Electrolysis Questions

Electrolysis-Past papers questions

TAREK S. ELHAGE

2010

IGCSE - CHEMISTRY

Electrolysis questions + past papers questions

www.chem-exptc.com

U A E – A B U D H A B I www.chem-exptc.com


1. During the electrolysis of a MOLTEN salt (compound) the product at the CATHODE is:

A. Non – metal B. Metal C. Sodium D. Chlorine

2. During the electrolysis of a MOLTEN salt (compound) the product at the ANODE is:

A. Non – metal B. Metal C. Sodium D. Chlorine

3. During the electrolysis of a MOLTEN sodium chloride (NaCl ) the product at the

anode and the cathode are:

Anode Cathode

A. Sodium Chloride B. Sodium chlorine C. Chlorine Sodium D. chloride sodium

4. During the electrolysis of a MOLTEN lead iodide ( 2PbI ) the product at the anode

and the cathode are:

Anode Cathode

A. hydrogen iodine B. iodine lead C. lead iodide D. lead iodine

5. Circle the correct answer concerning the properties of halogens

Chlorine Bromine Iodine

A. Green, solid Green, solid Red brown, solid

B. Green, gas Red brown, gas Pale pink, liquid

C. Green, liquid Red brown, liquid Pale pink, liquid

D. Green, gas Red brown, liquid Pale pink, solid


6. During the electrolysis of a CONCENTRATED )(aqCuSO4 the product at the

CATHODE is:

A. )(gH 2

B. )(gO2

C. )(gSO2

D. Red brown deposit( ))(sCu

7. During the electrolysis of a DILUTE )(aqCuSO4 the products at the CATHODE and

the ANODE are:

cathode anode

A. )(gO2 )(sCu

B. )(gH 2 )(gO2

C. )(sCu )(gO2

D. )(sCu )(gSO2

8. The colour of the universal indicator in a neutral medium is .

A. Blue B. Red C. Green D. Violet

9. When a few drops of the universal indicator are added to the acid )(aqHCl , the

expected colour is

A. Blue B. Red C. Green D. Violet

10. An acid reacts with metal to produce

A. Salt + water B. Salt + base C. Salt + hydrogen D. Water + carbon dioxide


11. Name the products of the electrolysis of dilute sulphuric acid

(i) At cathode: ……………………………………. (ii) At anode: ………………………………………

12. Which of the following does NOT contain ions?

(a) Aqueous hydrogen chloride (b) Gaseous hydrogen chloride (c) Solid potassium nitrate (d) Molten potassium chloride

13. Which of the following does NOT contain free ions?

(a) Aqueous hydrogen chloride (b) Aqueous ammonia (c) Solid potassium nitrate (d) Molten potassium chloride

14. When aqueous 4(aq)2SOH solution is electrolysed using inert carbon

electrodes, the substance formed at anode is (a) hydrogen gas (b) Oxygen gas (c) Copper (II) ion (d) Copper deposit

15. When aqueous 4(aq)2SOH solution is electrolysed using inert carbon electrodes, the

substance formed at cathode is: (a) hydrogen gas (b) Oxygen gas (c) Copper (II) ion (d) Copper deposit

16. When aqueous 4(aq)2SOH solution is electrolysed using inert carbon electrodes, the

substance formed at anode is a: (a) Gas that burns with pop sound (b) Gas that relights a glowing splint (c) Brown gas (d) Pink solid


17. The diagram shows the electrolysis of a molten compound X. What is compound X?

A. Copper (II) Chloride

B. Lead(II) bromide

C. Sodium chloride

D. Sodium bromide

18. The diagram shows the electrolysis to electroplate nickel with different metals

Which nickel electrodes are plated with a metal?

A- 1 only

B- 1 and 3 only

C- 2 only

D- 2 and 4 only

electrodeCarbon

gasbrown of bubbles

X compoundMolten

+ −

electrodeCarbon

metalSilvery Molten

heat

Ni Ni Ni Ni1 2 3 4

AqueousChloride sodium

Aqueoussulphate (II)Copper

+ −


19. Metal X is low in the reactivity series and it is liberated by electrolysis of its bromide.

Metal X is ……1…… and the bromide is ……2…… .

Which words correctly complete gaps 1 and 2?

1 2

A.

B.

C.

D.

Lead

Lead

Sodium

Sodium

In solution

molten

In solution

molten

20. Copper and hydrogen can each be formed by electrolysis.

At which electrodes are these elements formed?

copper hydrogen

A.

B.

C.

D.

anode

anode

cathode

cathode

anode

cathode

anode

cathode

21. Two elements X and Y form ionic compounds, XBr2 and Y2O3. The compounds are separately melted and electricity is passed through the liquids.

What are the products at the cathodes?

