electrolysis worksheet-igcse (2)
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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
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Electrolysis-Past papers questions
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
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Electrolysis-Past papers questions
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
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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) 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
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Electrolysis-Past papers questions
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
+
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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 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
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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 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
-+
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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 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
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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)
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+
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Electrolysis-Past papers questions
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
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Electrolysis-Past papers questions
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 + +
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Electrolysis-Past papers questions
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
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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 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? ...
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Electrolysis-Past papers questions
38. Name the products at electrodes, during the electrolysis ( using inert electrodes) of
(a) dilute sulphuric acid solution )(42 aqSOH
39. In the electrolysis of molten lead(II) bromide )(2PbBr l using Graphite electrodes
i . at anode , ii . 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., ii. at cathode .
(d) concentrated )(aqHCl
at anode , ii . 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.
. .
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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 ) 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: .. .......
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Electrolysis-Past papers questions
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
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Electrolysis-Past papers questions
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
)( Anodenegative
Electrode)(cathode
A B
DC
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Electrolysis-Past papers questions
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
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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 + . 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 ? ........
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Electrolysis-Past papers questions
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
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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.
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
-
Electrolysis-Past papers questions
(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]
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Electrolysis-Past papers questions
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
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Electrolysis-Past papers questions
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
ABA tocircuit ofPart
Electrodes
LithiumMolten chloride
Carbon
DC tocircuit ofPart
heat
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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.
(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
+
-
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.
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
+
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Electrolysis-Past papers questions
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
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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).
. - . [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
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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
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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) 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
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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.
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
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Electrolysis-Past papers questions
(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
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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 ) hydrochloric acid [1] ( i i ) Sr 2 + + 2e = Sr [1] 2C l 2e = C l2 [1] or 2C l = C l2 + 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]
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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
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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
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Electrolysis-Past papers questions
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
-
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 [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
-
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
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Electrolysis-Past papers questions
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
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Electrolysis-Past papers questions
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
+
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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]
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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.
(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
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Electrolysis-Past papers questions
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
+ - + -
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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]
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Electrolysis-Past papers questions
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
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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]
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Electrolysis-Past papers questions
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
+ -
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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]
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Electrolysis-Past papers questions
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
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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]
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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]
(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
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Electrolysis-Past papers questions
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
+ -
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Electrolysis-Past papers questions
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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