C6

Question 1

electrolysis

Answer 1

electrolysis breaks down a substance using electricity

Question 2

Ionic compounds

Answer 2

Ionic compounds can only be electrolysed when they’re molten or dissolved in water. This is because their ions are then free to move and carry their charge to the electrodes.

Question 3

ions

Answer 3

In electrolysis, positive ions move to the cathode, while negative ions move to the anode.

Question 4

electrolysis of solutions

Answer 4

• many ionic substances have very high melting points so its takes lot of energy to melt them and free the ions to move to electrodes in electrolysis
• some ionic substances dissolve in water when this happens and become free to move around

Question 5

changes at the electrodes

Answer 5

• in electrolysis the ions move towards the oppositely charged electrodes
• at the cathode positive ions gain electrons so are reduces
• at the anode negative ions lose their extra electrons, so are oxidised

Question 6

electrolysis in solutions

Answer 6

• the less reactive element (hydrogen or metal) is produced at the cathode
• at the anode you get oxygen gas given off from discharged hydroxide ions or a halogen produced if the electrolyte is a halide solution

Question 7

aluminium

Answer 7

aluminium oxide from the ore bauxite is electrolysed in the extraction of aluminium metal

Question 8

electrolysis of aluminium

Answer 8

• aluminium oxide is mixed with molten cryolite to lower its melting point reducing energy needed to extract aluminium
• aluminium forms at the cathode and oxygen forms at the anode
• carbon anodes are replaced regularly as they gradually burn away as oxygen reacts with anodes, forming CO2

Question 9

electrolysis of aqueous solutions

Answer 9

• when electrolyse sodium chloride solution you get chlorine gas, hydrogen gas given off at electrodes and sodium hydroxide solution left in solution
• hydrogen produced at the cathode
• chlorine produced at anode