GCSE Questions and Answers Redox Chemistry and Electrolysis

1

GCSE Questions and Answers

Redox Chemistry and Electrolysis.

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6 consecutive CCEA GCSE Chemistry papers: 2002-7

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3 Electrolysis plays an important part in extracting some metals from their ores and in purifying others.

a) Define what is meant by the term electrolysis.

_______________________________________________________________ [2]

b) Name one metal which is obtained from its ore by electrolysis.

______________________________ [1]

2002, Paper 1

3 Electrolysis plays an important part in extracting some metals from their ores and in purifying

others.

a) Define what is meant by the term electrolysis.Electrolysis is decomposition [1] of a substance using an electric current [1]

b) Name one metal which is obtained from its ore by electrolysis.Any reactive metal at the top of the reactivity series. Specification refers to aluminium [1]; but could accept sodium, potassium, calcium, magnesium, zinc.

c) Draw a labelled diagram of simple laboratory apparatus which shows how copper can be purified.

c) Draw a labelled diagram of simple laboratory apparatus which

shows how copper can be purified.

Complete circuit (1)

(1)(1)

Electrolyte (1)

(1)

(1)

Accept any soluble copper salt

d) Write balanced, ionic equations to show the electrode reactions which occur when copper is purified.

(i) At the anode ________________ [2]

(ii) At the cathode ______________ [2]

d) Write balanced, ionic equations to show the electrode reactions which occur when copper is purified.

(i) At the anode Cu → Cu2+ + 2e- [2]

(ii) At the cathode Cu2+ + 2e- → Cu [2]

e) Which particles are responsible for the conductivity of electricity in:

(i) metals? ____________________ [1]

(ii) electrolytes? ________________ [1]

e) Which particles are responsible for the conductivity of electricity in:

(i) metals? Electrons [1]

(ii) electrolytes? Ions [1]

f) Give two uses of copper metal apart from its use in electrical wiring.________________________________________________________ [2]

f) Give two uses of copper metal apart from its use in electrical wiring.

Specification lists:PlumbingBrass Any two for [1] eachCoinage

[2]

g) The electrolysis of dilute sulphuric acid using inert electrodes produces two gases as products.

(i) Name a material which could be used as the electrodes in this experiment.___________________________ [1]

(ii) Name the product formed at the anode _______________cathode _____________ [2]

g) The electrolysis of dilute sulphuric acid using inert electrodes produces two gases as products.

(i) Name a material which could be used as the electrodes in this experiment.Graphite (or platinum) [1]

(ii) Name the product formed at the anode oxygen [1] accept O2

cathode hydrogen [1] accept H2

(iii) Write balanced, ionic equations to show how these gases are formed.

Anode reaction ______________[2]

Cathode reaction _____________[2]

(iii) Write balanced, ionic equations to show how these gases are formed.

Anode reaction2H2O → O2 + 4H+ + 4e-

or 4OH- → 2H2O + O2 + 4e-

or 4OH- → 4e- + 2H2O + H2 [2]

Cathode reaction2H+ + 2e- → H2 [2]

4 a) What term is used to describe a reaction which gives out heat?

__________________________ [1]

2002,Paper 1

4 a) What term is used to describe a reaction which gives out heat?

Exothermic [1]

b) When drops of water are added to anhydrous copper sulphate heat is given out.

(i) Describe what would be observed during this reaction._______________________________________________________________ [2]

(ii) The addition of water to anhydrous copper sulphate is called

______________________________ [1]

b) When drops of water are added to anhydrous copper sulphate heat is given out.

(i) Describe what would be observed during this reaction.The white [1] solid would turn blue [1]

(ii) The addition of water to anhydrous copper sulphate is called

Hydration [1]

c) Heat is also given out during the reaction of sodium hydroxide with hydrochloric

acid.

