemical reaction can be found by measuring how quickly the reactants are used up/consumed or how quickly the products are formed/produced. An example of a chemical reaction is the reaction between calcium carbonate and hydrochloric acid. CaCO3(s) + 2HCl(aq) CaCl2(aq) + H2O(l) + CO2(g) We could measure the rate of this reaction by measuring the mass of the reaction mixture using a top-pan balance. Because carbon dioxide gas is given off, the mass will decrease/go down/be reduced. To see how quickly the reaction is taking place we plot loss in mass (vertical axis) against time (horizontal axis). The steeper the line obtained, the faster/quicker the reaction. We could also measure how quickly the gas is given off by measuring its volume using a gas syringe. In the reaction between sodium thiosulphate and hydrochloric acid, solid sulphur is formed. This makes the reaction mixture cloudy and makes it more difficult to see through the mixture. Eventually we cannot see through the mixture at all and a cross/coin underneath it is obscured/not visible. We can measure the time it takes to do this. 2 There are four main factors that affect the rate of reaction. These are: a) Concentration. This is a measure of how crowded the particles are in a solution and the frequencies of collision. b) Surface area. This is a measure of how much solid is exposed to reaction and therefore how many collisions take place. c) Temperature. This affects the energy of the particles and how quickly they move. It also affects the frequency with which the particles collide and how energetic/efficient the collisions are. The energy required for any reaction to take place is called the activation energy for that reaction. d) The presence of a catalyst. A catalyst will speed up a chemical reaction but is unchanged chemically and weighs the same at the end of the reaction. Catalysts work by lowering the activation energy for the reaction. 3 Enzymes are biological catalysts and are made up of proteins. They differ from other catalysts in that they usually work best at 40 C. At higher temperatures they do not work because they are denatured. Enzymes are used in biological detergents and in industries that use fermentation such as brewing and bread-making. They are also used in diagnostic kits for such diseases as diabetes. Here the enzyme helps detect how much sugar/glucose is in the blood of the patient.
1 mark each = 36 marks
AQA Science © Nelson Thornes Ltd 2006
C2 4
1
C2.5 Energy in reactions .
Name:
Date:
Summary questions Fill in the gaps in the following sentences to test your recall of the facts you have learned in this chapter.
1 a) Exothermic reactions ................................. heat to the surroundings whilst endothermic reactions ................................. heat from the surroundings. b) Respiration is an important ................................. reaction because in the body it is used to produce ................................. energy. ................................. or burning is another example of this type of thermochemical reaction. c) Photosynthesis is an important ............................. reaction because it ............................. light energy to produce sugars and ............................. gas from ............................. dioxide and water. d) The type of reaction (exothermic or endothermic) can be tested by measuring ....................................... changes. e) In reversible reactions if the forward reaction is exothermic then the backward reaction is ............................. . The ...................... amount of energy is released or absorbed in both ....................... . f) In a reversible ...................... we can influence the amounts of products or ...................... by changing the temperature. If the forward reaction is ...................... we can make more of the products by ...................... the temperature. If the forward reaction is ...................... we can make more of the product by lowering the temperature.
[Higher]
2 The equation for the formation of ammonia is given below:
[Higher]
N2(g) + 3H2 ⇌ 2NH3 a) On the left-hand side of the equation there are ...................... gas molecules. b) On the right-hand side of the equation there are ...................... gas molecules. c) If the pressure is raised the system will move to the side which ...................... the pressure. It does this by making ...................... gas molecules. Therefore the equilibrium will move to the ......................-hand side making ...................... ammonia. The actual pressure used is around ...................... atmospheres. d) In the Haber process an ...................... catalyst is used to lower the amount of ...................... needed for the reaction and to ...................... the rate. e) The forward reaction is exothermic and is therefore favoured by a ...................... temperature. This would make the reaction too ...................... and therefore a compromise temperature of ...................... C is used. This makes ...................... ammonia but makes it more quickly.
