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Chemistry extension edexcel > C3.3 Electrolytic processes > Flashcards

C3.3 Electrolytic processes Flashcards

1
Q

How do you break the bonds in an ionic solid?

A

By melting it or dissolving it in water

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2
Q

What are electrolytes?

A

Ionic substances that conduct electricity when molten or in aqueous solution

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3
Q

Why do ionic substances have to be molten or in aqueous solution in order to conduct electricity?

A

Because then the ions are able to move freely

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4
Q

What is electrolysis?

A

The chemical decomposition of a compound produced by passing an electric current through a liquid or solution containing ions

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5
Q

What electrical supply does electrolysis use?

A

DC (direct current)

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6
Q

What things are necessary to carry out electrolysis?

A
  • a DC electricity supply
  • two electrodes
  • an electrolyte
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7
Q

What forces cause ions to move towards electrodes with opposite charges during electrolysis?

A

Electrostatic forces of attraction

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8
Q

What charge does a cathode have?

A

Negative

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9
Q

What charge does an anode have?

A

Positive

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10
Q

What charge does a cation have?

A

Positive

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11
Q

What charge does an anion have?

A

Negative

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12
Q

During the electrolysis of copper chromate solution what colour solution does the chromate form?

A

Orange-brown

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13
Q

During the electrolysis of copper chromate solution what colour solution do the copper ions form?

A

Blue

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14
Q

What are electrodes made out of?

A

Metal or carbon

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15
Q

What happens to ions at the cathode?

A

Electrons from the negative cathode are transferred to the positive ions

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16
Q

What happens to ions at the anode?

A

The negative ions lose electrons to the positively charged anode

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17
Q

What is reduction?

A

When positive ions gain electrons

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18
Q

What is oxidation?

A

The loss of electrons by a negative ion

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19
Q

Why do chemical changes occur at the electrodes?

A

Because the transfer of electrons that happens there changes ions into atoms or molecules

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20
Q

During the electrolysis of sodium chloride, what ions are attracted to the cathode?

A

Sodium ions

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21
Q

In the electrolysis of sodium chloride, what ions are attracted to the anode?

A

Chloride ions

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22
Q

What is produced from the electrolysis of NaCl?

A

Sodium metal and chlorine gas

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23
Q

What are the uses of sodium?

A

In street lamps and as a coolant in nuclear reactions

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24
Q

How is sodium used in street lamps?

A

Sodium vapour gives out a bright yellow light when an electric current is passed through it

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25
Q

How is sodium used as a coolant in nuclear reactions?

A

Liquid sodium metal has a high thermal conductivity and transfers heat very efficiently from the core of the reactor to water, which then turns into steam and drives the generators

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26
Q

What does a half-equation for electrolysis show?

A

The change at just one of the electrodes

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27
Q

Why is hydrogen a clean fuel?

A
  • it doesn’t produce any of the pollutants that fossil fuels produce
  • it doesn’t produce carbon dioxide
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28
Q

What does it mean when a material is inert?

A

It won’t react

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29
Q

Why does an electrode need to be made from an inert material?

A

So that it doesn’t react with the electrolyte or the products during electrolysis

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30
Q

How can you measure the rate of reaction of gases during electrolysis?

A

Test tubes can collect the gases from the electrode, and the amount of time it takes for them to fill up and can show the rate of reaction

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31
Q

What does Hoffman’s voltameter do?

A

Collect gases given off during electrolysis so that the volume can be read from the vertical tubes

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32
Q

What happens to the ions in a molten salt when it is electrolysed?

A

They become discharged as atoms or molecules at the electrodes

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33
Q

Why is an ion converted back to an element when it is discharged?

A

The loss or gain of electrons means that the number of electrons is back to being the same as the number of protons like in the original element

34
Q

During the electrolysis of water, where is hydrogen produced?

A

At the cathode

35
Q

What needs to be done to a salt before it is electrolysed?

A

It needs to dissociate into ions

35
Q

What happens to the ionic bonds in a salt when it dissociates?

A

They break

35
Q

During the electrolysis of lead bromide, what is produced at the anode?

35
Q

What form is the bromine produced from the electrolysis lead bromide in?

35
Q

What does the bromine produce from the electrolysis of lead bromide look like?

A

A brown vapour

36
Q

What form is the lead metal produced from the electrolysis of lead bromide in?

