A student carries out displacement reactions by adding small pieces of four metals (magnesium, zinc, iron and copper) to separate test tubes of dilute hydrochloric acid. She records how vigorously each metal reacts.
(a)State the general trend in reactivity of the four metals shown by this test.(1)
(b)Use the reactivity series to put these four metals in order, from most reactive to least reactive.(2)
(Total for Question 1 is 3 marks)
2
Iron is extracted from iron oxide by heating with carbon in a blast furnace. Aluminium is extracted from aluminium oxide by electrolysis.
(a)Name the type of chemical reaction that occurs when iron oxide reacts with carbon to form iron.(1)
(b)Explain why aluminium cannot be extracted from its oxide by heating with carbon, but iron can.(3)
(c)Give one reason, other than reactivity, why extracting aluminium is more expensive than extracting iron.(1)
(Total for Question 2 is 5 marks)
3
When magnesium ribbon is added to copper sulfate solution, a displacement reaction occurs. The blue colour of the solution fades and a reddish-brown solid forms.
(a)Write the balanced symbol equation for this reaction, including state symbols.(3)
(b)In terms of electrons, explain why magnesium is oxidised in this reaction.(2)
(c)Write the half equation for the reduction reaction taking place.(2)
(Total for Question 3 is 7 marks)
4
A student reacts 3.0 g of magnesium ribbon with excess dilute hydrochloric acid. Mg + 2HCl -> MgCl2 + H2. Relative atomic masses: H = 1, Mg = 24, Cl = 35.5. The molar volume of a gas at room temperature and pressure is 24 dm3 (24000 cm3).
(a)Calculate the number of moles of magnesium in 3.0 g.(2)
(b)Calculate the mass of magnesium chloride, MgCl2, produced.(3)
(c)Calculate the volume, in dm3, of hydrogen gas produced at room temperature and pressure.(2)
(d)Describe a test to confirm the gas produced is hydrogen, including the result.(2)
(Total for Question 4 is 9 marks)
5
Sulfuric acid reacts with different bases.
(a)Complete the word equation: copper oxide + sulfuric acid -> ___ + ___(2)
(b)Write the balanced symbol equation for the reaction between sodium hydroxide and sulfuric acid, given the products are sodium sulfate and water.(3)
(c)Write the ionic equation for neutralisation that applies to any strong acid reacting with any alkali.(2)
(Total for Question 5 is 7 marks)
6
Universal indicator can be used to estimate the pH of a solution.
(a)State the pH value of a neutral solution.(1)
(b)A solution turns universal indicator red. State whether this solution is a strong acid, weak acid, strong alkali or weak alkali, and give its approximate pH.(2)
(Total for Question 6 is 3 marks)
7
Hydrochloric acid is a strong acid. Ethanoic acid is a weak acid. Both solutions have the same concentration, 0.1 mol/dm3.
(a)Explain the difference between a strong acid and a weak acid in terms of ionisation.(2)
(b)State and explain which of the two solutions would have the lower pH.(3)
(c)A solution of hydrochloric acid has a pH of 2. Predict the pH of a solution of hydrochloric acid that has a hydrogen ion concentration 10 times greater.(1)
(Total for Question 7 is 6 marks)
8
Required practical: A student is asked to prepare a pure, dry sample of copper sulfate crystals from copper oxide (an insoluble base) and dilute sulfuric acid. Outline of method: warm some dilute sulfuric acid; add copper oxide powder to the acid a little at a time, stirring, until the copper oxide is in excess (some solid remains undissolved); filter the mixture; gently heat the filtrate to evaporate some of the water until the point of crystallisation; leave to cool and crystallise; filter off the crystals and pat dry with filter paper.
