extra questions - C6

Question 1

Why should a teacher demonstrate the electrolysis of molten lead bromide in a fume cupboard?

Answer 1

Toxic/poisonous fumes

Question 2

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

Answer 2

• electrolysis uses electricity to produce a chemical
• cells use chemical reactions to produce electricity

Question 3

During electrolysis, 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 the copper
• weigh the copper collected
• add to the increase in mass of the electrode

Question 4

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

Answer 4

The copper ions are discharged from the solution

Question 5

Why do positive ions move towards the negative electrode

Answer 5

The electrode attracts ions of the opposite charge

Question 6

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

Answer 6

• danger of dam bursting
• visual pollution

Question 7

A student investigated the electrolysis of copper chromate solution. Explain why the colour changed at the positive electrode

Answer 7

• chromate ions moved to the positive electrode
• because opposite charges attract

Question 8

Does oxidation happen at the anode or cathode

Answer 8

anode

Question 9

does reduction happen at the anode or cathode

Answer 9

cathode

Question 10

half equation for the discharge of bromide ions

Answer 10

2Br- -> Br2 + 2e-

Question 11

what is the pH of sodium hydroxide solution

Answer 11

13

Question 12

Describe what happens at the negative electrode of molten zinc chloride

Answer 12

because zinc ions gain electrons

2 (electrons)

zinc is formed

Question 13

Explain, in terms of bonding, why pure water does not conduct electricity.

Answer 13

because (pure) water is covalent

therefore (pure) water has no free ions

Question 14

Why do alkaline batteries eventually stop working?

Answer 14

a reactant is used up

Question 15

 
Why can alkaline batteries not be recharged?

Answer 15

the reaction is not reversible

Question 16

Explain why magnesium chloride must be molten or dissolved in water to be electrolysed.

Answer 16

because ions can move, carry charge