A. bromine and oxygen

B. bromine and Y

C. oxygen and X

D. X and Y


22. Which change can take place during electrolysis?

A. lead(IV) oxide → lead(II) oxide + oxygen

B. concentrated hydrochloric acid → hydrogen + chlorine

C. sodium hydroxide + nitric acid → sodium nitrate + water

D. lead(II) nitrate + sulphuric acid → lead(II) sulphate + nitric acid

23. What is the charge on an anode and the type of element formed at such an electrode?

charge on anode type of element formed

A.

B.

C.

D.

negative

negative

positive

positive

metal

non-metal

metal

non-metal

24. The diagram shows how to cause a chemical change in a molten compound.

What is this process used for?

A. removal of oxides from metals

B. extraction of metal from its ore

C. neutralisation of industrial waste

D. production of fertilisers

electrodes

compound molten

heat

-+


25. A molten compound is electrolysed. Two atoms of X are deposited at the negative electrode at the same time as three atoms of Y are deposited at the positive electrode.

These results show that:

• X is a …..1..…;

• Y is a …..2..…;

• the formula of the compound is …3… .

How are gaps 1, 2 and 3 correctly completed?

1 2 3

A.

B.

C.

D.

metal

metal

non-metal

non-metal

non-metal

non-metal

metal

metal

X3Y2

X2Y3

X3Y2

X2Y3

26. In which electrolysis are chlorine, hydrogen and sodium hydroxide all produced?

aqueous sodium chloride

molten sodium chloride

A.

B.

C.

D.

27. Metallic and non-metallic elements can both be extracted by electrolysis. Which element is produced at the negative electrode (cathode)?

A. bromine

B. chlorine

C. oxygen

D. hydrogen


28. The electrolysis of concentrated aqueous sodium chloride makes three products.

Which products are shown at the correct electrodes?

anode (+ve)

cathode (–ve)

A.

B.

C.

D.

chlorine

sodium hydroxide

hydrogen

chlorine

sodium hydroxide

chlorine

sodium

hydrogen

29. The diagram shows that two gases are formed when concentrated hydrochloric acid is electrolysed between inert electrodes.

Which line correctly describes the colours of the gases at the electrodes?

anode (+ve) cathode (–ve)

A.

B.

C.

D.

colourless

colourless

yellow-green

yellow-green

colourless

yellow-green

colourless

yellow-green

acid ichydrochloredconcentrat

ve-ve+


30. The diagram shows the electrolysis of molten lead(II) bromide.

What is seen at each electrode? electrode X electrode Y

A.

B.

C.

D.

brown gas

brown metal

green gas

silvery metal

silvery metal

green gas

brown metal

brown gas

31. The following electrolysis circuit is set up, using inert electrodes P, Q, R and S.

At which of the electrodes is a Group VII element produced?

A. P only B. P and R C. Q only D. Q and S

X electrode Yelectrode+ −

heat

bromide )( lead molten II

P Q R S

+ +

Concentrated hydrochloric acid

Molten Lead (II) bromide

− −


32. The following electrolysis circuit is set up, using inert electrodes

At which electrode is a metal deposited?

33. The diagram shown is not complete.

What should be shown at X when the solution has been electrolysed for some time?

X

edconcentratacid ichydrochlor

2Cl 2Cl 2Cl2H 2H 2H 2H2O

A B C D

Molten Lead (II) bromide

Concentrated aqueous sodium chloride

A B C D + +− −


34. Which product is manufactured by electrolysis?

A. aluminium

B. copper(II) sulphate

C. steel

D. sodium chloride

35. The diagram represents the electrolysis of brine (aqueous sodium chloride).

What are products X and Y? X Y

A.

B.

C.

D.

hydrogen

hydrogen

oxygen

oxygen

aqueous sodium hydroxide

hydrochloric acid

aqueous sodium hydroxide

hydrochloric acid

Y

X brine chlorine

+ -

negative electrode

porous wall

positive electrode


36. Define

(a) Electrolysis

………………………………………….…………………..………………………

(b) Electrolyte (liquid)

………………………………………….…………………..……………………

(c) Conductor (metal)

………………………………………….…………………..………………………

(d) Anode

………………………………………….……………………..……………………

(e) Inert electrode

………………………………………….…………………..………………………

37. In electrolysis of molten magnesium chloride 2MgCl using graphite electrodes

(a) Give the formula of the ions present

………………………………………………………………………………………

(b) What is observed at

Anode ……………………………, cathode ……………..……………………

(c) Name the product at

Anode …………………..…………, cathode …………………………..….…

(d) Write the ionic equation to show changes at

Anode: ……………………………… → ……………………………………

Cathode: ……………………………→ ………..…….…………..……..…

(e) Draw a labeled diagram and indicate the direction of electron flow

(f) How are −e removed from outer circuit and where?