(a)Explain why the copper oxide is added until it is in excess.(2)
(b)Name the piece of apparatus used to separate the excess copper oxide from the copper sulfate solution, and name the process.(2)
(c)Explain why the solution is heated only until the point of crystallisation is reached, rather than heating until it is completely dry.(2)
(d)The student reacted 4.0 g of copper oxide with excess sulfuric acid, then obtained 8.5 g of hydrated copper sulfate crystals, CuSO4.5H2O. Relative atomic masses: Cu = 64, O = 16, S = 32, H = 1. Calculate the percentage yield of crystals.(4)
(e)Suggest one reason why the percentage yield is less than 100%.(1)
(Total for Question 8 is 11 marks)
9
In a titration, 25.0 cm3 of sodium hydroxide solution of unknown concentration was exactly neutralised by 15.0 cm3 of 0.100 mol/dm3 hydrochloric acid. NaOH + HCl -> NaCl + H2O
(a)Calculate the number of moles of hydrochloric acid used.(2)
(b)Calculate the concentration, in mol/dm3, of the sodium hydroxide solution.(3)
(c)State the colour change of the indicator that would be seen at the end point if phenolphthalein was used, starting with excess sodium hydroxide.(1)
(Total for Question 9 is 6 marks)
10
Lead bromide, PbBr2, is a solid at room temperature but conducts electricity and can be electrolysed when molten.
(a)Explain why solid lead bromide does not conduct electricity, but molten lead bromide does.(2)
(b)Name the product formed at the cathode (negative electrode) during electrolysis of molten lead bromide, and explain why it forms there.(2)
(c)Write the half equation for the reaction at the anode.(2)
(Total for Question 10 is 6 marks)
11
Required practical: A student investigates the electrolysis of copper sulfate solution using inert (graphite) electrodes.
(a)Name the product observed forming at the cathode, and describe what is seen.(2)
(b)Explain, in terms of ions present, why oxygen gas (rather than sulfate) is produced at the anode.(3)
(c)Write the half equation for the reaction occurring at the cathode.(2)
(d)A different student repeats the experiment using copper electrodes instead of inert electrodes, and finds the blue colour of the solution does not change. Explain this observation, and state a use of this process.(3)
(Total for Question 11 is 10 marks)
12
Iron is extracted from iron oxide (haematite) by reduction with carbon in a blast furnace. Aluminium is extracted from aluminium oxide (dissolved in molten cryolite) by electrolysis. Compare the two extraction methods, including reference to reactivity, the chemical processes involved, and the relative cost/energy requirements of each method.
(Total for Question 12 is 6 marks)
13
Answer the following multiple choice questions about chemical changes.
(a)Which gas is tested for using a lit splint that produces a squeaky pop?(1)
A) Oxygen
B) Hydrogen
C) Carbon dioxide
D) Chlorine
(b)Which piece of equipment is used to accurately measure the volume of acid added during a titration?(1)
A) Measuring cylinder
B) Beaker
C) Burette
D) Conical flask
(c)Which ion is always produced when an acid dissolves in water?(1)
A) OH-
B) H+
C) Na+
D) Cl-
(d)Which of these correctly describes reduction?(1)
A) Gain of oxygen
B) Loss of oxygen
C) Loss of hydrogen
D) Gain of protons
(Total for Question 13 is 4 marks)
14
A student adds dilute hydrochloric acid to calcium carbonate chips in a flask, and bubbles of gas are produced.
(a)Write the word equation for this reaction.(2)
(b)Describe a test for the gas produced, including the positive result.(2)
(c)The student repeats the experiment using calcium carbonate powder instead of chips, with the same mass and same concentration of acid. Explain the effect this has on the rate of reaction.(2)
(Total for Question 14 is 6 marks)
15
0.24 g of magnesium ribbon is reacted with excess dilute sulfuric acid. Mg + H2SO4 -> MgSO4 + H2. Relative atomic mass of Mg = 24. The molar volume of a gas at room temperature and pressure is 24000 cm3/mol.
(a)Show that the volume of hydrogen gas produced is 240 cm3.(3)
(Total for Question 15 is 3 marks)
16
Dilute sulfuric acid is corrosive.
(a)Give one piece of safety equipment that should be worn when handling dilute sulfuric acid.(1)
(b)State one hazard symbol that would appear on a bottle of concentrated sulfuric acid, and what it means.(2)
(Total for Question 16 is 3 marks)
17
A student adds sodium hydroxide solution, a little at a time, to 25 cm3 of hydrochloric acid and measures the pH after each addition using a pH probe. The table shows her results. Volume of NaOH added (cm3): 0, 5, 10, 15, 20, 25 pH: 1, 2, 3, 7, 11, 12
(a)Identify the volume of sodium hydroxide needed to exactly neutralise the acid.(1)
(b)Describe the shape of the graph of pH (y-axis) against volume of NaOH added (x-axis) that these results would produce.(2)
(Total for Question 17 is 3 marks)
18
A group of students electrolyse different aqueous solutions using inert electrodes and record the gas produced at each electrode.
