C3.3 Electrolytic processes Flashcards Preview

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Flashcards in C3.3 Electrolytic processes Deck (82)
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1

How do you break the bonds in an ionic solid?

By melting it or dissolving it in water

2

What are electrolytes?

Ionic substances that conduct electricity when molten or in aqueous solution

3

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

Because then the ions are able to move freely

4

What is electrolysis?

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

5

What electrical supply does electrolysis use?

DC (direct current)

6

What things are necessary to carry out electrolysis?

-a DC electricity supply
-two electrodes
-an electrolyte

7

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

Electrostatic forces of attraction

8

What charge does a cathode have?

Negative

9

What charge does an anode have?

Positive

10

What charge does a cation have?

Positive

11

What charge does an anion have?

Negative

12

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

Orange-brown

13

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

Blue

14

What are electrodes made out of?

Metal or carbon

15

What happens to ions at the cathode?

Electrons from the negative cathode are transferred to the positive ions

16

What happens to ions at the anode?

The negative ions lose electrons to the positively charged anode

17

What is reduction?

When positive ions gain electrons

18

What is oxidation?

The loss of electrons by a negative ion

19

Why do chemical changes occur at the electrodes?

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

20

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

Sodium ions

21

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

Chloride ions

22

What is produced from the electrolysis of NaCl?

Sodium metal and chlorine gas

23

What are the uses of sodium?

In street lamps and as a coolant in nuclear reactions

24

How is sodium used in street lamps?

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

25

How is sodium used as a coolant in nuclear reactions?

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

26

What does a half-equation for electrolysis show?

The change at just one of the electrodes

27

Why is hydrogen a clean fuel?

-it doesn't produce any of the pollutants that fossil fuels produce
-it doesn't produce carbon dioxide

28

What does it mean when a material is inert?

It won't react

29

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

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

30

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

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

31

What does Hoffman's voltameter do?

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

32

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

They become discharged as atoms or molecules at the electrodes

33

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

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

During the electrolysis of water, where is hydrogen produced?

At the cathode

35

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

It needs to dissociate into ions

35

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

They break

35

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

Bromine

35

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

A gas

35

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

A brown vapour

36

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

Molten (liquid)

37

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

Lead metal

38

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

Hydroxide ions lose electrons more readily than sulphate ions

39

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

Hydrogen gas

40

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

Water and oxygen

41

What does it mean when a material is corrosive?

It corrodes, wears away or destroys things

42

What ions does salt water contain?

Sodium, chloride, hydrogen and hydroxide ions

43

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

Chlorine and hydrogen gas

44

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

They form a solution of sodium hydroxide

45

Why is platinum wire used for flame tests?

It is inert

46

What can affect what happens during electrolysis?

-type of electrode used
-concentration of the solution
-distance between the electrodes
-the current

47

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

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

48

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

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

49

What process is used to extract copper from its ore?

Smelting

50

What is smelting?

The extraction of ores by heating them with carbon

51

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

By electrolysis

52

What does it mean when a product is impure?

It contains a mixture of other elements and compounds

53

What does it mean when a product is refined?

It's purity is increased

54

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

-the anode is the impure copper
-the cathode is a thin sheet of pure copper

55

What electrolyte is used in the electrolysis of copper ore?

Copper sulphate solution

56

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

Two

57

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

Sludge

58

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

It could contain valuable metallic elements

59

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

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

60

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

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

61

What happens when you electroplate something?

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

62

What process is used to electroplate objects?

Electrolysis

63

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

The cathode

64

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

The anode

65

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

Ions from the plating metal (the anode)

66

What electrode does reduction occur at?

The cathode

67

What electrode does oxidation occur at?

The anode

68

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

-increasing the current
-carrying out electrolysis for longer

69

Why would an object be electroplated?

-to give an attractive appearance
-it's cheaper than making the object out of pure metal
-to improve resistance to corrosion

70

How does electroplating a metal improve its resistance to corrosion?

It prevents the plated metal from making contact with air

71

What is Galvanised steel?

Steel coated with zinc

72

What is rusting?

The corrosion of iron

73

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

Zinc is more reactive

74

What are the uses of electroplating with silver?

-cutlery
-sports trophies

75

What are the uses of electroplating with gold?

Jewellery

76

What are the uses of electroplating with chromium?

-wheel rims
-jewellery

77

What are the uses of electroplating with tin?

Steel food cans

78

What are the uses of electroplating with zinc?

-iron nails
-steel railings