……………………………….…………………..…………………………………


38. Name the products at electrodes, during the electrolysis ( using inert electrodes) of

(a) di lute sulphuric acid solution )(42 aqSOH

39. In the electrolysis of molten lead(II) bromide )(2PbBr l using Graphite

electrodes

i . at anode ……………………… , i i . at cathode …………………………

(b) dilute potassium nitrate solution )(3 aqKNO

(i ) at anode ……………………, (i i). at cathode ………………….……

(c) Copper (II) sulphate solution )(4 aqCuSO

i . at anode…………………….…, i i. at cathode ………….………………

(d) concentrated )(aqHCl

at anode …………………………… , i i . at cathode……………….……

(e) Concentrated )(aqNaCl

i . at anode…………………………………………………, ii. at cathode

…………………………………………………

( i) What is observed at anode? ……………………………………………………………………………………....…

( i i ) Name the product at anode? ……………………………………………………………………………………....…

( i i i ) Write the ionic equation that takes place at anode.

…………………………………………………………………. → ……………………………………………………………………………….

( i) What is observed at cathode? ……………………………………………………………………………….

( i i ) Name the product at cathode? ……………………………………………………………………………….

( i i i ) Write the ionic equation that takes place at cathode.

…………………………………………………………………. → ……………………………………………………………………………….


(a) What happens to the ammeter reading if heat is removed? Why?

………………………………………………………………………………………

………………………………………………………………….

(b) How are electrons removed from the outer circuit? and why?

………………………………………………………………………………………

40. In the electrolysis of molten sodium chloride ) gBr( 2M , using inert electrodes

(a) Give the formulae of the ions present:

………………..……….………..

(b) what is observed at each electrode

at anode ………………..…………..

At cathode………………..……..…..

(c) what are the products at the electrodes

at anode ………………..…………..

At cathode………………..……..…..

(d) Write the ionic equation which takes place at

- At Anode: …………..………... → ………………..………...

- At Cathode: …………..…….… → ………………..………...

41. In the electrolysis of sulphuric acid )SO( 4(aq)2H , using inert electrodes

(a) Give the formulae of the ions present: ……………….……...………..

(b) Which ions move to the positive electrode (anode): …………………………..

(c) Which ions move to the negative electrode (cathode): ……………….………..

(d) Name the product at anode: . .……………………………..………..

(e) Write the ionic equation which takes place at

- At Anode: ……..……….…..... → ……….………..………...

(f) Name the product at cathode: ..………………………….………..

(g) Write the ionic equation which takes place at cathode

At Cathode: …………………..… → …………..……..………...


42. The following diagram shows electroplating of a an iron spoon with copper

(a) The metal of which X is made is………………..…………..

(b) Is X made anode or cathode? ……………………….….... .

(c) Is the spoon anode or cathode? ………………………...…

(d) A suitable electrolyte is ……………………….…………………

(e) In case we need to electroplate the spoon with silver,

suggest a suitable

(i) Anode …………………..……..

(ii) Electrolyte ……………………..

43. In purification of copper

(a) Impure copper is made ………………..…………………….………..

(b) Pure copper is made cathode ……………………………….………..

(c) The used electrolyte is ………………..………………………..……..

(d) The formed slime (sludge) has economic importance because

…..……………………..…………………………………………………

……………………………………………………………………..……..

Spoon X

eelectrolyt


4 4 . The diagram shows a method for obtaining pure copper from impure

copper.

1- Name each of the following substances a) Substance A ………………………………………………..

b) Substance B ……………………………………………………

c) Substance C ………………………………………….………

d) Substance D ………………………………………….………

eelectrolyt

positiveElectrode

)( Anode

negativeElectrode

)(cathode

A B

DC


4 5 . E x t r a c t i o n o f A l u m i n u m

(a) Label the letters A to D

(b) Give the name of the main aluminum ore. …………………………………………

(c) Why should aluminum ore be treated with sodium hydroxide before electrolysis?

…………………………………………………………………………………………

…………………………………………………………………………………..………

(d) Name the substance in which aluminum oxide is dissolved in the above

electrolysis process.

………………………………………………………………………………………

(e) Explain why the substance in part (4) is added to aluminum oxide.

………………………………………………………………………………………

………………………………………………………………………………………

(f) Write the balanced ionic equation for the reaction which takes place at the cathode.

………………………………….………………………………………………………

+

−

C B

A

Molten Aluminum

collecting on the bottom D


(g) Which electrode has to be frequently replaced during the process? Explain your

answer.

……………………………………….……………………………………………

…….………………………………………………………………………………

46. Zinc is extracted from its ore, zinc blende ,by reduction with carbon after being roasted with air

a) Complete the following two equations for the reactions involved in this process

….. ZnS + ……..…. → ….. ZnO + ……. 2SO

ZnO + ……..…. → Zn + ……. 2CO

b) Give one use of Zinc. ……………………………………………………

47. (a)Name the 3 products obtained by electrolysis of )(aqKBr using inert electrodes

…………………………………………………………………………..……………………………

(a) How is 2Br obtained from )(aqKBr ?

