C6(electrolysis)

Question 1

Electrolyte

Answer 1

During electrolysis, an electric current is passed through an electrolyte(a molten or dissolved ionic compound). The ions move towards the electrodes, where they react, and the compound decomposes.

Question 2

Negative electrode

Answer 2

Cathode

Question 3

Positive electrode

Answer 3

Anode

Question 4

What happens at the cathode?

Answer 4

The positive ions in the electrolyte will move towards the cathode and gain electrons(they are reduced).

Question 5

What happens at the anode?

Answer 5

The negative ions in the electrolyte will move towards the anode and lose electrons(they are oxidised).

Question 6

What happens as ions travel to the electrodes?

Answer 6

This creates a flow of charge through the electrolyte. As ions gain or lose electrons, they form the uncharged element and are discharged from the electrolyte.

Question 7

Why can’t an ionic solid be electrolysed?

Answer 7

Because the ions are in fixed positions and can’t move

Question 8

Can molten ionic compounds be electrolysed?

Answer 8

Molten ionic compounds can be electrolysed, because the ions can move freely and conduct electricity.

Question 9

What happens to molten ionic liquids?

Answer 9

Molten ionic liquids are always broken up into their elements. Positive metal ions are reduced to the element at the cathode, while negative non-metal ions are oxidised to the element at the anode.

Question 10

Electrolysis of aluminium oxide

Answer 10

Aluminium oxide: aluminium + oxygen
2Al2O3(l): 4Al(l)+3O2(g)

Question 11

Electrolysis of aluminium from aluminium oxide

Answer 11

1) Aluminium is extracted from the ore bauxite by electrolysis. Bauxite contains aluminium oxide.
2) Aluminium oxide hae a very high melting temperature, so it’s mixed with cryolite to lower the melting point.
3)The molten mixtiure contains free ions - so it’ll conduct electricity.
4) The positive Al3+ ions are attracted to the negative electrode where they each pick up three electrons and turn into neutral aluminium atoms. These then sink to the bottom of the electrolysis tank.
5) The negative O2- ions are then attracted to the positive electrode where they each lose two electrons. The neutral oxygen atoms combine to form O2 molecules.

Question 12

What is the anode made of?

Answer 12

Carbon - needs to be replaced regularly as it reacts with oxygen to produce carbon dioxide

Question 13

Discharging ions from water(at the cathode)

Answer 13

At the cathode, if H+ ions and metal ions are present, hydrogen gas will be produced if the metal ions form an elemental metal that is more reactive than hydrogen(e.g. sodium ions). If the metal ions form an elemental metal less reactive than hydrogen(e.g. copper ions), a solid layer of the pure metal will be produced instead.

Question 14

Discharging ions from water(at the anode)

Answer 14

At the anode, if OH- and halide ions(Cl-,Br-,I-) are present, molecules of chlorine, bromine, or iodine will be formed. If no halide ions are present, then the OH- ions are discharged and oxygen will be formed.