Chemical Changes

Question 1

Electrolyte

Answer 1

Liquid / Solution contain ions which are free to move so can conduct electricity

Question 2

What happens when an ELECTRIC CURRENT is passed through the electrolyte?

Answer 2

Ions moved to the ELECTRODES

Cations (positive ions) move to the CATHODE (negative electrode)

Anions (negative ions) move towards the ANODE (positive electrode)

Ions are discharged at the electrodes to produce ELEMENTS.

This is called electrolysis.

Question 3

What happens when Lead Bromide is Electrolysed?

Answer 3

• Cations (lead) moves towards the cathode
• Anions, (bromine) move towards anode
• They are electrolysed and elements are extracted

Question 4

How can we extract metals from molten compounds?

Answer 4

Electrolysis

Question 5

What are the conditions for which we use electrolysis?

Answer 5

• used if the metal is more reactive than carbon

Question 6

What is an issue with electrolysing aluminium oxide?

Answer 6

• aluminium oxide is INSOLUBLE in water
• and has a HIGH MELTING POINT
• so a lot of energy must be transferred to break it’s strong ionic bonds, which is EXPENSIVE
• to reduce costs powdered aluminium oxide is dissolved in molten cryolite, which melts at lower temperatures
• nevertheless it is still an expensive process

Question 7

Why must the anode be frequently replaced?

Answer 7

• Because the oxygen ions, (anions) react with the CARBON ELECTRODE
• so anode is gradually OXIDISED
• this adds to the cost of extracting aluminium

Question 8

Electrolysis of aqueous solutions -

Answer 8

• at cathode, hydrogen is produced if the metal is MORE REACTIVE than hydrogen
• at anode, oxygen is produced unless the solution contains HALIDE IONS, when the halogen is produced

This happens because in aqueous solutions, water molecules break down producing hydrogen ions and hydroxide ions which are discharged

Question 9

What happens at the cathode?

Answer 9

• cathode (negative electrode)
• attracts cations (positive ions)
• attracts METALS (the positive ions)
• positively charged ions GAIN ELECTRONS
• so REDUCTION occurs

Question 10

What happens at the anode?

Answer 10

• Anode (positive electrode)
• Attracts anions (negative ions)
• Anions are NON-METALS
• Negatively charged ions LOSE ELECTRONS
• So OXIDIATION occurs at ANODE

Question 11

What happens when a metal reacts with oxygen?

Answer 11

• metals oxide

- metal is oxidised

Question 12

How can metals less reactive than carbon be extracted from their oxides?

Answer 12

They can be reduced with carbon

Question 13

What is a redox reaction?

Answer 13

Reactions where oxidation and reduction are both taking place