……………………………………………………..…………….……………………..……………

……………………………………………………..…………..…………..…………..……………

(b) How is 2I obtained from )(aqNaI ?

……...………..……………………………………………………………………………………….…………………………..……


48. In the electrolysis cell of concentrated )(aqNaCl

(a) Name the products at

Anode ……..……………..…., cathode ……….……..………….

(b) Name the solution flows out of the cell.

……………………………………………………………………………

(c) How is sodium hydroxide obtained from concentrated )(aqNaCl ?

………………………………………………………….………………………………

…………………………………………………………..……

…………………………………………………………………………..………………

………….……………………………………………………

(d) How is chlorine gas obtained from )(aqNaCl solution?

…………………………………………………………………………..………………

…………………………………………………………………………..………………

(e) (a) Name the 3 products of the electrolysis of concentrated )(aqKBr .

…………………………………..…..……,

………………………………....…..……….,

………………………….…………………

(f) Write the ionic equations taking place at

(i) anode:……………………..…… → …………………………..……

(ii) Cathode: ……………..…..…… → ………………………..…..……

PorousWall

+ −

)(Brine

(aq)NaClConc.

Anode Cathode


49. Like Copper, nickel can be refined by electrolysis.

Label the diagram to show the purification of nickel in the laboratory

50. The diagram below shows an apparatus in which the electrolysis of aqueous sodium

sulphate containing litmus solution was carried out.

When the current was passed through the solution, the solution around the anode

turned red and the solution around the cathode turned blue. Gas A was found to

relight a glowing splint and gas B, when ignited, burned with “pop”.

(a) Give the formula of the four ions in aqueous sodium sulphate

……………………………………………………….……………………………

……………………………………………………………….………………… [2]

(b) Which ion caused the litmus to turn red?

……………………………………………………………..…………………… [1]

(c) Which ion caused the litmus to turn blue?

……………………………………………………………….………………… [1]

+−

A

Direct

Current

B

Electrodes Platinium

GasGas


(d) (i) Complete the table below

Name of gas Name of electrode at which gas is produced

Gas A

Gas B

(ii) Write an equation to show the formation of gas B.

……………………………………………………….……………………………

……………………………………………………………….……………………

(iii) At which electrode has oxidation taken place?

……………………………………………………….……………………………

……………………………………………………………..………………… [4]

(e) If the experiment is repeated using deionised water without sodium sulphate

dissolved in it, no reaction occurs.

(i) Explain why there is no reaction?

……………………………………………………….……………………………

……………………………………………………………………………………

(ii) Explain why the addition of sodium sulphate to deionised water allows a reaction

to take place.

……………………………………………………….……………………………

………………………………………………………………………….…………

……………………………………………………….……………………………

……………………………………………………………………….………… [2]


51. Calcium may be prepared by the electrolysis of molten calcium chloride

2CaCl .

(i) How would you convert lime (calcium oxide) into anhydrous calcium chloride?

………………………………………….………………………………………………

…………………………………………………………………………………………

(ii) What element are the anodes made from?

…………………………………………………………………………………………

(iii) At which electrode is the calcium obtained?

…………………………………………………………………………………………

(iv) Name the other substance produced during this electrolysis.

……………………………………………………….…………………………………

++−

Graphite anode Graphite anode

Graphite

Molten Calcium

Chloride

Steel Cathode


52. Lithium is extracted by the electrolysis of its molten chloride.

(i) Lithium chloride is an ionic compound. Explain why it conducts electricity in molten state but not in the solid state.

….…………………………………………………………………………….…… [2]

(ii) How is electricity conducted in the part of the circuit labeled

A to B ………………………………………………………………………………

C to D ……………………………………………………………..………………. [2]

(iii) What would be the products of the electrolysis of concentrated aqueous lithium chloride?

……………………………………………………………….………………… [3]

B

−+

D C

A

BA tocircuit ofPart

Electrodes

LithiumMolten chloride

Carbon

DC tocircuit ofPart

heat


53. Chemistry is concerned with the transfer of electrons and energy.

(a) During electrolysis, electrical energy is supplied,

electrons move in the external circuit and ions

move in the electrolyte. The diagram

shows the electrolysis of molten

potassium bromide.

(i) Draw an arrow on the diagram to show the direction of the

electrons in the external circuit. [1]

(ii) Is the following reaction exothermic or endothermic? Give a reason for your choice.

2Br 2K 2KBr +→

…………………………………………………………………………………………

………………………………………………………………………………………[2]

(iii) Electrons are removed from the external circuit. Howe and where is this

done?

…………………………………………………………………………………………

………………………………………………………………………………………[1]

Circuit External

supplyPower

Electrodes

potassiumMolten bromide

heat

+ −


(iv) The results of experiments on electrolysis are shown in the following table.

Complete the table; the first has been completed as an example.

