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TAREK S. ELHAGE

Electrolysis-Past papers questions

IGCSE - CHEMISTRY

Electrolysis questions + past papers questions

www.chem-exptc.com

2010

UAE ­ ABU DHABI

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Electrolysis-Past papers questions

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

is: A. B. C. D. Non ­ metal Metal Sodium Chlorine

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

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

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

anode and the cathode are: Anode A. B. C. D. Sodium Sodium Chlorine chloride Cathode Chloride chlorine Sodium sodium

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

and the cathode are: Anode A. B. C. D. hydrogen iodine lead lead Cathode iodine lead iodide iodine

5. Circle the correct answer concerning the properties of halogens

Chlorine A. B. C. D. Green, solid Green, gas Green, liquid Green, gas Bromine Green, solid Red brown, gas Red brown, liquid Red brown, liquid Iodine Red brown, solid Pale pink, liquid Pale pink, liquid Pale pink, solid

Electrolysis-Past papers questions

6. During the electrolysis of a CONCENTRATED CuSO4 (aq ) the product at the

CATHODE is: A. B. C. D.

H 2( g ) O2 ( g )

SO2( g )

Red brown deposit (Cu (s ) )

7. During the electrolysis of a DILUTE CuSO4(aq ) the products at the CATHODE and

the ANODE are: cathode A. B. C. D.

O2 ( g ) H 2( g ) Cu (s ) Cu (s )

anode

Cu (s ) O2 ( g ) O2 ( g ) SO2( g )

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

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

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

expected colour is A. Blue B. Red C. Green D. Violet 10. An acid reacts with metal to produce A. B. C. D. Salt + water Salt + base Salt + hydrogen Water + carbon dioxide

Electrolysis-Past papers questions

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

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

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

14. When aqueous H 2 SO 4(aq) 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 H 2 SO 4(aq) 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 H 2 SO 4(aq) 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

Electrolysis-Past papers questions

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

What is compound X? A. Copper (II) Chloride

+ -

Carbon electrode Carbon electrode

B. Lead(II) bromide C. Sodium chloride D. Sodium bromide

bubbles of brown gas Molten compound X

Molten Silvery metal

heat

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

+ -

1 Ni 2 Ni 3 Ni 4 Ni

Aqueous Copper (II) sulphate

Which nickel electrodes are plated with a metal? A- 1 only B- 1 and 3 only C- 2 only D- 2 and 4 only

Aqueous sodium Chloride

Electrolysis-Past papers questions

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 A. B. C. D. Lead Lead Sodium Sodium 2 In solution molten In solution molten

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

At which electrodes are these elements formed? copper A. B. C. D. anode anode cathode cathode hydrogen 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

Electrolysis-Past papers questions

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 A. B. C. D. negative negative positive positive type of element formed metal non-metal metal non-metal

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

+

-

electrodes

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

heat

Electrolysis-Past papers questions

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 A. B. C. D. metal metal non-metal non-metal 2 non-metal non-metal metal metal 3 X3Y2 X2Y3 X3Y2 X2Y3

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

produced? aqueous sodium chloride A. B. C. D. molten sodium chloride

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

Electrolysis-Past papers questions

28. The electrolysis of concentrated aqueous sodium chloride makes three

products. Which products are shown at the correct electrodes? anode (+ve) A. B. C. D. chlorine sodium hydroxide hydrogen chlorine cathode (­ve) sodium hydroxide chlorine sodium hydrogen

29. The diagram shows that two gases are formed when concentrated

hydrochloric acid is electrolysed between inert electrodes.

+ve

- ve

concentrated hydrochloric acid

Which line correctly describes the colours of the gases at the electrodes? anode (+ve) A. B. C. D. colourless colourless yellow-green yellow-green cathode (­ve) colourless yellow-green colourless yellow-green

Electrolysis-Past papers questions

30.

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

electrode X +

- electrode Y

molten lead ( II) bromide

heat

What is seen at each electrode?

electrode X A. B. C. D. brown gas brown metal green gas silvery metal

electrode Y silvery metal green gas brown metal brown gas

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

S.

+

-

+

-

P Molten Lead (II) bromide

Q

R

S Concentrated hydrochloric acid

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

Electrolysis-Past papers questions

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

At which electrode is a metal deposited?

+ A

-

B

+ C

-

D Molten Lead (II) bromide

Concentrated aqueous sodium chloride

33.

The diagram shown is not complete.

X

concentrated

hydrochlor ic acid

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

Cl 2

H2

Cl 2

H2

H2

O2

H2

Cl 2

Electrolysis-Past papers questions

34. Which product is manufactured by electrolysis?

A. B. C. D. aluminium copper(II) sulphate steel sodium chloride

35.

