C2.7

Question 1

What is electrolysis?

Answer 1

The breaking down of an ionic compound, making elements, using electricity

Question 2

What is reduction?

Answer 2

When positively charged ions gain electrons at the negative electrode

Question 3

What is oxidation?

Answer 3

When negatively charged ions lose electrons at the positive electrode

Question 4

What do ions of less reactive elements do?

Answer 4

Accept electrons more readily

Question 5

What is bauxite?

Answer 5

Aluminium ore

Question 6

What is a redox reaction?

Answer 6

A chemical reaction in which both reduction and oxidation happen

Question 7

Why must aluminium oxide be molten for electrolysis?

Answer 7

Because when it is molten the ions are free to move

Question 8

What are the products of the electrolysis of sodium chloride solution (brine) used for?

Answer 8

~ Chlorine is used to kill bacteria in swimming pools, as disinfectant, and to produce plastics
~ Hydrogen is used to make ammonia and margarine
~ Sodium hydroxide is used to make detergents

Question 9

Why is electrolysis used to electroplate objects?

Answer 9

~ Protects them from corrosion

~ Improves their appearance

Question 10

When is electrolysis used to purify metals?

Answer 10

After they’ve been extracted from their ore

Question 11

What needs to happen for copper to be purified?

Answer 11

~ The positive electrode needs to be made of impure copper
~ The negative electrode needs to be made of pure copper
~ The solution must contain copper ions

Question 12

What electrode will the copper ions move to?

Answer 12

The negative electrode to gain electrons and form copper atoms which stick to the pure copper electrode and can be extracted

Question 13

Why is cryolite used in aluminium extraction?

Answer 13

Because it lowers the melting point and allows electrolysis to be carried out at a lower temperature

Question 14

Why do the electrodes need to be replaced in aluminium extraction?

Answer 14

Because as the oxygen reacts with carbon electrode, the electrode slowly disappears and needs to be replaced

Question 15

Why do ionic compounds need to be molten or in solution to do electrolysis?

Answer 15

Because their ions need to be free to move to carry the electricity

Question 16

In the electrolysis of sodium chloride, why is hydrogen produced at the negative electrode and not the sodium?

Answer 16

Hydrogen is less reactive than sodium

Question 17

What are the products of the electrolysis of sodium chloride solution?

Answer 17

~ Chlorine gas at the positive electrode
~ Hydrogen gas at the negative electrode
~ Sodium hydroxide

Question 18

Why is aluminium a useful metal?

Answer 18

~ Very strong

~ Very light

Question 19

What does aluminium ore (bauxite) contain?

Answer 19

~ Aluminium ore

~ Impurities

Question 20

Why can’t aluminium oxide be broken down by heating it with carbon?

Answer 20

Because aluminium is more reactive than carbon so it will hold on to the oxygen

Question 21

What is the problem with melting aluminium oxide?

Answer 21

~ Aluminium melts at about 2000 degrees
~ Costs lots
~ Uses lots of energy

Question 22

What is an electrolyte?

Answer 22

A substance that electrolysis is carried out on

Question 23

What is done before lead bromide is broken down via electrolysis?

Answer 23

It’s heated

Question 24

If the electrolyte contains a mixture of ions, the products formed depend on what?

Answer 24

The reactivity of the elements involved

Question 25

How can aluminium be collected when extracting it?

Answer 25

It sinks to the bottom of the container because it’s more dense than the aluminium oxide and cryolite mixture

Question 26

Why is carbon dioxide produced from the electrolysis of aluminium oxide and cryolite?

Answer 26

~ Oxygen forms at the positive electrode

~ The positive electrode is made of carbon which reacts with the oxygen, producing carbon dioxide

Question 27

What is a test for chlorine?

Answer 27

It bleaches damp litmus paper (removes the colour)