Electrolyte Electrodes Change at cathode

Change at anode

Change to electrolyte

Molten

potassium bromide

Carbon Potassium metal formed

Bromine formed

Used up

Aqueous

copper (II) sulphate

Copper Stays the same

Carbon hydrogen gas evolved

Chlorine formed

Potassium hydroxide formed

[4]

54. The diagram shows the electrolysis of Lead (II) bromide, 2PbBr

(a) Explain why solid lead (II) bromide does not conduct electricity. …………………………………………………..…………………………………

(b) Balance the equations for the reactions that take place at each electrode.

(i) ………... −Br → 2Br + ……… −e

(ii) +2Pb + ……. −e → Pb

(c) Identify the brown fumes shown in the above diagram

…………………………………………………..…………………………………

(d) Define reduction in terms of electrons

…………………………………………………..………………………………

metalSilvery

bromide (II) LeadMolten

fumesBrown

Heat

−+


55. A metallic cup can be coated in silver by electrolysis. The process is called

electroplating

(a) Identify the metal from which the used electrode is made.…………………

(b) Suggest a suitable electrolyte that could be used. ..………………………..

(c) Should the cup be made anode or cathode? ………………………………...

56.

The diagram shows the apparatus used to electrolyse lead(II) bromide.

(a) The wires connected to the electrodes are made of copper.

Explain why copper conducts electricity.

..................................................................................................................

..................................................................................................................

(b) Explain why electrolysis does not occur unless the lead(II) bromide is molten.

...................................................................................................................

...................................................................................................................

(c) The reactions occurring at the electrodes can be represented by the equations shown in the table.

Complete the table to show the electrode (A or B) at which each reaction

occurs, and the type of reaction occurring (oxidation or reduction).

electrode MetalCup

electrolyte


Paper3

57. The electrolysis of concentrated aqueous sodium chloride produces three commercially important chemicals; hydrogen, chlorine and sodium hydroxide.

(a)The ions present are Na+(aq), H+(aq) ,Cl –(aq) and OH–(aq).

(i)Complete the ionic equation for the reaction at the negative electrode (cathode).

………………. + ………………. → [1]

(ii)Complete the ionic equation for the reaction at the positive electrode (anode).

………………. - ………………. → [1]

(iii)Explain why the solution changes from sodium chloride to sodium hydroxide.

……………………………………………………………………………………..………. [1]

(b) (i) Why does the water supply industry use chlorine?

……………………………………………………………………………………..………. [1]

(ii)Name an important chemical that is made from hydrogen.

……………………………………………………………………………………..………. [1]

(iii)Sodium hydroxide reacts with fats to make soap and glycerine

What type of compound are fats?

……………………………………………………………………………………..………. [1]

Nov-2008


1. Copper is purified by electrolysis.

(a) Complete the following.

The positive electrode (anode) is made from……………………………….

The negative electrode (cathode) is made from ……………………………

The electrolyte is aqueous …………………………………………………[3]

(b) Write an ionic equation for the reaction at the positive electrode (anode).

……………………..……………………………………………………..………. [2]

(c) (i) Give two reasons why copper is used,

in electric wiring, ……………………………………………………..

……………………………………………………………………………..………. [2]

in cooking utensils., ……………………………………………………..

……………………………………………………………………………..………. [2]

(ii) Give another use of copper.

……………………………………………………………………………..………. [1]

[Total: 10]

May-2008


1. Zinc is extracted from zinc blende, ZnS. Zinc blende is heated in air to give zinc oxide . part of the zinc oxide reacts with sulphuric acid to give aqueous zinc sulphate. This is electrolysed with inert electrodes (the electrolysis is the same as that of copper (II) sulphate with inert electrodes).

ions present: Zn2+(aq) −24SO (aq) H+(aq) OH-(aq)

(i) Zinc forms at the negative electrode (cathode). Write the equation for this reaction.

………………………………………………………………………..………. [1]

(ii) Write the equation for the reaction at the positive electrode (anode).

………………………………………………………………………..………. [1]

(iii) The electrolyte changes from aqueous zinc sulphate to

………………………………………………………………………..………. [1]

(a) Give two uses of zinc.

1……………...………………………………………………………..……….

2. ………………………….……………………………………..………. [2]

Nov-2007


(a) Cell reactions are both exothermic and redox. They produce electrical

energy as well as heat energy.

(i) The diagram shows a simple cell.

Which substance in this cell is the reductant and which ion is the oxidant?

reductant ………zinc………………………………………………………

oxidant ………hydrogen ions…………………………………………… [2]

(ii) How could the voltage of this cell be increased?

magnesium instead of zinc or increase concentration of acid or copper instead of iron ( increase the reactivity difference)

………………………………………………………………………………..………………[1]

(ii) What is the important large scale use, relating to iron and steel, of this

type of cell reaction?

sacrificial protection or stop iron/steel rusting [1] or galvanising

…………………………………………………………………………………………………[1]

voltmeter

iron electrode

zinc electrode

bubbles of hydrogen form

becomes thinner

dilute sulphuric acid

V


(b) Cells can be set up with inert electrodes and the electrolytes as oxidant

and reductant.