A

Molten (liquid)

37
Q

What is produced at the cathode during the electrolysis of lead bromide?

A

Lead metal

38
Q

Why are hydroxide ions discharged at the anode instead of sulphate during the electrolysis of copper sulphate?

A

Hydroxide ions lose electrons more readily than sulphate ions

39
Q

What is produced at the cathode during the electrolysis of sodium sulphate?

A

Hydrogen gas

40
Q

What is produced at the anode during the electrolysis of sodium sulphate?

A

Water and oxygen

41
Q

What does it mean when a material is corrosive?

A

It corrodes, wears away or destroys things

42
Q

What ions does salt water contain?

A

Sodium, chloride, hydrogen and hydroxide ions

43
Q

What is produced at the anode and cathode from the electrolysis of salt water?

A

Chlorine and hydrogen gas

44
Q

What happens to the ions left over from the electrolysis of salt water?

A

They form a solution of sodium hydroxide

45
Q

Why is platinum wire used for flame tests?

A

It is inert

46
Q

What can affect what happens during electrolysis?

A
  • type of electrode used
  • concentration of the solution
  • distance between the electrodes
  • the current
47
Q

Why does increasing current increase the amount of product produced during electrolysis?

A

It increases the amount of electrons available at the electrodes for oxidation and reduction

48
Q

Why must copper used for the production of wires be very pure?

A

Impurities increase resistance so the wire can get hot which can be dangerous

49
Q

What process is used to extract copper from its ore?

50
Q

What is smelting?

A

The extraction of ores by heating them with carbon

51
Q

How is copper purified on an industrial scale after its extraction by smelting?

A

By electrolysis

52
Q

What does it mean when a product is impure?

A

It contains a mixture of other elements and compounds

53
Q

What does it mean when a product is refined?

A

It’s purity is increased

54
Q

What are the electrodes used during the electrolysis of copper ore made from?

A
  • the anode is the impure copper

- the cathode is a thin sheet of pure copper

55
Q

What electrolyte is used in the electrolysis of copper ore?

A

Copper sulphate solution

56
Q

How many electrons do copper atoms in the anode lose during the electrolysis of copper ore?

57
Q

What are insoluble impurities from the anode during the electrolysis of copper ore called?

58
Q

Why is anode sludge from the electrolysis of copper ore collected?

A

It could contain valuable metallic elements

59
Q

What happens to dissolved copper ions from the anode during the electrolysis of copper ore?

A

They migrate towards the cathode where they are deposited as pure copper

60
Q

Why does the cathode increase in mass as the anode decreases in mass during the electrolysis of copper ore?

A

Because for every copper atom that leaves the anode, one is deposited at the cathode

61
Q

What happens when you electroplate something?

A

A thin layer of metal is deposited on the surface of another

62
Q

What process is used to electroplate objects?

A

Electrolysis

63
Q

What electrode is the object to be plated when you’re electroplating something?

A

The cathode

64
Q

What electrode is made of pure metal when you’re electroplating something?

65
Q

What ions must the electrolyte contain when you’re electroplating something?

A

Ions from the plating metal (the anode)

66
Q

What electrode does reduction occur at?

A

The cathode

67
Q

What electrode does oxidation occur at?

68
Q

How do you increase the thickness of the layer of metal when electroplating?

A
  • increasing the current

- carrying out electrolysis for longer

69
Q

Why would an object be electroplated?

A
  • to give an attractive appearance
  • it’s cheaper than making the object out of pure metal
  • to improve resistance to corrosion
70
Q

How does electroplating a metal improve its resistance to corrosion?

A

It prevents the plated metal from making contact with air

71
Q

What is Galvanised steel?

A

Steel coated with zinc

72
Q

What is rusting?

A

The corrosion of iron

73
Q

Why does zinc protect iron in galvanised steel even when the coating is scratched?

A

Zinc is more reactive

74
Q

What are the uses of electroplating with silver?

A
  • cutlery

- sports trophies

75
Q

What are the uses of electroplating with gold?

76
Q

What are the uses of electroplating with chromium?

A
  • wheel rims

- jewellery

77
Q

What are the uses of electroplating with tin?

A

Steel food cans

78
Q

What are the uses of electroplating with zinc?

A
  • iron nails

- steel railings

Chemistry extension edexcel (5 decks)

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