Electrolysis Flashcards Preview

AQA Chemistry - GCSE > Electrolysis > Flashcards

Flashcards in Electrolysis Deck (64):
1

Copper (II) chloride solution electrolysis - anode reaction?

2Cl (aq) → Cl2 (g) + 2e

This is oxidation

2

Copper (II) chloride solution electrolysis - cathode reaction?

Cu2+(aq) + 2e → Cu(s)

This is reduction

3

Sodium chloride solution electrolysis - anode reaction?

2Cl → Cl2 (g) + 2e

This is oxidation

4

Sodium chloride solution electrolysis - cathode reaction?

2H+ (aq) + 2e → H2 (g)

This is reduction

5

Sodium sulfate solution electrolysis - anode reaction?

O2- (aq) → O2 (g) + 2e

This is oxidation

6

Sodium sulfate solution electrolysis - cathode reaction?

2H+ (aq) + 2e → H2 (g)

This is reduction

7

Water acidified with sulphuric acid electrolysis - anode reaction?

2O2- (aq) → O2 (g) + 4e

This is oxidation

8

Water acidified with sulphuric acid electrolysis - cathode reaction?

2H+ (aq) + 2e → H2 (g)

This is reduction

9

Molten lead bromide electrolysis - anode reaction?

2Br (l) → Br2 (g) + 2e

This is oxidation

10

Molten lead bromide electrolysis - cathode reaction?

Pb2+(l) + 2e → Pb (l)

This is reduction

11

Copper (II) chloride solution electrolysis - what is formed at the anode?

Chlorine gas

12

Copper (II) chloride solution electrolysis - what is formed at the cathode?

  • Copper metal (deposited on the cathode )
  • It is a brown / pink colour

13

Sodium chloride solution electrolysis - what is formed at the anode?

Chlorine gas

14

Sodium chloride solution electrolysis - what is formed at the cathode?

Hydrogen gas

15

Sodium sulfate solution electrolysis - what is formed at the anode?

Oxygen gas

16

Sodium sulfate solution electrolysis - what is formed at the cathode?

Hydrogen gas

17

Water acidified with sulphuric acid electrolysis - what is formed at the anode?

Oxygen gas

18

Water acidified with sulphuric acid electrolysis - what is formed at the cathode?

Hydrogen gas

19

Molten lead bromide electrolysis - what is formed at the anode?

Bubbles of bromine gas

20

Molten lead bromide electrolysis - what is formed at the cathode?

Lead metal

21

What does PANIC stand for?

  • Positive
  • Anode
  • Negative
  • Is
  • Cathode

22

What does OILRIG stand for?

  • Oxidation
  • Is a
  • Loss of Electrons

 

  • Reduction
  • Is a
  • Gain of Electrons

23

What is the name of the liquid in an electrolysis cell?

The electrolyte

24

  • What are the anode and cathode called together?
  • What are they usually made of?

  • The electrodes
  • They are usually made of carbon / graphite, but are made of copper when purifying copper (electrolysis of copper sulfate solution).

25

Is the cathode positive or negative?

Negative

26

Is the anode positive or negative?

Positive

27

Which Ionic compounds will conduct electricity?

  • Only ionic compounds that are molten (heated to melt) or dissolved in solution will conduct electricity.
  • This means that ions can move and transfer the current.

28

Will any covalent compounds conduct electricity?

Only graphite, since it has free electrons

29

How can we make lead molten?

By heating it to melt the lead

30

How do we know if hydrogen or a metal forms at the negative cathode?

  • Hydrogen gas is only produced at the cathode if the metal is more reactive than hydrogen (e.g. sodium with sodium sulphate electrolysis).
  • Copper is less reactive than hydrogen, so is produced at the anode (e.g. with copper (II) chloride electrolysis).

31

What is the test for carbon dioxide gas?

Turns limewater milky

32

What is the test for oxygen gas?

Relights a glowing splint

33

What is the test for hydrogen gas?

Squeaky pop test

34

What is the test for chlorine gas?

Red litmus turns blue and is then bleached white

35

Which ions are involved in the electrolysis of copper (II) chloride solution?

  • Positive = Cu2+ and H+
  • Negative = Cl- and OH-

36

Which ions are involved in the electrolysis of sodium chloride solution?

  • Positive = Na+ and H+
  • Negative = Cl- and OH-

37

Which ions are involved in the electrolysis of sodium sulfate solution?

  • Positive = Na+ and H+
  • Negative = SO42- and OH-

38

Which ions are involved in the electrolysis of water acidified with sulphuric acid?