The potassium manganate(VII) is the oxidant and the potassium iodide is the

reductant.

(i) Describe the colour change that would be observed in the left hand beaker.

pink or purple [1] to colourless or decolourised [1] NOT red NOT clear

…………………………………………………………………………………………………[2]

(ii) Write an ionic equation for the reaction in the right hand beaker.

2I– – 2e → I2

…………………………………………………………………………………………………[2]

May-2006

voltmeter

carbon electrode (inert)

carbon electrode (inert)

electron flow

Potassium iodide(aq)

Potassium manganate(VII)(aq)

salt bridge (allows ions to move from one beaker to another)

V


(i) The electrolysis of molten strontium chloride produces strontium metal and

chlorine. Write ionic equations for the reactions at the electrodes.

negative electrode (cathode) …………..…………….………….………

positive electrode (anode) …………..……………………….……… [2]

(ii) One of the products of the electrolysis of concentrated aqueous strontium

chloride is chlorine. Name the other two.

…………..………………………………………………………………… [2]

Nov-2005

( i ) hydrochloric acid [1] ( i i ) Sr 2 + + 2e = Sr [1] 2C l – – 2e = C l 2 [1] or 2C l – = C l 2 + 2e ( i i i ) hydrogen [1] and stront ium hydroxide [1] [2] Nov-2005

(b) Aqueous copper(II) sulphate solution can be electrolysed using carbon electrodes. The ions present in the solution are as follows.

Cu2+(aq), −24SO (aq), H+(aq), OH– (aq)

(i) Write an ionic equation for the reaction at the negative electrode (cathode).

............................................................................................................[1]

(ii) A colourless gas was given off at the positive electrode (anode) and the solution changes from blue to colourless.

Explain these observations.

............................................................................................................

............................................................................................................[2]

(c) Aqueous copper(II) sulphate can be electrolysed using copper electrodes. The reaction at the negative electrode is the same but the positive electrode becomes smaller and the solution remains blue.

(i) Write a word equation for the reaction at the positive electrode.

............................................................................................................[1]


(ii) Explain why the colour of the solution does not change.

............................................................................................................

............................................................................................................[2]

(iii) What is the large scale use of this electrolysis?

............................................................................................................[1]

May-2004

(b) (i) Cu2+ + 2e = Cu [1] (ii) gas is oxygen [1] (copper(II) sulphate) changes to sulphuric acid [1] or copper ions removed from solution (c) (i) copper atoms - electrons = copper ions [1] accept correct symbol equation (ii) concentration of copper ions does not change or [1] amount or number of copper ions does not change copper ions are removed and then replaced [1] or copper is transferred from anode to cathode (iii) refining copper or plating (core) [1] or extraction of boulder copper

May-2004


1. Copper is purified by electrolysis.

(a) Complete the following.

The positive electrode (anode) is made from………………………………….

The negative electrode (cathode) is made from …………………..…………

The electrolyte is aqueous ………………… ………………………………[3]

(b) Write an ionic equation for the reaction at the positive electrode (anode).

…………………….………………………………...………………..………. [2]

(c) (i) Give two reasons why copper is used,

in electric wiring, …………………………………..……………………..

……………………………………………………………………..………. [2]

in cooking utensils., …………………………..………………………..

……………………….……………………………………………..………. [2]

(ii) Give another use of copper.

……………………………………………………………………..………. [1]

[Total: 10]

May-2008


2. Lead bromide was placed in a tube and connected to an electrical circuit as shown below.

The lead bromide was heated until molten. A brown gas was given off.

(a) State one other expected observation. ………………………………………….……………………….………………………………[1]

(b) (i)Suggest a suitable material to make the electrodes.

…………..………………………….……………………………….………………………….[1]

(ii)Indicate on the diagram the negative electrode (cathode). [1]

(c) Name the brown gas. At what electrode will the gas be given off?

⋅ Name …………………..………………….…………………………………….…………

⋅ electrode ……………………………….………………………………...………………[2]

(d) Why is this experiment carried out in a fume cupboard?

…………..………………………….……………………………….…………………………[1]

May-June - 2004

d.c.power supply

LEAD BROMIDE

TOXIC

bulb

heat


3. The diagram shows the apparatus used to find out the effect of an electric current on a concentrated aqueous solution of sodium chloride.

(a) On the diagram label the electrodes [1]

(b) Give three observations when the circuit is switched on.

1……………………….…………………………………………………………………………

2……………………….…………………………………………………………………………

3……………………….……………………………………………….………………………[3]

(c) (i)Name the product at the positive electrode (anode).