(i) Give a balanced symbol equation for this reaction.______________________________ [2]

(ii) The reaction of an acid with an alkali is

called ________________________ [1]

c) Heat is also given out during the reaction of sodium hydroxide with hydrochloric

acid.

(i) Give a balanced symbol equation for this reaction.NaOH + HCl → NaCl + H2O [2]

(ii) The reaction of an acid with an alkali is

called Neutralisation [1]

d) The redox reaction of zinc with copper sulphate solution also gives out heat.

(i) Describe what would be observed during this reaction._______________________________________________________________ [2]

(ii) Give a balanced symbol equation for this equation. _____________________ [2]

d) The redox reaction of zinc with copper sulphate solution also gives out heat.

(i) Describe what would be observed during this reaction.

The silvery/grey[1] zinc would become coated with red/brown[1] copper metal. The blue [1] solution fades / colourless /

zinc disappears / bubbles[1] / green[1]. Max [2](ii) Give a balanced symbol equation for this equation.

Zn + CuSO4 → ZnSO4 + Cuor Zn + Cu2+ → Zn2+ + Cu [2]

(iii) The reaction of zinc with copper sulphate solution is an example of

______________________________ [1]

(iv) Explain this redox reaction in terms of electron transfer. _________________________________

________________________________________________________________________________________________ [5]

(iii) The reaction of zinc with copper sulphate solution is an example of

Displacement [1]

(iv) Explain this redox reaction in terms of electron transfer. The zinc has lost electrons [1] and is

therefore oxidised [1]. The copper ions have gained electrons [1] and are therefore reduced [1]. Redox is reduction and oxidation taking place together [1]

1 Aluminium is the most abundant metallic element in the Earth’s crust, making up approximately 8% of the crust. The ore is first purified and the metal is then extracted from the purified ore by electrolysis.

2003, Paper 2

a) Explain what you understand by the term “electrolysis”._________________________________________________________ [2]

b) Name the ore from which aluminium is extracted.___________________________ [1]

a) Explain what you understand by the term “electrolysis”.Electrolysis is the breaking down / decomposing / splitting of a substance by passing electricity through it. [2]

b) Name the ore from which aluminium is extracted.Bauxite – accept alumina [1]

c) The electrolysis of the purified ore is carried out in the Hall-Héroult cell. In this cell the anode and cathode are made of graphite. The electrolyte is molten aluminium oxide dissolved in cryolite, Na3AlF6.

(i) Explain what is meant by each of the terms below:Anode _____________________ [1]Cathode ___________________ [1]Electrolyte _________________ [2]

(i) Explain what is meant by each of the terms below:Anode is the positive electrode [1]Cathode is the negative electrode [1]Electrolyte is the substance through which the electricity passes [1] and is broken down [1]

(ii) Give two reasons why graphite is a suitable material from which to make the anode and cathode.

_______________________________________________________ [2]

(iii) Why is the aluminium oxide dissolved in molten cryolite?

__________________________ [2]

(ii) Give two reasons why graphite is a suitable material from which to make the anode and cathode.

Graphite is a good conductor [1] and is cheaper (than platinum)/inert [1]

(iii) Why is the aluminium oxide dissolved in molten cryolite?The molten cryolite lowers the melting point of the aluminium oxide / so reducing costs / saving energy [1] increase conductivity [1]

d)(i)Name the products formed a the electrodes during electrolysis and give balanced, ionic equations for the reactions taking place.

Anode Cathode

Name of Product

Balanced ionic equation

d)(i)Name the products formed a the electrodes during electrolysis and give balanced, ionic equations for the reactions taking place.

Anode CathodeName of Product

Oxygen [1] Aluminium [1]

Balanced ionic equation

2O2- → O2 + 4e- [1]6O2- → 3O2 + 12e- [2]

Al3+ 3e- → Al [2]Or 4Al3+ + 12e- → 4Al [2]

(ii) At which electrode is reduction taking place? Explain your answer.

____________________________________________________________________________________ [3]

(ii) At which electrode is reduction taking place? Explain your answer.

