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Electrolysis-Questions

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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
www.chem-exptc.com
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:
A.
B.
C.
D.
Anode
Cathode
Sodium
Sodium
Chlorine
chloride
Chloride
chlorine
Sodium
sodium
4. During the electrolysis of a MOLTEN lead iodide ( PbI 2 ) the product at the anode
and the cathode are:
A.
B.
C.
D.
Anode
Cathode
hydrogen
iodine
lead
lead
iodine
lead
iodide
iodine
5. Circle the correct answer concerning the properties of halogens
Chlorine
Bromine
Iodine
A.
B.
Green, solid
Green, gas
Green, solid
Red brown, gas
Red brown, solid
Pale pink, liquid
C.
Green, liquid
Red brown, liquid
Pale pink, liquid
D.
Green, gas
Red brown, liquid
Pale pink, solid
Electrolysis-Past papers questions
6. During the electrolysis of a CONCENTRATED CuSO4 (aq ) the product at the
CATHODE is:
A.
H 2( g )
B.
O2 ( g )
C.
SO2( g )
D.
Red brown deposit (Cu (s ) )
7. During the electrolysis of a DILUTE CuSO4(aq ) the products at the CATHODE and
the ANODE are:
cathode
anode
A.
O2 ( g )
Cu (s )
B.
H 2( g )
O2 ( g )
C.
Cu (s )
O2 ( g )
D.
Cu (s )
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
+ −
B. Lead(II) bromide
C. Sodium chloride
Carbon electrode
Carbon electrode
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
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
4
Ni
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
2
Lead
In solution
Lead
molten
C.
Sodium
In solution
D.
Sodium
molten
A.
B.
20. Copper and hydrogen can each be formed by electrolysis.
At which electrodes are these elements formed?
copper
hydrogen
anode
anode
anode
cathode
C.
cathode
anode
D.
cathode
cathode
A.
B.
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
type of element formed
A.
negative
metal
B.
negative
non-metal
C.
positive
metal
D.
positive
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
2
3
A.
metal
non-metal
X3Y2
B.
metal
non-metal
X2Y3
C.
non-metal
metal
X3Y2
D.
non-metal
metal
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
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.
chlorine
sodium hydroxide
B.
sodium hydroxide
chlorine
C.
hydrogen
sodium
D.
chlorine
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)
cathode (–ve)
A.
colourless
colourless
B.
colourless
yellow-green
C.
yellow-green
colourless
D.
yellow-green
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
electrode Y
A.
brown gas
silvery metal
B.
brown metal
green gas
C.
green gas
brown metal
D.
silvery metal
brown gas
31. The following electrolysis circuit is set up, using inert electrodes P, Q, R and
S.
+
P
−
+
Q
R
−
S
Molten
Lead (II) bromide
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
+
C
−
B
−
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
Cl 2
B
H2
Cl 2
C
H2
H2
O2
D
H2
Cl 2
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).
brine
X
chlorine
Y
+
positive
electrode
negative
electrode
porous
wall
What are products X and Y?
X
Y
A.
hydrogen
aqueous sodium hydroxide
B.
hydrogen
hydrochloric acid
C.
oxygen
aqueous sodium hydroxide
D.
oxygen
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 ………………..…………..
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 ( 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)
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: …………………..… 
→ …………..……..………...
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 )
A
B
C
1-
D
electrolyte
Name each of the following substances
a) Substance A ………………………………………………..
b) Substance B ……………………………………………………
c) Substance C ………………………………………….………
d) Substance D ………………………………………….………
Electrolysis-Past papers questions
45.
Extraction of Aluminum
+
A
−
B
C
Molten Aluminum
collecting on the bottom
D
(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
+ ……..….
+
……..….

→
….. ZnO +
……. SO 2
+
……. CO 2

→
Zn
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
Anode
(a) Name the products at
−
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 A
Gas B
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
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]
Electrolysis-Past papers questions
51. Calcium may be prepared by the electrolysis of molten calcium chloride
CaCl2 .
Steel Cathode
Graphite anode
+
+
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
Power supply
shows the electrolysis of molten
−
+
potassium bromide.
External Circuit
Electrodes
Molten potassium
bromide
heat
(i)
Draw an arrow on the diagram to show the direction of the
electrons in the external circuit.
(ii)
[1]
Is the following reaction exothermic or endothermic? Give a reason for
your choice.
2KBr

→ 2K + Br2
…………………………………………………………………………………………
………………………………………………………………………………………[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.
Electrolyte
Electrodes
Change at
cathode
Molten
Carbon
Potassium
Bromine
metal formed formed
potassium
bromide
Aqueous
Change
at anode
Change to
electrolyte
Used up
Copper
Stays the same
copper (II)
sulphate
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 −
(ii)
Pb 2+ +

→
……. e − 
→
Br2 + ……… e −
Pb
(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).
………………. - ………………. 
→
[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
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 24− (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
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
iron
electrode
bubbles of
hydrogen form
dilute
sulphuric acid
Which substance in this cell is the reductant and which ion is the oxidant?
reductant ………zinc………………………………………………………
oxidant ………hydrogen ions……………………………………………
(ii)
[2]
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]
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
iodide(aq)
Potassium
manganate(VII)(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 24− (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]
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
[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
Electrolysis-Past papers questions
5. The diagram shows the apparatus used to pass an electric current through concentrated
hydrochloric acid.
chlorine
(a) Label the electrodes.
hydroge
n
[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
(a) Name a suitable material for the inert electrodes.
aqueous
copper(II) sulphate
……………………………… [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
molten
lead bromide
carbon
electrodes
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
rod 2
Voltmeter reading / V
X
2.72
Y
0.78
Z
1.10
magnesium
magnesium
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
electrode 2
(Zinc)
copper
electrode
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
metal
0.78
0.21
0.00
(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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