(a)Predict the gas produced at the anode when concentrated sodium chloride solution is electrolysed, and explain your answer.(2)
(b)Predict the gas produced at the cathode when dilute sulfuric acid is electrolysed, and explain your answer.(2)
(Total for Question 18 is 4 marks)
19
Iron is extracted from iron(III) oxide, Fe2O3, in the blast furnace: 2Fe2O3 + 3C -> 4Fe + 3CO2. Relative atomic masses: Fe = 56, O = 16, C = 12.
(a)Calculate the relative formula mass of Fe2O3.(1)
(b)Calculate the atom economy of this reaction for the production of iron, giving your answer to 1 decimal place.(4)
(Total for Question 19 is 5 marks)
20
A student adds four metals (A, B, C and D) to solutions of salts of the other metals and records whether a displacement reaction occurs. Metal A added to a solution of a salt of B: reaction occurs Metal B added to a solution of a salt of C: reaction occurs Metal B added to a solution of a salt of D: reaction occurs Metal D added to a solution of a salt of C: reaction occurs Metal C added to a solution of a salt of A: no reaction
(a)Use the results to deduce the order of reactivity of metals A, B, C and D, from most to least reactive.(3)
(b)Explain, in terms of particles, why metal A is able to displace metal B from a solution of B's salt.(2)
(Total for Question 20 is 5 marks)
Mark scheme · C4 Chemical Changes
Question 1
(a) B1 the more reactive the metal, the more vigorous/faster the reaction with the acid (oe)
(a) Answer: More reactive metals react more vigorously and quickly with the acid.
(b) B1 at least three metals placed in the correct relative order
(b) B1 fully correct order: magnesium, zinc, iron, copper cao
(b) Answer: Magnesium > zinc > iron > copper
Question 2
(a) B1 reduction (oe)
(a) Answer: Reduction
(b) B1 aluminium is more reactive than carbon, but iron is less reactive than carbon
(b) B1 carbon can only reduce (displace) metals that are less reactive than carbon itself
(b) B1 so carbon can reduce iron oxide but cannot reduce (remove oxygen from) aluminium oxide
(b) Answer: Aluminium is more reactive than carbon so carbon cannot displace it; iron is less reactive than carbon so carbon can reduce iron oxide.
(c) B1 e.g. electrolysis requires large amounts of electrical energy, which is expensive; or the aluminium oxide must be melted, which needs a lot of energy (oe, any sensible cost-related reason)
(c) Answer: Electrolysis uses large amounts of electrical energy, which is costly.
Question 3
(a) M1 correct formulae: Mg, CuSO4, MgSO4, Cu
(a) M1 equation correctly balanced (1:1:1:1)
(a) A1 all four state symbols correct: (s), (aq), (aq), (s) cao
(b) M1 at the same concentration, hydrochloric acid produces a higher concentration of H+ ions
(b) M1 because it is a strong acid and ionises fully, whereas ethanoic acid only partially ionises, so produces fewer H+ ions (oe)
(b) Answer: Hydrochloric acid has the lower pH because it fully ionises, giving a higher H+ ion concentration.
(c) B1 pH 1 cao
(c) Answer: pH 1
Question 8
(a) M1 to ensure that all of the sulfuric acid has reacted / to use up all of the acid
(a) M1 so that the excess (unreacted) solid copper oxide can be removed by filtration, leaving a salt solution with no excess acid
(a) Answer: So that all the acid reacts and the excess solid copper oxide can then be filtered off.
(b) B1 filter paper and funnel
(b) B1 filtration
(b) Answer: Filter paper and funnel; the process is filtration.
(c) M1 heating to complete dryness could decompose the crystals or drive off the water of crystallisation too quickly, forming a powder
(c) M1 cooling slowly from the crystallisation point allows larger, well-formed pure crystals to grow (oe)
(c) Answer: To avoid decomposing/over-drying the salt and to allow large, well-formed crystals to grow on slow cooling.
(d) M1 moles of CuO = 4.0 / 80 = 0.05 (mol)
(d) M1 Mr of CuSO4.5H2O = 250 correctly calculated
(d) M1 theoretical yield = 0.05 x 250 = 12.5 (g)
(d) A1 percentage yield = 8.5 / 12.5 x 100 = 68% cao
(d) Answer: 68%
(e) B1 e.g. some product/solution was lost during filtration or transfer between containers; some crystals were lost when drying; the reaction did not go to completion (any sensible practical loss reason)
(e) Answer: Some solution or crystals were lost during filtration, transfer or drying.