Reduction is taking place at the cathode [1]. Reduction is the gain of the electrons [1] the aluminium ions are gaining electrons [1]

e) Aluminium is an extremely important metal with widespread uses. Give two uses of aluminium and the property on which each use depends.

Use ______________________ [1]Property __________________ [2]Use ______________________ [1]Property __________________ [2]

e) Aluminium is an extremely important metal with widespread uses. Give two uses of aluminium and the property on which each use depends.

Use overhead power cables [1]Property low density / good conductor [1]Use Alloy [1]Property low density (but high strength) [1]

Use saucepans [1]Property good thermal conductor [1]

f) Aluminium is widely recycled. Suggest two reasons why aluminium metal is recycled.

_______________________________________________________ [2]

f) Aluminium is widely recycled. Suggest two reasons why aluminium metal is recycled.

Aluminium is expensive to extract from its ore/cheaper to recycle [1] Bauxite reserves are running out/reduces landfill [1]

6a) The diagram below shows the apparatus used to carry out the electrolysis of molten lithium bromide using graphite electrodes.

2004, Paper 2

(i) What is meant by the term electrolysis? _______________________________ _______________________________ [2]

(ii) During the electrolysis of molten lithium bromide, what would be observed at the

anode? _______________________________ _______________________________ [2]

(i) What is meant by the term electrolysis?Decomposition/breakdown [1] of compounds using (a direct current of) electricity [1] [2]

(ii) During the electrolysis of molten lithium bromide, what would be observed at the

anode?Anode = brown [1] pungent [1] gas [1] evolved. Any two [2]

(iii) Write a balanced ionic equation for the reaction occurring at the anode.

_______________________________ [3]

(iv) Explain as fully as possible why the bulb does not light when the lithium bromide is solid. _______________________________ _______________________________ _______________________________ [3]

(iii) Write a balanced ionic equation for the reaction occurring at the anode.

Anode = 2Br- → Br2 + 2e- [3]

(iv) Explain as fully as possible why the bulb does not light when the lithium bromide is solid.Ions [1] cannot move [1] when solid so no flow of current / conduction / circuit incomplete [1] [3]

b) The diagram below shows the apparatus used to carry out the electrolysis of dilute sulphuric acid using platinum electrodes. Hydrogen gas and oxygen gas are evolved.

(i) Give two reasons why platinum is used for the electrodes. _______________________________ _______________________________ [2]

(ii) Write a balanced ionic equation for the reaction occurring at the anode.

_______________________________ [3]

(i) Give two reasons why platinum is used for the electrodes.Conducts electricity [1] inert/does not react with acid [2]

(ii) Write a balanced ionic equation for the reaction occurring at the anode.

Anode = 4OH- → O2 + 2H2O + 4e- [3]

(iii) Describe the test you could use to confirm the presence of:Oxygen Gas ________________________ _______________________________ [2]

Hydrogen Gas ______________________ _______________________________ [2]

(iii) Describe the test you could use to confirm the presence of:

Oxygen Gas glowing splint [1] relights [1]

Hydrogen Gas lit splint [1] pops/explosion [1]

4a) Aluminium is a reactive metal which is difficult to extract from its ore. Before 1886 it was made by heating aluminium chloride with sodium.

Aluminium chloride + sodium → aluminium + sodium chloride

2005, Paper 2

(i) Write a balanced symbol equation for this reaction._______________________________ [2]

(ii) Suggest a metal which could be used instead of sodium._______________________________ [1]

(i) Write a balanced symbol equation for this reaction.

AlCl3 + 3Na → Al + 3NaCl [2]

(ii) Suggest a metal which could be used instead of sodium.

K/Mg/Ca [1]

b) Today, aluminium is produced industrially by electrolysis of dissolved pure

aluminium oxide, as shown in the diagram below. Pure aluminium oxide has a melting point of 2050°C.