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

Y

+ positive electrode

What are products X and Y?

porous wall negative electrode

X A. B. C. D. hydrogen hydrogen oxygen oxygen

Y aqueous sodium hydroxide hydrochloric acid aqueous sodium hydroxide hydrochloric acid

Electrolysis-Past papers questions

36. Define

(a)Electrolysis ................................................................................................... (b) Electrolyte (liquid) ................................................................................................ (c)Conductor (metal) ................................................................................................... (d) Anode ................................................................................................... (e)Inert electrode ...................................................................................................

37. In electrolysis of molten magnesium chloride MgCl2 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 dia gram and indicat e the direction of electron flow

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

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

Electrolysis-Past papers questions

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

(a) dilute sulphuric acid solution H 2 SO4 ( aq )

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

(b) dilute potassium nitrate solution KNO3( aq )

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

(c) Copper (II) sulphate solution CuSO4 ( aq )

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

(d) concentrated HCl ( aq )

at anode ................................. , ii. at cathode.........................

(e) Concentrated NaCl( aq )

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

39. In the electrolysis of molten lead(II) bromide PbBr2(l ) using Graphite

electrodes

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

(ii) Name the product at anode? ................................................................................. (iii)

Write the ionic equation that takes place at anode.

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

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

(ii) Name the product at cathode? .............................................................................. (iii)

Write the ionic equation that takes place at cathode.

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

Electrolysis-Past papers questions

(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 ( M gBr 2 ) , using inert electrodes

(a) Give the formulae of the ions present: ......................................... (b) what is observed at each electrode at anode .................................. (c) what are the products at the electrodes at anode .................................. At cathode................................. At cathode.................................

(d) Write the ionic equation which takes place at

- At Anode: .......................... ................................ - At Cathode: ........................ ................................

41. In the electrolysis of sulphuric acid ( H 2 SO 4(aq) ) , 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) (e) Name the product at anode: ................................................ Write the ionic equation which takes place at

- At Anode: .......................... .................................

(f)

(g)

Name the product at cathode: ............................................

Write the ionic equation which takes place at cathode

At Cathode: .......................... ..................................

Electrolysis-Past papers questions

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

(a) The metal of which X is m ade 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) Electrol yte ..........................

Spoon

X

electrolyte

43. In purification of copper

(a) Impure copper is made ........................................................ (b) Pure copper is made cathode ................................................ (c) The used electrol yte is ......................................................... (d) The formed slime (sludge) has economic importance because ........................................................................................ ........................................................................................

Electrolysis-Past papers questions

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

copper.

positive Electrode ( Anode )

negative Electrode ( cathode )

B

A

1-

D electrolyte Name each of the following substances a) Substance A ........................................................

b) Substance B ............................................................ c) Substance C .......................................................... d) Substance D ..........................................................

C

Electrolysis-Past papers questions

45.

Extraction of Aluminum

+

-

C

A

B

D

Molten Aluminum collecting on the bottom

(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.

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

Electrolysis-Past papers questions

(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 +

....... SO 2

ZnO

+

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

Zn

+

....... CO 2

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

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

(a) How is Br 2 obtained from KBr ( aq ) ? ....................................................................................................................... ....................................................................................................................... (b) How is I 2 obtained from NaI ( aq ) ?

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

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

Electrolysis-Past papers questions

48. In the electrolysis cell of concentrated NaCl (aq )

(Brine)

Conc. NaCl (aq)

+

Porous Wall

-

(a) Name the products at

Anode

Cathode

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

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

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

(c)How is sodium hydroxide obtained from concentrated NaCl (aq ) ?

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

(d) How is chlorine gas obtained from NaCl (aq ) solution?

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

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

...................................................., ......................................................., ....................................................

(f) Write the ionic equations taking place at

(i) anode:................................ (ii) Cathode: ............................

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

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

Electrolysis-Past papers questions

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.

Gas B

Gas A Platinium Electrodes

Direct Current

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]

Electrolysis-Past papers questions

(d) (i) Complete the table below

Name of gas

Gas A Gas B

Name of electrode at which gas is produced

(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]

Electrolysis-Past papers questions

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

CaCl2 .

Graphite anode Steel Cathode

+

-

+

Graphite anode

Molten Calcium Chloride

Graphite

(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.

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

Electrolysis-Past papers questions

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

+ -

A

Part of circuit A to B

Carbon Electrodes

B

Part of circuit C to D

D

C

Molten Lithium chloride

heat

(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]

Electrolysis-Past papers questions

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.

External Circuit Electrodes Power supply

+

-

Molten potassium bromide

heat

(i) (ii) Draw an arrow on the diagram to show the direction of the electrons in the external circuit. Is the following reaction exothermic or endothermic? Give a reason for your choice.