Question 9
(a) M1 correct substitution: 0.100 x 15.0 / 1000
(a) A1 1.5 x 10-3 mol (0.0015 mol) cao
(a) Answer: 1.5 x 10-3 mol
(b) M1 moles of NaOH = moles of HCl = 1.5 x 10-3 (mol) (ft from part a, 1:1 ratio)
(b) M1 concentration = moles / volume in dm3 = 1.5 x 10-3 / 0.0250
(b) A1 0.06 mol/dm3 cao
(b) Answer: 0.06 mol/dm3
(c) B1 pink to colourless
(c) Answer: Pink to colourless
Question 10
(a) M1 in the solid, the ions are held in a fixed lattice/position and cannot move
(a) M1 when molten, the ions are free to move and can carry charge/current
(a) Answer: Solid ions are fixed in place; molten ions are free to move and carry charge.
(b) M1 lead (metal) forms at the cathode
(b) M1 positive Pb2+ ions are attracted to the negative electrode (cathode) (oe)
(b) Answer: Lead forms at the cathode because Pb2+ ions are attracted to the negative electrode.
(c) M1 correct species shown: 2Br- and Br2
(c) A1 2Br- -> Br2 + 2e- correctly balanced cao
(c) Answer: 2Br- -> Br2 + 2e-
Question 11
(a) B1 copper (metal)
(a) B1 a pink/orange-brown coating (deposit) forms on the electrode
(a) Answer: Copper metal is deposited, seen as a pink/orange-brown coating on the electrode.
(b) M1 the ions present in solution include Cu2+, SO4 2-, H+ and OH- (from water)
(b) M1 sulfate ions are not discharged at the anode
(b) M1 OH- ions (from water) are discharged in preference, producing oxygen gas and water (oe)
(b) Answer: Sulfate ions are not discharged; hydroxide ions from water are discharged instead, producing oxygen.
(c) M1 correct species shown: Cu2+ and Cu with 2e-
(c) A1 Cu2+ + 2e- -> Cu correctly balanced cao
(c) Answer: Cu2+ + 2e- -> Cu
(d) M1 at the anode, copper atoms dissolve into solution as Cu2+ ions
(d) M1 at the cathode, copper is deposited from Cu2+ ions in solution at approximately the same rate, so the concentration of Cu2+ ions (and blue colour) stays constant
(d) M1 this process is used to purify copper (oe)
(d) Answer: Copper anode dissolves as fast as copper is deposited at the cathode, keeping Cu2+ concentration constant; used to purify copper.
Question 12
Level 1 (1-2): Simple, isolated statements about one method, or basic facts about reactivity, with little or no linkage between ideas.
Level 2 (3-4): A description of both extraction methods with some reference to reactivity and either the chemical process or the relative cost/energy, showing some linking of ideas.
Level 3 (5-6): A detailed and coherent comparison of both methods, including the reactivity position relative to carbon, the type of chemical reaction occurring in each case, and a clear explanation of the relative energy/cost differences, with a logical structure throughout.
Indicative content:
Iron is less reactive than carbon, so it can be extracted by reduction with carbon (iron oxide + carbon -> iron + carbon dioxide).
Aluminium is more reactive than carbon, so carbon cannot reduce aluminium oxide; aluminium must be extracted by electrolysis instead.
In the blast furnace, carbon (via carbon monoxide) removes oxygen from iron oxide (reduction).
In electrolysis, molten aluminium oxide is split into aluminium and oxygen using electrical energy; Al3+ ions gain electrons at the cathode (reduction).
Electrolysis requires large amounts of electrical energy to melt the aluminium oxide (very high melting point, hence cryolite is used to lower it) and to drive the reaction, making it much more expensive/energy-intensive than reduction with carbon.
Extraction of iron by carbon reduction is cheaper and requires less energy than extraction of aluminium by electrolysis.
Question 13
(a) B1 B cao
(a) Answer: B) Hydrogen
(b) B1 C cao
(b) Answer: C) Burette
(c) B1 B cao
(c) Answer: B) H+
(d) B1 B cao
(d) Answer: B) Loss of oxygen
Question 14
(a) B1 calcium chloride and water named as products