1 mark each = ___/32 AQA Science © Nelson Thornes Ltd 2006
C2 5
1
C2.5 Energy in reactions
Answers to summary questions 1 a) Exothermic reactions transfer/lose/give out heat to the surroundings whilst endothermic reactions absorb heat from the surroundings. b) Respiration is an important exothermic reaction because in the body it is used to produce heat energy. Combustion or burning is another example of this type of thermochemical reaction. c) Photosynthesis is an important endothermic reaction because it absorbs/uses light energy to produce sugars and oxygen gas from carbon dioxide and water. d) The type of reaction (exothermic or endothermic) can be tested by measuring temperature changes. e) In reversible reactions if the forward reaction is exothermic then the backward reaction is endothermic. The same amount of energy is released or absorbed in both directions. f) In a reversible reaction we can influence the amounts of products or reactants by changing the temperature. If the forward reaction is endothermic we can make more of the products by raising the temperature. If the forward reaction is exothermic we can make more of the product by lowering the temperature. [Higher] 2 The equation for the formation of ammonia is given below:
[Higher]
N2(g) + 3H2 ⇌ 2NH3 a) On the left-hand side of the equation there are 4/more gas molecules. b) On the right-hand side of the equation there are 2/fewer gas molecules. c) If the pressure is raised the system will move to the side which lowers/decreases the pressure. It does this by making fewer gas molecules. Therefore the equilibrium will move to the right-hand side making more ammonia. The actual pressure used is around 250 atmospheres. d) In the Haber process an iron catalyst is used to lower the amount of energy needed for the reaction and to increases the rate. e) The forward reaction is exothermic and is therefore favoured by a lower temperature. This would make the reaction too slow and therefore a compromise temperature of 450 C is used. This makes less ammonia but makes it more quickly.
1 mark each = 32 marks
AQA Science © Nelson Thornes Ltd 2006
C2 5
1
C2.6 Electrolysis Name:
Class:
In each of these sentences select the correct alternatives. 1
a) Electrolysis is the decomposition/synthesis of a substance to give simpler/more complex substances. The substance being electrolysed has to be an ionic/covalent compound. b) The substance being decomposed/synthesised is called the electrolyte/voltameter. c) In electrolysis the electric current enters and leaves the electrolyte/voltameter by insulating/conducting rods called diodes/electrodes. The positive diode/electrode is called the anode/cathode and the negative diode/electrode is called the anode/cathode. d) For electrolysis to occur the electrolyte/voltameter must be in liquid/solid form so that the molecules/ions are free to move. e) In electrolysis the negative ions move towards the anode/cathode. When they get there they gain/lose electrons to form neutral/charged atoms. The positive ions move towards the anode/cathode. When they get there they gain/lose electrons to form neutral/charged atoms.
2
Complete the following electrode half-equations. [Higher] a) 2Br–
Br2 + ..........e–
b) ..........
c) 2O2–
.......... + 4e–
d) Na+ + e–
e) Ca2+ + .......... 3
..........
f)
Cl2 + 2e– ..........
.......... + 2..........
Mg
a) Brine is a solution of .................... .................... in water. The solution contains four ions. These come from the NaCl and the H2O. From NaCl they are .......... and .......... ions. From H2O they are .......... and .......... ions. b) The incomplete symbol equation for the reaction taking place is given below. i)
Complete this equation.
[Higher]
........NaCl(aq) + ........H2O(l)
2NaOH(aq) + Cl2(g) + H2(g)
ii) Write the word equation for the reaction. .......................................................................................................................................... iii) Explain these state symbols: (aq) ...............…..................... 4
(l) ..............…...................
(g) .............…....................
Copper can be purified using electrolysis. a) Name the electrolyte used for this purification. b) What is the substance that is used for i)
the anode? ........................................….... ii) the cathode? ...............................................
1 mark each = ____/47
AQA Science © Nelson Thornes Ltd 2006
C2 6
1
C2.6 Electrolysis
Answers to summary questions 1 a) Electrolysis is the decomposition of a substance to give simpler substances. The substance being electrolysed has to be an ionic compound. b) The substance being decomposed is called the electrolyte. c) In electrolysis the electric current enters and leaves the electrolyte by conducting rods called electrodes. The positive electrode is called the anode and the negative electrode is called the cathode. d) For electrolysis to occur the electrolyte must be in liquid form so that the ions are free to move. e) In electrolysis the negative ions move towards the anode. When they get there they lose electrons to form neutral atoms. The positive ions move towards the cathode. When they get there they gain electrons to form neutral atoms 2)
i) 2Br– Br2 + 2e– – ii) 2Cl Cl2 + 2e– iii) 2O2– O2 + 4e– + – iv) Na + e Na 2+ – v) Ca + 2e Ca vi) Mg2+ + 2e– Mg
3
a)Sodium chloride. Na+ and Cl– H+ and OH–
[Higher]
b) i) 2NaCl(aq) + 2H2O(l) NaOH(aq) + Cl2(g) + H2(g) [Higher] ii) Sodium chloride(aq) + water(l) sodium hydroxide(aq) + chlorine(g) + hydrogen(g) iii) (aq) aqueous or dissolved in water. (l) liquid. (g) gas. 4 a) Copper sulfate solution. b) i) impure copper, ii) pure copper.
