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chemistry (paper one) > electrolysis (topic 4) > Flashcards

electrolysis (topic 4) Flashcards

1
Q

suggest one reason why spoons are electroplated (metal spoons coated with silver)

A

improve appearance

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2
Q

at the cathode (negative electrode) is it the most or least reactive of the two elements that will be produced

A

least reactive

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3
Q

what is the type of bond in a molecule of hydrogen chloride

A

covalent

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4
Q
A
  • hydrogen chloride has a low boiling point
  • hydrogen chloride is made of simple molecules
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5
Q

name a gas produced at the negative electrode

A

hydrogen

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6
Q

hydrogen is only produced at the cathode if the metal

A

if the metal is more reactive than hydrogen

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7
Q

name a gas produced at the positive electrode

A

oxygen

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8
Q

explain why aluminium ions move towards the negative electrode (2)

A
  • aluminium ions are positive
  • so are attracted (to the negative electrode)
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9
Q
A

c

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10
Q
A

atoms

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11
Q
A
  • insoluble
  • precipitation
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12
Q

name the product formed at the postitive electrode

A

chlorine

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13
Q
A

cryolite

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14
Q

what is used as a solvent for aluminium oxide

A

molten cryolite

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15
Q

explain why oxide ions (O2−) move to the positive electrode (2)

A
  • oxide ions are negative
  • so are attracted to the positive electrode
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16
Q
A

reacts with oxygen

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17
Q

(2)

A
  • alloy atoms are not in layers
  • so alloy layers cannot slide
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18
Q
A
  • it is an opinion
  • not enough reliable evidence
  • may be other factors involved
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19
Q

a is
b is
c is

A

a is chlorine gas
b is hydrogen gas
c is sodium hydroxide solution

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20
Q
A
  • the solution may not have been properly stirred
  • the electrodes may have been a larger distance apart
  • the drop of sodium chloride may have been a smaller volume
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21
Q

explain, in terms of bonding, why pure water does not conduct electricity (2)

A
  • pure water is covalent / molecular (simple) or contains molecules
  • therefore has no free electrons
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22
Q

explain why sodium chloride solution conducts electricity (2)

A
  • because there are ions in sodium chloride
  • which can move or carry the current / charge
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23
Q
A
  • copper / ores are running out / harder to find
  • there are very small amounts of high-grade copper ores left
  • copper metal is in demand
  • copper is expensive
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24
Q
A
  • large amounts
  • waste rock takes up a lot of space
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25
Q

the reaction in the furnace could cause environmental pollution, explain how

A
  • (copper sulfide reacts with oxygen to) produce sulfur dioxide
  • that causes acid rain
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26
Q

the extraction of pure copper is expensive, give one reason why

A
  • large amounts of fuels / energy used (for the furnace and electrolysis)
  • (the extraction has) many steps / stages / processes
  • large amounts of ore / material have to be mined
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27
Q

pure copper is produced by electrolysis of copper sulfate solution, which electrode do the copper ions move towards, give a reason for your answer

A
  • the negative electrode / cathode
  • because copper ions / Cu^2+ are positively charged
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28
Q

what is used in phytomining to remove copper compounds from the land

A

plants

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29
Q

solution X is alkaline, which ion makes solution X alkaline

A
  • hydroxide / OH^–
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30
Q
A
  • hydrogen / H+
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31
Q

(1)

A

low percentage / very little of metal (in the ore)

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32
Q
A

has melting point lower than 950°C

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33
Q

(2)

A
  • electrode made of carbon
  • oxygen reacts with electrode
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34
Q

suggest two reasons why we should recycle aluminium drinks cans

A
  • saves resources / non-renewable
  • landfill problem
  • saves energy
  • less carbon dioxide / carbon emissions
  • less quarrying / mining
35
Q

explain, in terms of ions, why sodium chloride solution conducts electricity (1)

A
  • the ions can move / are free
  • the ions carry the charge / current
36
Q
A

13

37
Q

suggest two possible causes of this anomalous result

A
  • gas escapes
  • weighing error
  • error in measuring (volume / amount) of hydrogen
  • error in measuring (volume / amount) of water
  • incorrect concentration
  • timing error
  • change in voltage / current
  • change in temperature
  • recording / plotting error
38
Q

(4)

A
  • chlorine gas is released at the positive electrode
  • chloride ions are negative
  • copper collects at the negative electrode
  • copper ions are positive
39
Q

explain why copper metal is formed when electricity is passed through dilute copper chloride, but hydrogen gas is formed when electricity is passed through dilute sodium chloride (2)

A
  • copper is less reactive than hydrogen
  • sodium is more reactive than hydrogen
40
Q
A

copper sulfate

41
Q

(2)

A
  • copper sulfate is safer to use as copper chloride produces chlorine which is a toxic gas but copper sulfate does not
  • zinc bromide and sulfuric acid cannot be used as they do not have copper ions
42
Q
A
43
Q

(4)

A
  • solution must be silver nitrate or contain silver ions
  • otherwise copper will be deposited or silver will not be deposited
  • spoon must be the negative electrode
  • because silver ions have a positive charge
44
Q

what is meant by electrolysis (2)