  • Positive = H+
  • Negative = SO42- and OH-

39

Which ions are involved in the electrolysis of molten lead bromide?

  • Positive = Pb2+
  • Negative = Br -

40

What does inert mean (when talking about the electrodes)?

Unreactive

41

What does REDOX stand for?

RED - uction and OX - idation

42

Which metal is usually extracted from its ores using electrolysis?

Aluminium

43

Why is aluminium extracted from its ores using electrolysis?

Aluminium is too reactive to extract by using carbon to displace it from its ore

44

What is aluminium ore (bauxite) mixed with to reduce the cost of its electrolysis?

It is mixed with molten Cryolite.

45

Give two reasons why cryolite is used in the electrolysis of aluminium oxide.

1) Mixture of cryolite and aluminium oxide has a lower melting point than pure aluminium oxide.

2) This means a lower amount of energy is required to establish effective conditions for electrolysis - more cost effective.

46

What is the name of aluminium ore?

Bauxite

47

Where do positively charged cations move to during electrolysis?

They move towards the oppositely / negatively charged cathode

48

Where do negatively charged anions move to during electrolysis?

They move towards the oppositely / positively charged anode

49

What is an electrolyte?

Electrolytes are ionic compounds in the molten state or dissolved in water

50

Define electrolysis

  • Passing an electric current through electrolytes causes the ions to move to the electrodes.
  • Positively charged ions move to the negative electrode (the cathode) and negatively charged ions move to the positive electrode (the anode).
  • Ions are discharged at the electrodes producing elements.

51

What are the electrodes made of during the purification of copper in the electrolysis of copper sulfate solution?

Copper

52

  • EXAM QUESTION: Zinc can be extracted from its ore by electrolysis or by heating the ore with carbon.
  • Give a reason for the actual method that is used. (1 mark)

Heating with carbon is used since it is cheaper than using electrolysis.

53

EXAM QUESTION: Identify the products formed at the anode and cathode when molten potassium iodide is electrolysed. (2 marks)

  • Iodine at the anode
  • Potassium at the cathode

54

  • EXAM QUESTION: Copper is purified by the electrolysis of copper sulfate solution using an impure copper anode and a pure copper cathode.
  • Write the half-equation for the formation of a copper atom from a copper ion. (2 marks)

Cu2+ +2e- → Cu

55

  • EXAM QUESTION: When a solution of sodium sulfate, Na2SO4, is electrolysed, the products formed at the electrodes are hydrogen and oxygen.
  • Explain the formation of the products at the electrodes. (4 marks)

  • Hydrogen (H) and sodium (Na) ions attracted to the cathode
  • Hydroxide (OH− ) ions and sulfate (SO42− ) ions attracted to the anode
  • Since the ions are attracted to the oppositely charged electrode

2H+ (aq) + 2e → H2 (g)

O2- (aq) → O2 (g) + 2e

56

EXAM QUESTION: Which material is most suitable to make the electrodes for the electrolysis of a dilute acid?

A) zinc

B) sulfur

C) iron

D) graphite         (1 mark)

D) Graphite

57

EXAM QUESTION: State what is meant by the term electrolyte (2 marks)

A substance that conducts electricity (1)

When molten or in aqueous solution (1)

58

EXAM QUESTION: Copper sulfate solution was electrolysed for five minutes using copper electrodes.

Anode mass BEFORE electrolysis = 1.16g

Anode mass AFTER electrolysis = 0.85g

Cathode mass before electrolysis = 1.28g

Cathode mass after electrolysis = 1.57g

Calculate the mass of copper deposited.

Copper is deposited on the cathode

Mass deposited = 1.57 – 1.28

  = 0.29g

59

Which two ions does water dissociate into?

OH -

and

H+ ions

60

What do bubbles mean in electrolysis?

A gas is being produced

61

Define reduction

  • Reduction is a gain of electrons
  • Reduction is also a loss of oxygen

62

Define oxidation

  • Oxidation is a loss of electrons
  • Oxidation is also a gain of oxygen

63

Aluminium manufacture - why must the positive electrode be continually replaced?

  • Oxygen reacts with the carbon in the electrodes, forming carbon dioxide which bubbles off.
  • Carbon is therefore lost from the positive electrodes, so they must be replaced frequently.
  • This adds to the cost of the process

64

What do the molecules of water in an aqueous solution break down into during electrolysis?

  • Hydrogen (H+) ions
  • Hydroxide (OH-) ions