1 mark each = 47 marks
AQA Science © Nelson Thornes Ltd 2006
C2 6
1
C2.7 Acids, alkalis and salts Name:
Date:
1 a) All acids ionise in water to give ........+ ions. b) For example, hydrochloric acid, HCl, ionises as follows: HCl
........ + Cl–
c) All alkalis ionise in water to give ........ ions. d) For example, sodium hydroxide, NaOH, ionises as follows: NaOH
........ + OH–
e) The acidity of a solution is measured using the ........ scale. The lower the ........ the ........................ the acid. Neutral ........ has the value of ......... f) ............................ are coloured substances that have different ............................ in the presence of acids and alkalis. Universal indicator is a mixture of ........................ . It is ........................ with strong acid and .......................... with strong alkali. At neutral pH it is .......................... in colour. 2 Salts are substances that contain a metal (or ammonium) part and an acid part. a) Fill in this table. Name of acid
Type of salt formed
Hydrochloric Sulfuric Nitric
b) Salts can be made by reacting acids with reactive metals. The general equation is: acid + metal
salt + hydrogen
Complete this table.
Equation for reaction
Acid
Metal
Hydrochloric
Magnesium
….HCl
+ Sulfuric
Equation for reaction
…………
AQA Science © Nelson Thornes Ltd 2006
Mg
Name of salt
Other product
MgCl2
+
……….
ZnSO4
+
……….
Zinc +
Zn
C2 7
1
C2 7 Summary sheet Continued … c) Salts can be made by reacting acids with insoluble metal oxides or hydroxides called bases. The general equation is: acid + insoluble base
salt + water
Complete this table.
Equation for reaction
Acid
Insoluble base
Nitric
Magnesium oxide
….HNO3
+
Sulfuric Equation for reaction
………….
MgO
Name of salt
Mg(NO3)2
Other product
+ ………….
Copper oxide +
CuO
CuSO4
+
…………
d) When preparing a salt from an insoluble base and acid, the acid is usually ................................ . This speeds up the reaction. The base is added until it stops .................................. . This tells us when the ............................... is finished and all the acid has .............................. . The unreacted base is then ............................ off. The water can be ............................ off by gentle ............................ . The solution is then left for ............................ to form. e) If an acid and an alkali are used to form a salt, there is no way of seeing when the reaction is ...................... . Therefore we use an ........................................ to tell us when this happens. The ............................... changes colour when enough alkali has been added to ................................ the acid.
1 mark each = ____/46
AQA Science © Nelson Thornes Ltd 2006
C2 7
2
C2.7 Acids alkalis and salts
Answers to summary questions H+ HCl H+ + Cl– – OH NaOH Na+ + OH– The acidity of a solution is measured using the pH scale. The lower the pH the stronger the acid. Neutral pH has the value of 7. f) Indicators are coloured substances that have different colours in the presence of acids and alkalis. Universal indicator is a mixture of indicators. It is red with strong acid and purple with strong alkali. At neutral pH it is green in colour. 2 a) 1 a) b) c) d) e)
Name of acid
Type of salt formed
Hydrochloric
chloride
Sulfuric
sulfate
Nitric
nitrate
b)
Equation for reaction
Acid
Metal
Name of salt
Other product
Hydrochloric
Magnesium
Magnesium chloride
Hydrogen
2HCl
+
Sulfuric Equation for reaction
H2SO4
Mg Zinc
+
Zn
MgCl2
+
Zinc sulfate ZnSO4
H2 Hydrogen
+
H2
c)
Equation for reaction
Acid
Insoluble Base
Name of salt
Other product
Nitric
Magnesium oxide
Magnesium nitrate
Water
2HNO3
+
Sulfuric Equation for reaction
H2SO4
MgO Copper oxide
+
CuO
Mg(NO3)2
+
Copper sulfate CuSO4
H2O Water
+
H2O
d) When preparing a salt from an insoluble base and acid, the acid is usually warmed/heated. This speeds up the reaction. The base is added until it stops dissolving. This tells us when the reaction is finished and all the AQA Science © Nelson Thornes Ltd 2006
C2 7
1
C2 7 Summary sheet Continued …
acid has reacted/been used up. The unreacted base is then filtered off. The water can be evaporated off by gentle heating. The solution is then left for crystals to form. e) If an acid and an alkali are used to form a salt, there is no way of seeing when the reaction is complete/finished. Therefore we use an indicator to tell us when this happens. The indicator changes colour when enough alkali has been added to neutralise the acid.
