Elements from the Sea

Question 1

What is electrolysis?

Answer 1

The break down of a molten or dissolved ionic substance using electricity

Question 2

What is an electrolyte?

Answer 2

A liquid that conducts electricity that contains free ions which are either the molten or dissolved ionic substance

Question 3

What occurs at each electrode?

Answer 3

+ (anode): negative ions (anions) move there and lose electrons
- (cathode): positive ions (cations) move there and gain electrons

Question 4

What do the electrodes have to be?

Answer 4

They have to be inert so they don’t react or interfere with the electrolysis (e.g. platinum or carbon)

Question 5

What do half equations show?

Answer 5

The movement of electrons during a reaction

Question 6

What occurs at the negative electrode (cathode) when doing electrolysis of aqueous solutions?

Answer 6

1. If the metal is less reactive than hydrogen (e.g. silver or copper), then the metal will form
2. If the metal is more reactive than hydrogen (e.g. all group 1+2 and aluminium) then hydrogen gas will be formed

Question 7

What occurs at the positive electrode (anode) when doing electrolysis of aqueous solutions?

Answer 7

1. If the solution doesn’t contain a halide. oxygen will be formed
   2.If the solution is concentrated and a halide, the halogen will be formed
2. If the solution contains a halide but is dilute, oxygen will be formed.
3. If you use metal electrodes (apart from platinum), metal ions can also be formed

Question 8

How are halogens produces?

Answer 8

By being extracted by electrolysis of halide solutions where the halogen element is released at the anode. The halide ions lose electrons to the electrode and are oxidised to atoms

Question 9

What is used in the production of chlorine?

Answer 9

Brine- solution of water with high conc. of salts (mainly NaCl)

Question 10

How are bromine and iodine produces?

Answer 10

They can be extracted from brine in a displacement reaction with chlorine. Chlorine is more reactive than both Br and I so when bubbled through brine, the chlorine displaces them. They are both collected, purified and condensed, Br into a liquid, I into a grey solid

Question 11

What are the equations for the production of Br and I?

Answer 11

2Br-(aq) + Cl2 (g) –> Br2 (g) + 2Cl- (aq)
2I- (aq) +Cl2 (g) –> I2 (aq) +2Cl- (aq)