……………………….……………………………………….…………………………………[1]

(ii)State a test for this product and the result of the test.

test……….……………………………………….………………………………………[1]

result ……………………….………………………………………………………………[1]

May-June-2006


4. Impure copper is extracted from the ore. This copper is refined by electrolysis.

(a) Name;

the material used for the positive electrode (anode),

……………………..…………………………………………….……..………. [1]

the material used for the negative electrode (cathode),

…………………………………………………………………….………………[1]

a suitable electrolyte.

…………………………………………………………………….………………[1]

(b) Write an ionic equation for the reaction at the negative electrode.

…………………………………………………………………….………………[1]

(c) One use of this pure copper is electrical conductors, another is to make alloys.

Name the metal that is alloyed with copper to make brass.

…………………………………………………………………….………………[1]

Nov-2005


5. The diagram shows the apparatus used to pass an electric current through concentrated hydrochloric acid.

(a) Label the electrodes. [1]

(b) Give two observations when the current is switched on. 1……….…………………………………..…………………………………………….

2……….…………………………………..………………………………………… [2]

(c) Give a test for the product at the negative electrode (cathode). test ……….…………………………..……………………………………………. result ……….………………..……………………………………………………. [2]

oct-Nov-2005

chlorine hydroge

n


6. Electricity was passed through a concentrated solution of sodium chloride containing Universal Indicator .

(a) Suggest a suitable material for the electrodes.

carbon/graphite/any unreactive metal e.g. platinum/nickel………………….………..[1]

Three observations were noted:

1- Bubbles of gas seen immediately at the negative electrode.

2- Bubbles of gas formed after some time at the positive electrode.

3- The solution turned blue around the negative electrode and colourless near the positive electrode.

(b) Give a test to show that the gas observed in 1 is hydrogen.

• Test ……lighted splint (1) ……………..……………….……..[1]

• result … pops(1) ………………………………………………..[1]

(c) Suggest why bubbles of gas were not seen immediately in 2.

gas dissolves (in the solution) o.w.t.t.e [1]…………………………..………………..

………………………………………………………………………………………………..[2]

(d) (d)What causes the colour change in 3 at

the negative electrode, …alkali/(sodium) hydroxide (1)………………………………..[1]

the positive electrode? …chlorine/bleach (1) not chloride or chlorine ions………..[1]

Concentrated aqueous sodium chloride and universal indicator

negative electrode

positive electrode

carbon rods

+ −


7. A constant current was passed through aqueous copper(II ) sulphate using inert electrodes as shown in the diagram below. Copper was deposited at one of the electrodes.

A variable resistor

+ – D E

aqueous copper(II ) sulphate

(a) Name a suitable material for the inert electrodes. ……………………………… [1]

(b) At which electrode was copper deposited, D or E? ……………………………… [1]

(c) What was seen at the other electrode?

............................................................................................................................................[1]

(d) What was the colour of the electrolyte

(i) at the start of the experiment,

...................................................................................................................................

(ii)at the end of the experiment?

................................................................................................................................... [2]


8. A metal cup can be coated in silver by electrolysis. The cup must be very clean and also rotated during the process, which is known as electroplating.

(a) Should the metal cup be the anode or the cathode?

.............................................................................................................................[1]

(b)Identify the metal from which the electrode is made.

..............................................................................................................................[1]

(c) Suggest a suitable electrolyte that could be used to electroplate this cup.

..............................................................................................................................[2]

(d)Suggest why the cup must be

(ii) very clean, ...........................................................................................................................

......................................................................................................................[1]

(iii) rotated during the electrolysis. ...........................................................................................................................

......................................................................................................................[1]

2 (a) cathode / negative [1] (b) silver [1] (c) silver nitrate (1) solution (1) [2] // any silver salt not Cl -, I- (d) (i) silver will not coat / stick or similar [1] (ii) to give even coating / all of it gets coated [1] [Total 6]

electrolyte

metal electrode

cup


9. A student electrolysed lead bromide and aqueous sodium chloride in the apparatus shown below.

Each of the electrodes is labelled with a letter.

(a) Why was it necessary for lead bromide to be molten?

......................................................................................................................................[1]

(b) (i)What was produced at electrode A?

...................................................................................................................................

(ii) What was the appearance of this product?

...................................................................................................................................

(iii) What was produced at electrode B?

...................................................................................................................................

(iv) Where did this product collect?

................................................................................................................................... [4]

D C B A

+ -

carbon electrodes

carbon electrodes

molten lead bromide

aqueous sodium chloride

heat

+ - + -


(c) Gases were produced at electrodes C and D. In each case name the gas and give a test to confirm its presence.

(i) the gas produced at C ...............................................................................

test for this gas .........................................................................................................

(ii) gas produced at D ,,....................................................................................

test for this gas ......................................................................................................... [4]

(d) What change should be made so that sodium is produced at one of the electrodes?

