ElectrochemistryCambridge IGCSE Chemistry: Topic test

20 questions, 54 marks

Cambridge IGCSE Chemistry

Electrochemistry topic test

Total 54 marks

Name

Class

Date

1
A technician melts pure solid lead(II) iodide, PbI2, in a crucible and passes an electric current through it using two inert graphite electrodes dipped into the molten compound.
(a)
What is formed at the cathode (negative electrode) during this electrolysis?
[1 mark]
AIodine
BLead
COxygen
DHydrogen
(b)
What is formed at the anode (positive electrode) during this electrolysis?
[1 mark]
AIodine
BLead
CHydrogen
DWater
(c)
Write the half-equation for the reaction that occurs at the cathode during this electrolysis.
[2 marks]
Total for question 1: 4 marks
2
A metal refining company purifies impure copper using electrolysis. An impure block of copper is used as the anode and a thin sheet of pure copper is used as the cathode, both dipped into a solution of aqueous copper(II) sulfate.
(a)
What happens at the anode during this electrolysis?
[1 mark]
ACopper atoms lose electrons and dissolve into solution as copper ions
BCopper ions gain electrons and are deposited as copper metal
COxygen gas is released
DSulfate ions are deposited as solid sulfur
(b)
What happens at the cathode during this electrolysis?
[1 mark]
ACopper atoms lose electrons and dissolve into solution
BCopper ions from the solution gain electrons and are deposited as pure copper metal
CHydrogen gas is released
DThe cathode dissolves away
(c)
Explain why the mass of the impure copper anode decreases while the mass of the pure copper cathode increases during this process.
[2 marks]
Total for question 2: 4 marks
3
A swimming pool disinfectant company produces chlorine gas by electrolysing concentrated aqueous sodium chloride solution (brine) using inert electrodes.
(a)
State the products formed at the anode and at the cathode during this electrolysis, and name the third substance remaining in solution.
[3 marks]
(b)
Explain, in terms of ion discharge, why chlorine gas is formed at the anode rather than oxygen, even though the solution contains hydroxide ions as well as chloride ions, given that the solution is concentrated.
[4 marks]
Total for question 3: 7 marks
4
A technician melts pure solid zinc chloride, ZnCl2, and passes an electric current through it using two inert graphite electrodes.
(a)
Describe, with reference to the movement of electrons and ions, how charge is transferred through the whole circuit during this electrolysis, from the power supply, through the electrodes, to the molten zinc chloride and back.
[6 marks]
(b)
Write balanced ionic half-equations for the reactions at the cathode and at the anode, and use them to construct the overall balanced symbol equation for the electrolysis of molten zinc chloride.
[6 marks]
Total for question 4: 12 marks
5
A logistics warehouse replaces its fleet of lead-acid battery-powered forklift trucks with forklifts powered by hydrogen-oxygen fuel cells.
(a)
What is the only chemical product formed when a hydrogen-oxygen fuel cell produces electricity?
[1 mark]
ACarbon dioxide
BNitrogen oxides
CWater
DHydrogen peroxide
(b)
Which of the following is an advantage of using hydrogen-oxygen fuel cells rather than petrol or diesel engines to power the forklifts?
[1 mark]
AFuel cells release large amounts of carbon dioxide when operating
BHydrogen fuel is easier to store safely than petrol
CFuel cells require no maintenance at all
DFuel cells produce no carbon dioxide at the point of use, only water
(c)
State one disadvantage of using hydrogen-oxygen fuel cells to power the warehouse forklifts compared with using petrol or diesel engines.
[2 marks]
Total for question 5: 4 marks
6
A student carries out two separate electrolysis experiments using aqueous copper(II) sulfate solution as the electrolyte. In experiment 1, two inert graphite electrodes are used. In experiment 2, two copper electrodes are used instead.
(a)
What is formed at the anode in experiment 1, using inert graphite electrodes?
[1 mark]
AHydrogen gas
BCopper metal
COxygen gas
DSulfur dioxide gas
(b)
Which statement correctly describes what happens at the anode in experiment 2, using copper electrodes, instead of what happens with inert electrodes?
[1 mark]
AOxygen gas is still released, exactly as with inert electrodes
BThe copper anode remains completely unchanged
CHydrogen gas is released instead of oxygen
DThe copper anode itself dissolves, releasing copper ions into the solution, instead of a gas being released
(c)
State what is formed at the cathode in both experiment 1 and experiment 2, and explain why the cathode product is the same in both cases.
[2 marks]
Total for question 6: 4 marks
7
A jeweller wants to electroplate a cheap metal bracelet with a thin, even layer of pure silver to improve its appearance and resistance to corrosion. The bracelet is connected as the cathode in an electrolytic cell containing a solution of a soluble silver salt, with a bar of pure silver used as the anode.
(a)
Describe what happens at the cathode (the bracelet) and at the anode (the pure silver bar) during this electroplating process.
[3 marks]
(b)
Explain two reasons why the jeweller chooses to electroplate the bracelet with silver rather than leaving it as the cheaper base metal.
[4 marks]
Total for question 7: 7 marks
8
A hospital is deciding whether to replace its diesel-powered backup generators with hydrogen-oxygen fuel cells to provide emergency electricity during power cuts.
(a)
Explain, in terms of the chemical reaction taking place, why a hydrogen-oxygen fuel cell is able to generate electricity, and state the only chemical product formed.
[6 marks]
(b)
Evaluate whether the hospital should replace its diesel generators with hydrogen-oxygen fuel cells, discussing at least one advantage and one disadvantage of making this change.
[6 marks]
Total for question 8: 12 marks

End of questions