1 mark each = 46 marks
AQA Science © Nelson Thornes Ltd 2006
C2 7
2
C2 End of unit exam questions Name:
Class:
Additional chemistry 1
Match these substances with the descriptions (a) to (e): diamond, hydrogen chloride, magnesium, neon, sodium chloride (a) A compound made of small molecules. .................................................................. (b) A gas at room temperature made of single atoms. ................................................. (c) A giant lattice of atoms that are covalently bonded. ............................................... (d) An ionic solid with a high melting point. .................................................................. (e) A giant lattice that conducts electricity when it is solid. ........................................... (5 marks)
2
(a) Draw a dot and cross diagram to show the electron arrangement of a lithium atom, atomic number 3.
(2 marks) (b) Draw a dot and cross diagram to show the electron arrangement of a fluorine atom, atomic number 9.
(2 marks) (c) Draw dot and cross diagrams to show the ions in lithium fluoride.
(3 marks) 3
Complete the table that shows information about some atoms.
Symbol
Atomic number
Mass number
Number of protons
Number of neutrons
Electron arrangement of atom
Formula of ion
Electron arrangement of ion
Al
13
27
(a)
14
(b)
Al3+
[2,8]3+
O
8
16
8
(c)
2,6
O2–
(d)
K
19
(e)
19
20
2,8,8,1
(f)
[2,8,8]+
Cl
17
35
17
(g)
2,8,7
Cl–
(h) (8 marks)
AQA Science © Nelson Thornes Ltd 2006
C2
1
C2 End of unit exam questions Continued … 4
A student added 20 g of marble chips to 50 cm3 of dilute hydrochloric acid in a conical flask. The flask was put onto a balance. The table shows the mass of gas that was given off. Some marble chips were left in the flask at the end of the reaction. Mass of gas given off (g) Time (minutes)
0
0.14
0.27
0.38
0.47
0.51
0.57
0.59
0.60
0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
(a) Plot a graph of the results. Put time on the horizontal axis and mass lost on the vertical axis. Draw a smooth line through the points, omitting any result that is anomalous.
(5 marks)
(b) The rate of this reaction decreases with time. Explain how you can tell this from the graph. ...............................................................................................................................
(1 mark)
The student decided to extend his work to see if temperature affected the rate at which the gas was produced. (c) (i) Suggest one control variable he should use. .........................................................................................................................
(1 mark)
(ii) Describe how he would control that variable. .........................................................................................................................
(1 mark)
(d) Suggest a suitable range of temperatures he could use. ...............................................................................................................................
(1 mark)
(e) Suggest a suitable interval between temperatures. ...............................................................................................................................
(1 mark)
(f) Use the first set of data to suggest a suitable length of time to leave the reaction. ...............................................................................................................................
AQA Science © Nelson Thornes Ltd 2006
(1 mark)
C2
2
C2 End of unit exam questions Continued … 5
Complete the table that shows information about the electrolysis of different substances. Carbon electrodes were used. Substance
Positive ions present
Negative ions present
Product at negative electrode
Product at positive electrode
Molten magnesium
Mg2+
Cl–
magnesium
(a)
K+
(b)
hydrogen
chlorine
hydrogen
oxygen
(d)
(e)
chloride Aqueous solution of
+
potassium chloride
H
Dilute sulfuric acid
(c)
2–
SO4
–
OH
2–
Aqueous solution of
Cu2+
SO4
copper(II) sulfate
H+
OH– (5 marks)
6
Ammonium sulfate (NH4)2SO4, is an important fertiliser. It is made by reacting ammonia solution with sulfuric acid. The reaction can be represented by the equation: H2SO4(aq) + 2NH4OH(aq)
(NH4)2SO4(aq) + 2H2O(l)
(a) How can you tell from the equation that ammonium sulfate is soluble? ...............................................................................................................................