..........................................................................................................................................[1]


10. The apparatus below was used to electrolyse water.

(a) (i) Why was a small volume of sulphuric acid added to the water?

.......................................................................................................................

(ii) Name the gas collected in tube X and give a test for this gas.

gas ............................................................................................................................

test ............................................................................................................................

(iii) Name the gas collected in tube Y and give a test for this gas.

gas ............................................................................................................................

test ........................................................................................................................[5]

(aq)SOH 42

electrodes graphite

YX


(b) State how the volume of gas collected in tube X compares with the volume of gas collected in tube Y.

..................................................................................................................................... [1]

(c) Name a gas that may be used to sterilise water and give a test for this gas.

gas ...................................................................................................................................

test .............................................................................................................................. [2]

(d) A student added a small piece of sodium and a small piece of iron to separate samples

of water. What observations were made?

sodium ..............................................................................................................................

..........................................................................................................................................

iron ...................................................................................................................................

..................................................................................................................................... [3]


11. A student electrolysed concentrated aqueous sodium chloride using the apparatus below.

The solution also contained litmus solution.

(a) (i)Name the gas produced at the anode (positive electrode).

......................................................................................................................................... [1]

(ii) Suggest what happened to the colour of the solution around the anode as the

electrolysis proceeded.

…..………......................................................................................................................... [1]

(iii) Why did this change take place?

…….……….................................................................................................................... [1]

(b) (i)Name the gas produced at the cathode (negative electrode).

..................................................................................................................................... [1]

(ii) Give a test for this gas.

........................................................................................................................................ [1]

Carbon

anode

Carbon

anode

aqueous sodium

chloride containing

some litmus solution

+ -


(iii) What happened to the colour of the solution around the cathode as the electrolysis

proceeded?

.............................................................................................................................. [1]

(iv) Why did this change take place?

.............................................................................................................................. [1]

(c) The solution was replaced by a dilute solution of an acid. Suggest which acid would produce the same gases as those produced with concentrated aqueous sodium chloride.

(d) Under what conditions does the electrolysis of sodium chloride produce sodium at one of

the electrodes?

[Total: 9]


12. The diagram shows a cell that can be used to make electrical energy.

(a) Explain why distilled water is not used as the electrolyte.

............................................................................................................................................[1]

(b) This table shows the results when rods of three metals, X, Y and Z, are used in separate

experiments. All the metals are less reactive than magnesium.

Place the metals in order of reactivity most reactive magnesium

………………………

………………………

least reactive ………………………

rod 1 rod 2 Voltmeter reading / V magnesium X 2.72

magnesium Y 0.78

magnesium Z 1.10

Magnesium

rod

voltmeter

rod of metal X, Y or Z

electrolyte


(c) A student places a rod of magnesium in aqueous silver nitrate.

(i) Write an ionic equation, with state symbols, for the reaction which happened.

...................................................................................................................................

(ii) What would you expect to see after the reaction had been taking place for some time?

...............................................................................................................................................

...........................................................................................................................................[3]


13. This reaction can be used to generate electricity in a cell.

(a) Write an ionic equation for the reaction between zinc and aqueous copper(II) sulphate.

..................................................................................................................................... [1]

(b) Drawn an arrow on the diagram to show the direction of the flow of electrons in the wire. [1]

(c) The voltage of the cell was measured when the following metals were used as electrode 2.

copper iron lead zinc

Complete the table by entering the metals in the correct order.

(d) When metal M was used as electrode 2, it produced a higher voltage than zinc. Suggest a name for metal M.

........................................................................................................................................................ [1]

meter reading / V metal

1.10

0.78

0.21

0.00

copper

electrode

electrode 2

(Zinc)

aqueous copper (II) sulphate

V


14. The diagram shows a cell for purifying copper.

(a) Describe what you would observe during this electrolysis and write the equations for the reactions at the electrodes.

(b) The electrodes and the electrolyte conduct electricity. (i) Explain how the structure of metals allows copper electrodes to conduct electricity. [1]

(ii) Explain why solid copper(II) sulphate does not conduct electricity but an aqueous

solution of copper(II ) sulphate does conduct.

(c) Describe how the apparatus shown in the diagram could be modified in order to electroplate

an iron object, such as a knife, with nickel.

(d) Bronze is an alloy of copper and tin. Bronze is less malleable than pure copper. Use ideas

about the structure of metals and alloys to explain why bronze is less malleable than pure copper.

Pure copper

cathode

impure copper

anode

Electrolyte (aqueous copper (II)

sulphate

+ -


15. An electric current can be generated by a simple electrochemical cell such as the one shown.

(a) Explain why the flow of electrons is in the direction shown in the diagram. [2]

(b) Suggest why silver nitrate would not be a good electrolyte to use in this cell. [1]

magnesium copper

Electrolyte (magnesium sulphate)

V

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Electrolysis Questions