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Chemistry > C6 Electrolysis Past Papers > Flashcards

C6 Electrolysis Past Papers Flashcards

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1
Q

Products at anode and cathode of electrolysing potassium iodide solution

A

Hydrogen at cathode

Oxygen at anode

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2
Q

Why is oxygen formed at the anode of electrolysis potassium iodide

A

Hydroxide ions are more easily oxidized than iodide ions as they have a lower oxidation potential

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3
Q

Why is hydrogen formed at the cathode of electrolysis potassium iodide

A

If metal element formed during electrolysis is more reactive than hydrogen, then hydrogen will be produced at the cathode

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4
Q

What happens if you place a growing splint in the tube of the gas

A

Will burn more brightly as oxygen is supporter of combustion

Relights

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5
Q

How to test the gas to show it’s hydrogen

A

Hydrogen ignites in air so if hydrogen is present in a test tube

A lighted splint held near its mouth ignites with a squeaky pop

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6
Q

why is hydrogen not magnesium produced at anode during electrolysis

A

It is less reactive than magnesium

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7
Q

Give 1 reason why metal spoons are sometimes silver plated

A

Chemical resistance

Expensive appearnce

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8
Q

The student found that the metal spoon eroded and a thin layer of copper formed on the pure silver electrode

Suggest two changes that the student must make to his apparatus to be able to silver plate the metal spoon. Give a reason for each change.

A

Solution must be silver nitrate or contain silver ions or silver will not be deposited

Spoon must be the cathode as silver ions have positive charge

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9
Q

Why is it difficult to electroplate plastic spoons

A

Plastic is not a conductor of electricity

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10
Q

Why can aluminium not be extracted by heating aluminium oxide with carbon

A

Aluminium is more reactive than carbon

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11
Q

Explain why aluminium forms at the negative electrode during electrolysis

A

Has positive ions that are attracted to the negative electrode where they can gain electrons and be reduced

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12
Q

Explain how carbon dioxide forms at the positive electrodes during electrolysis.

A

Molten aluminium sinks to the bottom of the cell, where it is tapped off.

This oxygen reacts with the carbon of the positive electrodes, forming carbon dioxide

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13
Q

How could the students separate silver from silver nitrate solution

A

Filtration

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14
Q

Determine mass of silver produced after 12 min

A

0.14

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15
Q

Observation at cathode of copper sulfate

A

Copper plating

Pink, red, orange

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16
Q

Observation at cathode sodium chloride

A

Bubbles and fizzing

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17
Q

A teacher demonstrates the electrolysis of molten lead bromide

The products at the electrodes are lead and bromine

Why should the teacher do the demonstration in a fume cupboard

A

Toxic/poisonous fumes

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18
Q

Electrolysis and chemical cells both involve chemical reactions and electricity

Explain the difference between the processes in electrolysis and in a chemical cell

A

Voltage for electricity

Current for electricity

19
Q

Balance the equation

___Br- ———> _________ + ________

A

2Br- ———> Br2 + 2e-

20
Q

What is formed at anode in copper nitrate electrolysis

A

Oxygen

21
Q

Why is oxygen formed at anode in copper nitrate electrolysis

A

No halogen present

22
Q

Some of the copper produced did not stick to the negative electrode but fell to the bottom of the beaker

Suggest how the students could find the total mass of copper produced

A

Filter mixture

Wash and dry the copper / residue

Weigh copper collected

Add to the increase in mass of the electrode

23
Q

A student correctly concluded that the total mass of copper produced is directly proportional both to the time and to the current

How do the results in Figure 2 support the conclusion that the total mass of copper produced is directly proportional to the time?

A

When time doubles, mass doubles

24
Q

How do the results in Figure 2 support the conclusion that the total mass of copper produced is directly proportional to the current

A

When current doubles, mass doubles

25
Q

Why blue colour of copper nitrate solution fades during electrolysis

A

Solution becomes less concentrated

26
Q

Determine the number of atoms of copper produced when copper nitrate solution is electrolysed for 20 minutes at a current of 0.6 A

A

-3
0.24 ➗ 63.5 = 3.78 x 10 or 0.00378
23 21
0.00378 x 6.02 x 10 = 2.28 x 10

27
Q

Observation if metal produced at negative electrode

A

Solid produced

28
Q

Observation if gas produced at positive electrode

A

Bubbles

29
Q

Which salt solution in table above does not match the student’s hypothesis

Give one reason why

A

Potassium nitrate

Hydrogen is not a metal

30
Q

2 reasons why graphite is used for electrodes

A

Conducts electricity

Inert

31
Q

The purple crystal dissolved in the electrolyte solution

What happens to the purple coloured ions

A

Ions move towards the positive electrode

Opposite charges attract

32
Q

Why aluminium has high melting point

A

Strong metallic bonds

33
Q

Alloy

A

Mixture of metals

34
Q

Bauxite contains between 15% and 25% aluminium

Aluminium oxide always contains 53% aluminium

How does this show that bauxite is a mixture and not a compound

A

Bauxite contains variable percentage of aluminium

35
Q

Suggest two possible problems with storing the waste material in lakes of mud

A

Danger from dam bursting

Damage to habitats

36
Q

How do you know when oxygen is produced at anode

A

Oxygen is produced unless halide

As halide ions have single negative charge

37
Q

What is positive electrode made of in molten aluminium oxide

A

Carbon

38
Q

Why is anode usually made of carbon

A

Good conductor

Cheap

39
Q

A sample of bauxite contains 25% aluminium

Calculate maximum mass of aluminium that can be extracted from 300000 kg of the sample of bauxite

A

25
______ x 300,000

100

40
Q

Why colour changed at positive electrode copper chromate solution

A

2-
CrO4 Chromate ions moved to positive electrode as opposite charges attract

41
Q

Name the substance in the solution that provides the hydroxide ions

A

Water

42
Q

How the solid forms at negative electrode

A

Copper ions gain 2 electrons to form copper

43
Q

Explain why a mixture is used as the electrolyte instead of using only aluminium oxide

A

Mixture has lower melting point so less energy needed

44
Q

What happens at the negative electrode during the production of aluminium

A

Aluminium ions gain electrons

Chemistry (10 decks)

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