(1 mark)
(b) (i) Which ions make the sulfuric acid solution acidic? .........................................................................................................................
(1 mark)
(ii) Which ions make the ammonia solution alkaline? .........................................................................................................................
(1 mark)
(iii) What name is used to describe the reaction between these ions? .........................................................................................................................
(1 mark)
(c) A student made 15.4 g of ammonium sulfate from 0.2 moles of sulfuric acid. (i) What is the mass of one mole of ammonium sulfate? ......................................................................................................................... .........................................................................................................................
AQA Science © Nelson Thornes Ltd 2006
(2 marks)
C2
3
C2 End of unit exam questions Continued … (ii) What mass of ammonium sulfate can be made from 0.2 moles of sulfuric acid, according to the equation? .........................................................................................................................
(1 mark)
(iii) What was the percentage yield of ammonium sulfate obtained by the student? ......................................................................................................................... .........................................................................................................................
(2 marks) [Higher]
Total = ___/44 marks
AQA Science © Nelson Thornes Ltd 2006
C2
4
C2 End of unit exam question answers
Additional chemistry 1
(a) hydrogen chloride (b) neon (c) diamond (d) sodium chloride (e) magnesium
2
(1 mark each, total 5 marks)
(a) Li or dot at centre of two concentric circles, inner circle with two dots/crosses, outer circle with one dot/cross. (all correct = 2 marks, one error or omission = 1 mark) (b) For dot at centre of two concentric circles, inner circle with two dots/crosses, outer circle with seven dots/crosses. (all correct = 2 marks, one error or omission = 1 mark) (c) Lithium ion: EITHER Li+ or [Li]+ OR Li at centre of circle with two dots/crosses (with brackets) and + at top right-hand side. (1 mark) Fluoride ion: EITHER F at centre of two concentric circles with two dots/crosses on inner circle and eight dots/crosses on outer circle (surrounded by brackets) with – at top right-hand side OR F surrounded by eight dots/crosses with – at top right-hand side. (2 marks) (It is acceptable to show only the outer electrons in bonding diagrams)
3
(a) 13 (b) 2,8,3 (c) 8 (d) [2,8]2– (allow 2,8) (e) 39 (f) K+ (g) 18 (h) [2,8,8]– (allow 2,8,8)
4
(1 mark each, total 8 marks)
(a) One mark each for: • Both axes labelled. • Suitable scales used. • All points correctly plotted (+/– half small square). • Smooth line through points. • Omitting point at 5 minutes.
(5 marks)
(b) Slope/gradient decreases with time OR slope/gradient/line is steeper at the beginning or becomes less steep or levels off. (1 mark) (c) (i) E.g. concentration of acid; size of marble chips. (1 mark) (ii) Linked to the above e.g. ensure that the same concentration of acid is used for each temperature. (1 mark) (d) E.g. 20°C to 60°C – reasonable within practical and safety limits.(1 mark) (e) At least five, equally spaced.
(1 mark)
(f) About four minutes.
(1 mark)
AQA Science © Nelson Thornes Ltd 2006
C2
1
C2 End of unit exam question answers Continued … (a) chlorine
5
(1 mark)
(b) Cl– and OH– (accept with correct state symbols, i.e. aq) +
6
+
+
+
(1 mark)
(c) H (accept H3O , H (aq), H3O (aq))
(1 mark)
(d) copper
(1 mark)
(e) oxygen
(1 mark)
(a) Its state symbol is (aq)/it is aqueous. +
+
+
(1 mark) +
(b) (i) Hydrogen ions/H /H (aq)/H3O /H3O (aq). (ii) Hydroxide ions/OH–/OH–(aq). (iii) Neutralisation.
(1 mark) (1 mark) (1 mark)
(c) (i)
132 g (2 marks for correct answer with units) (correct working, e.g. (14 + 4) 2 + 32 + (16 4) gains 1 mark) (ii) 26.4 g (1 mark) (iii) 58.3% (2 marks for correct answer) (correct working, e.g. 15.4 100/26.4 (e.c.f. from (ii) can gain 2 marks)
Total = 44 marks
AQA Science © Nelson Thornes Ltd 2006
C2
2
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