(i) Name parts A, B and C and substances D and E.A __________________________B __________________________C __________________________D __________________________E __________________________ [5]

(i) Name parts A, B and C and substances D and E.

A anode/positive electrode [1] B steel cell/tank [1] C cathode/negative electrode [1] D aluminium [1]E cryolite [1]

(ii) What is the formula for aluminium oxide?_______________________________ [1]

(iii) Suggest one purpose of the crust of aluminium oxide.

_______________________________ [1]

(iv) At what temperature does the electrolysis take place?_______________________________ [1]

(ii) What is the formula for aluminium oxide?Al2O3 [1]

(iii) Suggest one purpose of the crust of aluminium oxide.

Keeps heat in/keeps impurities out/stops oxygen reacting with Al [1]

(iv) At what temperature does the electrolysis take place?700-1000°C [1]

(v) Explain why the mixture will only conduct electricity when molten._______________________________ _______________________________ [2]

(vi) Why is it uneconomical to electrolyse pure aluminium oxide?_______________________________ [1]

(v) Explain why the mixture will only conduct electricity when molten.

So that the ions [1] can move [1] and carry electricity

(vi) Why is it uneconomical to electrolyse pure aluminium oxide?

Due to high melting point [1]

(vii) Name the product at the negative electrode and give an ionic equation for its

production.Name of product ____________________Ionic equation ___________________ [3]

(viii)Which electrode must be replaced regularly? Explain your answer using a symbol equation.

Electrode __________________________Equation ________________________ [3]

(vii) Name the product at the negative electrode and give an ionic equation for its

production.Name of product Aluminium [1]Ionic equation Al3+ + 3e- → Al [2]

(viii)Which electrode must be replaced regularly? Explain your answer using a symbol equation.

Electrode Anode [1]Equation C + O2 → CO2 [2]

c) The statue of Eros in London’s

Piccadilly Circus has been in place for about 100 years. It is made of aluminium and has shown virtually no damage from corrosion . Aluminium is used today for overhead electricity cables.

(i) Why is aluminium resistant to corrosion?_______________________________ _______________________________ [3]

(ii) Give one property which aluminium must have if it is used for overhead power

cables._______________________________ [1]

(i) Why is aluminium resistant to corrosion?

protective [1] oxide [1] layer [1] [3] (ii) Give one property which aluminium must

have if it is used for overhead power cables.

Conducts electricity/relatively low density

5a) The following reactions A and B can be classified in different ways.

A copper(II) carbonate → copper (II) oxide + carbon dioxide

B sodium hydroxide + hydrochloric acid → sodium chloride + water

2006, Paper 2

Complete the table by placing a (√) in each column for reactions A and B indicating which terms apply to each reaction. More than one term can be applied to each reaction.

TermReaction

A B

Exothermic

Endothermic

Thermal decomposition

Thermal cracking

Combustion

Neutralisation

Displacement

A copper(II) carbonate → copper (II) oxide + carbon dioxide

B sodium hydroxide + hydrochloric acid → sodium chloride + water

Complete the table by placing a (√) in each column for reactions A and B indicating which terms apply to each reaction. More than one term can be applied to each reaction.

TermReaction

A B

Exothermic √ [1]

Endothermic √ [1]

Thermal decomposition √ [1]

Thermal cracking

Combustion

Neutralisation √ [1]

Displacement

b) Solid copper(II) oxide can be reduced by passing a stream of hydrogen gas over the heated solid.

(i) Write a balanced symbol equation for the reaction between copper(II) oxide and

hydrogen gas._______________________________ [2]

(ii) What would you observe during this reaction?

_______________________________ _______________________________ [2]

(i) Write a balanced symbol equation for the reaction between copper(II) oxide and

hydrogen gas.

CuO + H2 → Cu + H2O [2][1] [1]

(ii) What would you observe during this reaction?

Black [1] solid turns pink/brown [1] flame diminishes in size [1] drops of colourless liquid [1]. Accept condensation. Max [2]

(iii) Write a balanced symbol equation for the hydrogen burning.

