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AQA Chemistry - GCSE > Electrolysis > Flashcards

Electrolysis Flashcards

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1
Q

Copper (II) chloride solution electrolysis - anode reaction?

A

2Cl– (aq) → Cl2 (g) + 2e–

This is oxidation

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2
Q

Copper (II) chloride solution electrolysis - cathode reaction?

A

Cu2+(aq) + 2e– → Cu(s)

This is reduction

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3
Q

Sodium chloride solution electrolysis - anode reaction?

A

2Cl– → Cl2 (g) + 2e–

This is oxidation

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4
Q

Sodium chloride solution electrolysis - cathode reaction?

A

2H+ (aq) + 2e– → H2 (g)

This is reduction

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5
Q

Sodium sulfate solution electrolysis - anode reaction?

A

O2- (aq) → O2 (g) + 2e–

This is oxidation

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6
Q

Sodium sulfate solution electrolysis - cathode reaction?

A

2H+ (aq) + 2e– → H2 (g)

This is reduction

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7
Q

Water acidified with sulphuric acid electrolysis - anode reaction?

A

2O2- (aq) → O2 (g) + 4e–

This is oxidation

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8
Q

Water acidified with sulphuric acid electrolysis - cathode reaction?

A

2H+ (aq) + 2e– → H2 (g)

This is reduction

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9
Q

Molten lead bromide electrolysis - anode reaction?

A

2Br– (l) → Br2 (g) + 2e–

This is oxidation

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10
Q

Molten lead bromide electrolysis - cathode reaction?

A

Pb2+(l) + 2e– → Pb (l)

This is reduction

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11
Q

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

A

Chlorine gas

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12
Q

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

A
  • Copper metal (deposited on the cathode )
  • It is a brown / pink colour
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13
Q

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

A

Chlorine gas

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14
Q

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

A

Hydrogen gas

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15
Q

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

A

Oxygen gas

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16
Q

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

A

Hydrogen gas

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17
Q

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

A

Oxygen gas

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18
Q

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

A

Hydrogen gas

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19
Q

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

A

Bubbles of bromine gas

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20
Q

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

A

Lead metal

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21
Q

What does PANIC stand for?

A
  • Positive
  • Anode
  • Negative
  • Is
  • Cathode
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22
Q

What does OILRIG stand for?

A
  • Oxidation
  • Is a
  • Loss of Electrons
  • Reduction
  • Is a
  • Gain of Electrons
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23
Q

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

A

The electrolyte

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24
Q
  • What are the anode and cathode called together?
  • What are they usually made of?
A
  • The electrodes
  • They are usually made of carbon / graphite, but are made of copper when purifying copper (electrolysis of copper sulfate solution).
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25
Q

Is the cathode positive or negative?

A

Negative

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26
Q

Is the anode positive or negative?

A

Positive

27
Q

Which Ionic compounds will conduct electricity?

A
  • 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
Q

Will any covalent compounds conduct electricity?

A

Only graphite, since it has free electrons

29
Q

How can we make lead molten?

A

By heating it to melt the lead

30
Q

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

A
  • 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
Q

What is the test for carbon dioxide gas?

A

Turns limewater milky

32
Q

What is the test for oxygen gas?

A

Relights a glowing splint

33
Q

What is the test for hydrogen gas?

A

Squeaky pop test

34
Q

What is the test for chlorine gas?

A

Red litmus turns blue and is then bleached white

35
Q

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

A
  • Positive = Cu2+ and H+
  • Negative = Cl- and OH-
36
Q

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

A
  • Positive = Na+ and H+
  • Negative = Cl- and OH-
37
Q

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

A
  • Positive = Na+ and H+
  • Negative = SO42- and OH-
38
Q

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

A
  • Positive = H+
  • Negative = SO42- and OH-
39
Q

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

A
  • Positive = Pb2+
  • Negative = Br -
40
Q

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

A

Unreactive

41
Q

What does REDOX stand for?

A

RED - uction and OX - idation

42
Q

Which metal is usually extracted from its ores using electrolysis?

A

Aluminium

43
Q

Why is aluminium extracted from its ores using electrolysis?

A

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

44
Q

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

A

It is mixed with molten Cryolite.

45
Q

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

A

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
Q

What is the name of aluminium ore?

A

Bauxite

47
Q

Where do positively charged cations move to during electrolysis?

A

They move towards the oppositely / negatively charged cathode

48
Q

Where do negatively charged anions move to during electrolysis?

A

They move towards the oppositely / positively charged anode

49
Q

What is an electrolyte?

A

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

50
Q

Define electrolysis

A
  • 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
Q

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

A

Copper

52
Q
  • 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)
A

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

53
Q

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

A
  • Iodine at the anode
  • Potassium at the cathode
54
Q
  • 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)
A

Cu2+ +2e- → Cu

55
Q
  • 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)
A
  • 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
Q

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)

A

D) Graphite

57
Q

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

A

A substance that conducts electricity (1)

When molten or in aqueous solution (1)

58
Q

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.

A

Copper is deposited on the cathode

Mass deposited = 1.57 – 1.28

= 0.29g

59
Q

Which two ions does water dissociate into?

A

OH -

and

H+ ions

60
Q

What do bubbles mean in electrolysis?

A

A gas is being produced

61
Q

Define reduction

A
  • Reduction is a gain of electrons
  • Reduction is also a loss of oxygen
62
Q

Define oxidation

A
  • Oxidation is a loss of electrons
  • Oxidation is also a gain of oxygen
63
Q

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

A
  • 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
Q

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

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

AQA Chemistry - GCSE (4 decks)

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