A
  • breakdown of an ionic compound into elements
  • using electricity
45
Q

give two observations which would only be seen in experiment 2 (2)

A
  • bulb lights up
  • chlorine is given off
46
Q

explain why no changes would be seen in experiment 1 (2)

A
  • ions in a solid ionic compound
  • are not free to move
47
Q

electrolysis and chemical cells both involve chemical reactions and electricity, explain the difference between the processes in electrolysis and in a chemical cell (2)

A
  • electrolysis uses electricity to produce a chemical reaction (or electrolysis uses electricity to decompose a compound)
  • chemical cells use a chemical reaction to produce electricity
48
Q
A

hydrogen

49
Q

explain why chloride ions move towards the positive electrode (2)

A
  • chloride ions are negative
  • negative ions move to positive electrode
50
Q

why is the formation of chlorine at this electrode said to be an oxidation reaction (1)

A

there is a loss of electrons

51
Q

write the ionic equations that represent the reactions that take place at each of the electrodes

A
52
Q

name the important alkali which is left in the solution

A

sodium hydroxide

53
Q

describe and explain how electrolysis is used to make pure copper from a lump of impure copper (6)

A

electrodes:
- impure copper is anode
- pure copper is cathode
electrolyte:
- copper sulfate solution
process at the anode:
- copper loses electrons
- copper forms positive ions and goes into solution
- Cu ➔ Cu2+ + 2e–
process at the cathode:
- copper gains electrons
- copper is deposited/collected
- Cu2+ + 2e– ➔ Cu at the negative electrode
what happens to the impurities:
- sludge / impurities collect at the bottom
- because the impurities are not attracted to electrode

54
Q
A

to lower the melting point of the mixture

55
Q
A
  • oxygen
  • carbon
  • carbon dioxide
56
Q

write the balanced half-equation for the process at the positive electrode

A
57
Q

explain why the aluminium ions move to the negative electrode (2)

A
  • aluminium ions are positive
  • so are attracted to the negative electrode
58
Q
A

reduction

59
Q

(2)

A
  • sometimes hydrogen is produced
  • because the metal is more reactive than hydrogen
60
Q

draw a labelled diagram of the apparatus he could use

A
61
Q

give the independent variable in the experiment

A

salt solutions with different metal ions

62
Q

describe what the student would see at the negative electrode if his hypothesis was true (1)

A

solid deposit on the negative electrode

63
Q

(2)

A
  • solid zinc chloride does not conduct electricity
  • because ions cannot move in the solid
64
Q

give two reasons why graphite is used for the electrodes (2)

A
  • graphite conducts electricity
  • graphite is inert
65
Q

zinc ions move towards the negative electrode where they gain electrons to produce zinc, explain why zinc ions move towards the negative electrode (2)

A
  • zinc ions are positive
  • opposite charges attract
66
Q
A

reduction

67
Q

what does ‘electrolyte’ mean (2)

A
  • substance that can be broken down into elements
  • by electric current
  • ions are free to move e.g. when molten or in solution
68
Q

why do copper ions go to the negative electrode (1)

A

copper ions have a positive charge

69
Q

name the gas given off at the positive electrode and state how a sample of gas can be collected (3)

A
  • oxygen
  • tube over electrode
  • full of CuSO4 (aq) / water
70
Q

suggest why the blue colour of copper sulphate becomes paler during the investigation (1)

A

Cu2+ ions have been removed

71
Q

suggest two reasons why copper should not be disposed of in landfill sites (2)

A
  • copper ores are limited
  • copper can be recycled
  • copper can be reused
  • copper is expensive
  • landfill sites are filling up
  • copper compounds are toxic
72
Q

write the formulae of the ions present in:
- an aqueous solution of copper sulfate
- an aqueous solution of sulfuric acid

A
73
Q

(2)

A
  • oxidation
  • electrons lost
74
Q

write a balanced ionic equation for the reaction at the cathode

A
75
Q

what happens to the concentration of the sulphuric acid as the electricity is passed through it, explain your answer (3)

A
76
Q

predict the products made at the electrodes when sodium sulfate solution is electrolysed

A
  • anode:
  • oxygen
  • roduct at the cathode:
  • hydrogen
77
Q

the student was surprised that the product made at the cathode is a gas, explain why the product at the cathode is a gas (sodium sulfate solution is electrolysed, anode: oxygen, cathode: hydrogen)

A

hydrogen is less reactive than sodium

78
Q

explain why aluminium is extracted using electrolysis and not by reduction with carbon (2)

A
  • aluminium is more reactive than carbon
  • so carbon cannot displace aluminium (or so carbon cannot reduce aluminium oxide)
79
Q
A

aluminium ions gain electrons

80
Q

explain why the positive electrode must be continually replaced (3)

A
  • the electrode reacts with oxygen
  • the electrode is graphite
  • so carbon dioxide is produced
81
Q

complete the balanced half-equation for the process that occurs at the positive electrode (electrolysis of aluminium)

A
82
Q
A
83
Q
A

chemistry (paper one) (24 decks)

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