_______________________________ [3]

(iii) Write a balanced symbol equation for the hydrogen burning.

2H2 + O2 → 2H2O [3][1] [1] +[1] for balancing

c) The table below gives a series of equations for oxidation and reduction reactions in

two industrial processes.

Reaction Equation Type Industrial Process

A Reduction Aluminium manufacture by electrolysisB 2O2- → O2 + 4e- Oxidation

C S + O2 → SO2 Oxidation Sulphuric Acid manufactureD 2SO2 + O2 → 2SO3 Oxidation

c) The table below gives a series of equations for oxidation and reduction reactions in

two industrial processes.

Reaction Equation Type Industrial Process

A

Al3+ + 3e- → Al [1] [1]+[1] for balancing

ReductionAluminium manufacture by electrolysis

B 2O2- → O2 + 4e- Oxidation

C S + O2 → SO2 Oxidation Sulphuric Acid manufactureD 2SO2 + O2 → 2SO3 Oxidation

(i) Complete the table giving the reduction reaction in the industrial manufacture of aluminium.

(ii) Explain why reaction C is described as oxidation.

_______________________________ _______________________________ [2]

(i) Complete the table giving the reduction reaction in the industrial manufacture of aluminium.

(ii) Explain why reaction C is described as oxidation.

Sulphur gains oxygen [1] gain of oxygen is oxidation [1] [2]

(iii) What is the name of the process for the industrial manufacture of sulphuric acid?

_______________________________ [1]

(iv) Name the catalyst used in reaction D._______________________________ [1]

(iii) What is the name of the process for the industrial manufacture of sulphuric acid?

Contact Process [1]

(iv) Name the catalyst used in reaction D.

Vanadium(V) oxide/vanadium pentoxide/V2O5 [1]

6 Ionic compounds like lead(II) bromide conduct electricity when molten.

a) Explain as fully as possible why ionic compounds conduct electricity when molten.

_______________________________ _______________________________ _______________________________ [2]

2006, Paper 2

6 Ionic compounds like lead(II) bromide conduct electricity when molten.

a) Explain as fully as possible why ionic compounds conduct electricity when molten.

Ions [1] (free to) move/carry charge [1] [2]

b)(i) Draw a labelled diagram of the assembled apparatus used to carry out the electrolysis of molten lead(II) bromide.

[5]

b)(i) Draw a labelled diagram of the assembled apparatus used to carry out the electrolysis of molten lead(II) bromide.

Individual marks are given for correctly labelled and recognisable drawing. Complete circuit with electrodes in molten electrolyte [1] anode/positive electrode

[1], cathode/negative electrode [1], crucible/evaporating basin/beaker, molten lead(II) bromide/electrolyte [1], tripod [1], bunsen burner/heat [1]. (No labels = no marks) (Maximum [5])

(ii) Name the material used to make the electrodes in this electrolysis.

_______________________________ [1]

(iii) What would be observed at the positive electrode during the experiment?

_______________________________ [2]

(ii) Name the material used to make the electrodes in this electrolysis.

Graphite/carbon [1]

(iii) What would be observed at the positive electrode during the experiment?

Red/brown [1] pungent [1] fumes/gas [1] (Maximum [2])

(iv) Name the products of this electrolysis.

_______________________________ [2]

(v) Why does this electrolysis experiment need to be carried out in a fume cupboard?

_______________________________ [2]

(iv) Name the products of this electrolysis.

Lead (metal) [1] bromine [1] [2]

(v) Why does this electrolysis experiment need to be carried out in a fume cupboard?

Toxic [1] nature of bromine/lead [1] [2]

c) The diagram below shows the apparatus used in the refining of copper by electrolysis.

(i) What material is used for the anode?

_______________________________ [2]

(ii) Write a balanced, ionic equation for the reaction which takes place at the anode.

