C6 - Electrolysis

Question 1

define electrolysis

Answer 1

use of an electrical current to break down compounds containing ions

Question 2

what is the substance being broken down called?

Answer 2

electrolyte

Question 3

what are the electrodes made from?

Answer 3

substances that conduct electricity.

Question 4

during electrolysis, what moves to the anode (positive electrode)?

Answer 4

negatively charged ions

Question 5

during electrolysis, what moves to the cathode (negative electrode)

Answer 5

positvely charged ions

Question 6

for the electrolysis of molten ionic compounds, what must the electrodes be and why?

Answer 6

the electrodes must be inert so that they do not react with the electrolyte or the products.

Question 7

when can ionic substances ONLY conduct electricity?

Answer 7

when they are molten or dissolved in water

Question 8

when does reduction occur?

Answer 8

when positively charged ions gain electrons at the negative electrode

Question 9

when does oxidation occur?

Answer 9

when negatively charged ions lose electrons at the positive electrode

Question 10

what happens in a redox reaction?

Answer 10

both reduction and oxidation occur.

Question 11

To extract metals from their ores using electrolysis, what must they be?

Answer 11

more reactive than carbon

Question 12

why is electrolysis an expensive process?

Answer 12

as it requires a lot of heat and electrical energy

Question 13

how is aluminium obtained?

Answer 13

by the electrolysis of aluminium oxide that has been mixed with cryolite

Question 14

what does cryolite do?

Answer 14

lowers the melting point of aluminium oxide. less energy needed

Question 15

where does aluminium form?

Answer 15

negative electrode

Question 16

where does oxygen gas form?

Answer 16

at the positive carbon electrode and reacts with the carbon forming carbon dioxide

Question 17

what is the positive electrode made of when electrolysis is used to extract a metal?

Answer 17

carbon

Question 18

what do the water molecules break down to form when ionic compounds are dissolved in water to form aqueous solutions?

Answer 18

hydroxide ions (OH-) , hydrogen ions (H+)

Question 19

what is produced at the negative electrode?

Answer 19

hydrogen if the metal is more reactive than hydrogen. metal is produced if metal is less reactive than hydrogen

Question 20

what is produced at the positive electrode?

Answer 20

oxygen is produced unless solution contains halide ions. if halide ions are present, halogen is produced

Question 21

what happens in the electrolysis of sodium chloride solution?

Answer 21

hydrogen is released at negative electrode, chlorine gas released at positive electrode.

Question 22

Investigate what happens when aqueous solutions are electrolysed using inert electrodes. REQUIRED PRACTICAL

Answer 22

Sample method: set up equipment, pass an electric current through aqueous solution. observe products formed at each inert electrode.

Question 23

explain how copper is produced from copper sulfate solution by electrolysis

Answer 23

• copper ions are positive so they are attracted to the inert cathode
• copper ions gain electrons at the intert cathode so they are reduced to form copper atoms

Question 24

Suggest why the colour of the copper(II) sulfate solution fades during the electrolysis.

Answer 24

• copper ions cause the blue colour.

- copper ions are reduced to copper ions so the concentration of copper ions decreased

Question 25

what products do you get when brine is electrolysed?

Answer 25

chlorine gas at anode
hydrogen gas at cathode
sodium hydroxide solution