2KBr 2K + Br2

[1]

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

(iii)

Electrons are removed from the external circuit. Howe and where is this done?

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

Electrolysis-Past papers questions

(iv)

The results of experiments on electrolysis are shown in the following table. Complete the table; the first has been completed as an example. Electrodes Carbon Change at cathode Change at anode Change to electrolyte Used up

Electrolyte Molten potassium bromide Aqueous copper (II) sulphate

Potassium Bromine metal formed formed

Copper

Stays the same

Carbon

hydrogen gas evolved

Chlorine formed

Potassium hydroxide formed [4]

54.

The diagram shows the electrolysis of Lead (II) bromide, PbBr2

+

Brown fumes

-

Silvery metal Molten Lead (II) bromide

Heat

(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 -

Pb 2+ +

Br2 + ......... e -

Pb

(ii)

....... e -

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

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

(d) Define reduction in terms of electrons

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

Electrolysis-Past papers questions

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

electroplating

Cup

Metal electrode

electrolyte

(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).

Electrolysis-Past papers questions

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). ................... - ................... (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] [1]

Nov-2008

Electrolysis-Past papers questions

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

Electrolysis-Past papers questions

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) SO 2- (aq) H+(aq) OH-(aq) 4 (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

Electrolysis-Past papers questions (a) Cell reactions are both exothermic and redox. They produce electrical energy as well as heat energy. (i) The diagram shows a simple cell.

voltmeter

V

zinc electrode becomes thinner dilute sulphuric acid

iron electrode bubbles of hydrogen form

Which substance in this cell is the reductant and which ion is the oxidant? reductant .........zinc............................................................... oxidant .........hydrogen ions................................................... (ii) How could the voltage of this cell be increased? [2]

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]

Electrolysis-Past papers questions (b) Cells can be set up with inert electrodes and the electrolytes as oxidant and reductant.

voltmeter

V

electron flow carbon electrode (inert) carbon electrode (inert)

Potassium manganate(VII)(aq)

Potassium iodide(aq)

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

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

Electrolysis-Past papers questions (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) h ydroc hloric acid [1] (ii) Sr 2 + + 2e = Sr [1] 2C l ­ ­ 2e = C l 2 [1] or 2C l ­ = C l 2 + 2e (iii ) hydr ogen [1] and stront ium hydr oxi de [ 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),

SO 2- (aq), 4

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]

Electrolysis-Past papers questions (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

Electrolysis-Past papers questions

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

Electrolysis-Past papers questions

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

d.c.power supply

bulb

LEAD BROMIDE TOXIC

heat 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

Electrolysis-Past papers questions

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

[1]

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

Electrolysis-Past papers questions

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

Electrolysis-Past papers questions

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

chlorine

hydroge n

(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

Electrolysis-Past papers questions

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

positive electrode

+

carbon rods

-

negative electrode

Concentrated aqueous sodium chloride and 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]

Electrolysis-Past papers questions 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]

Electrolysis-Past papers questions 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.

metal electrode

cup electrolyte

(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]

Electrolysis-Past papers questions 9. A student electrolysed lead bromide and aqueous sodium chloride in the apparatus shown below.

+ -

+

A B

-

carbon electrodes

+

C D

-

carbon electrodes

molten lead bromide

aqueous sodium chloride

heat 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]

Electrolysis-Past papers questions

(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]

Electrolysis-Past papers questions 10. The apparatus below was used to electrolyse water.

X

Y

graphite electrodes

H 2SO 4 (aq)

(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]

Electrolysis-Past papers questions

(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]

Electrolysis-Past papers questions 11. A student electrolysed concentrated aqueous sodium chloride using the apparatus below. The solution also contained litmus solution. + -

Carbon anode

Carbon anode

aqueous sodium chloride containing some 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]

Electrolysis-Past papers questions

(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]

Electrolysis-Past papers questions

12.

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

voltmeter

rod of metal X, Y or Z

Magnesium rod

electrolyte

(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. rod 1 magnesium magnesium magnesium rod 2 X Y Z Voltmeter reading / V 2.72 0.78 1.10

Place the metals in order of reactivity most reactive

magnesium ........................... ...........................

least reactive

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

Electrolysis-Past papers questions

(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]

Electrolysis-Past papers questions

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]

V

copper electrode

electrode 2 (Zinc)

aqueous copper (II) sulphate

(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. meter reading / V 1.10 0.78 0.21 0.00 metal

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

Suggest a name for metal M.

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

Electrolysis-Past papers questions

14. The diagram shows a cell for purifying copper.

+

Pure copper cathode

impure copper anode

Electrolyte (aqueous copper (II) sulphate

(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.

Electrolysis-Past papers questions

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

V

magnesium

copper

Electrolyte (magnesium sulphate)

(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]

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