_______________________________ [3]

(i) What material is used for the anode?

Impure [1] copper [1] [2]

(ii) Write a balanced, ionic equation for the reaction which takes place at the anode.

Anode: Cu → Cu2+ + 2e- [3][1] [1] +[1] for balancing

(iii) Name one substance which may be used as the electrolyte.

_______________________________ [1]

(iii) Name one substance which may be used as the electrolyte.

Any soluble copper compounds, usually copper sulphate [1]

3a) A solution of copper(II) sulphate is used as the electrolyte in the refining of copper metal. Impure copper is used as the anode. A piece of pure copper is used as the cathode.

2007, Paper 2

(i) What terms should be used to label the diagram at the points shown?

A _____________________________ [1]B _____________________________ [1]

(ii) Explain what is meant by the term electrolyte.

_______________________________ _______________________________ _______________________________ [3]

(i) What terms should be used to label the diagram at the points shown?

A anode/impure copper [1]B cathode/pure copper [1]

(ii) Explain what is meant by the term electrolyte.

A liquid [1] which conducts electricity [1] and decomposes [1] [3]

(iii) Explain, in terms of the particles involved, why the lamp lights when the circuit is

connected as shown above.

_______________________________ _______________________________ _______________________________ [3]Quality of written communication [2]

(iii) Explain, in terms of the particles involved, why the lamp lights when the circuit is

connected as shown above.

Solution contains ions [1] which can move [1] and carry charge/complete circuit [3]

Quality of written communication [2]

(iv) State one use of copper metal.

_______________________________ [1]

(iv) State one use of copper metal.

(electrical) wiring/plumbing/brass / coinage/roofing/pipes/and any suitable [1]

b) The table below details the changes which occur during the electrolysis of

concentrated sodium chloride solution using titanium electrodes.

(i) Complete the table giving the colour and physical state of the product formed at the anode and give the half equation for the

ionic reaction occurring at the cathode.

Electrode Observations Half Equation

AnodeColour

2Cl- → Cl2 + 2e-

State

CathodeColour Colourless

State Gas

(i) Complete the table giving the colour and physical state of the product formed at the anode and give the half equation for the

ionic reaction occurring at the cathode.

Electrode Observations Half Equation

AnodeColour Green/yellow-

green [1] 2Cl- → Cl2 + 2e-

State Gas [1]

CathodeColour Colourless

2H+ + 2e- → H2 [3]State Gas

(ii) Suggest one reason why titanium is a good material to use for the electrodes

_______________________________ [1]

(ii) Suggest one reason why titanium is a good material to use for the electrodes

conducts electricity / unreactive [1]

c) Aluminium is extracted from its ore by the electrolysis of a molten mixture containing aluminium oxide. The molten mixture

also contains a substance called cryolite which reduces the temperature required from over 2000°C to around 900°C

(i) What is the name of the main ore of aluminium?

_______________________________ [1]

(ii) Write a balanced symbol equation for the production of aluminium and oxygen from aluminium oxide.

_______________________________ [3]

(i) What is the name of the main ore of aluminium?

bauxite [1] [1]

(ii) Write a balanced symbol equation for the production of aluminium and oxygen from aluminium oxide.

2Al2O3 → 4Al + 3O2 [3][1] [1] +[1] for balancing

(iii) State one other purpose of the cryolite in the process.

_______________________________ [1]

(iv) Name one other metal which is extracted from its ore by electrolysis.

_______________________________ [1]

(iii) State one other purpose of the cryolite in the process.

Increases conductivity [1]

(iv) Name one other metal which is extracted from its ore by electrolysis.

Any metal above aluminium in the reactivity series lithium, potassium, sodium, calcium, magnesium [1]

(i) What name did Newlands give to the repeating pattern observed in the properties of the elements?

_______________________________ [1]

(ii) Which group of elements, present in the modern Periodic Table, is missing from Newlands’ table above?

_______________________________ [1]

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