MOCKS

Question 1

why use an instrumental method to measure something?

Answer 1

accurate
sensitive

Question 2

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

Answer 2

electrolysis uses electricity to produce a chemical reaction
a cell uses a chemical reaction to produce electricity

Question 3

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.

Answer 3

Filter the mixture
wash and dry copper
weigh copper
add to increase in mass of electrode

Question 4

Copper nitrate solution is blue.
Suggest why the blue colour of the copper nitrate solution fades during the electrolysis.

Answer 4

copper ions are discharged from the solution

Question 5

Observation if metal produced at the negative electrode

Answer 5

solid produced

Question 6

Observation if gas produced at the positive electrode

Answer 6

bubbles/effervescence

Question 7

Why is graphite used for the electrodes?

Answer 7

graphite conducts electricity
graphite is inert

Question 8

Bauxite contains between 15% and 25% aluminium.
How does this show that bauxite is a mixture and not a compound?

Answer 8

it contains a varying percentage of aluminium

Question 9

Copper chromate contains yellow coloured CrO4^2–ions
Explain why the colour changed at the positive electrode.

Answer 9

chromate ions moves to positive electrode as opposite charges attract

Question 10

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

Answer 10

lowers the melting point
so less energy needed

Question 11

Sodium metal and chlorine gas are produced by the electrolysis of molten sodium chloride.
Explain why sodium chloride solution cannot be used as the electrolyte to produce sodium metal.

Answer 11

hydrogen is produced
as sodium is more reactive than hydrogen

Question 12

Why can solid zinc chloride not be used as an electrolyte?

Answer 12

solid (zinc chloride) does not conduct (electricity)
as ions cannot move in the solid

Question 13

Why can solid zinc chloride not be used as an electrolyte?

Answer 13

solid (zinc chloride) does not conduct (electricity)
as ions cannot move in the solid

Question 14

Why can graphite conduct electricity?

Answer 14

each carbon / atom forms 3 (covalent) bonds
one electron per carbon / atom is delocalised
(so) these electrons carry charge through the graphite

Question 15

How should the solution be heated gently in crystallisation?

Answer 15

using a water bath

Question 16

Why do you warm the acid in crystallisation?

Answer 16

to speed up the reaction

Question 17

Why do you stir the mixture in crystallisation?

Answer 17

to make sure all acid reacts

Question 18

Why do you filter the mixture in crystallisation?

Answer 18

to remove (e.g. magnesium oxide) in excess

Question 19

Explain why an acid can be described as both strong and dilute.

Answer 19

(strong because) completely ionised (in aqueous solution)
(dilute because) small amount of acid per unit volume

Question 20

Explain why the student should use a pipette to measure the dilute sulfuric acid and a burette to measure the sodium hydroxide solution in titration.

Answer 20

pipette measures a fixed volume
burette measures a variable volume

Question 21

What is a weak acid?

Answer 21

produces H+ ions in aqueous solutions
only partially ionised

Question 22

The student repeated the experiment with potassium carbonate.
The limewater did not bubble.
Suggest why there were no bubbles in the limewater.

Answer 22

Potassium carbonate does not decompose to produce carbon
dioxide

Question 23

Advantages of using hydrogen fuel cells over rechargeable cells

Answer 23

no loss of efficiency over time
take less time to refuel (than to recharge rechargeable batteries)
no toxic chemicals to dispose of at the end of cell’s life

Question 24

Suggest factors that could affect the voltage produced in a fuel cell.

Answer 24

concentration of electrolyte
temperature of electrolyte

Question 25

Suggest why trains using hydrogen fuel cells are referred to as ‘steam trains’?

Answer 25

hydrogen is oxidised
water is released as a gas

Question 26

Why can alkaline batteries not be recharged?

Answer 26

the reaction cannot be reversed

Question 27

Why do non-rechargeable cells stop producing electricity?

Answer 27

the reaction stops as reactants are used up