Electrolysis

Question 1

Why don’t covalent compounds conduct electricity?

Answer 1

There are strong covalent bonds holding compounds together so there are no free ions or electrons to move and carry charge.

Question 2

Why do ionic compounds conduct electricity only when molten or in aqueous?

Answer 2

Ionic compounds cannot conduct electricity when solid because there are no free electrons to move and carry charge, and ions are fixed by strong electrostatic forces of attraction between them. But when molten or dissolved ions are free to move and carry charge .

Question 3

What is an anion?

Answer 3

A negatively charged ion

Question 4

What is a cation?

Answer 4

A positively charged ion

Question 5

Which is the anode and which is the cathode?

Answer 5

P ositive
A node
N egative
I s
C athode

Question 6

Describe electrolysis of molten compounds- lead (II) bromide

Answer 6

At the cathode: positive Pb2+ ions are attracted to the negative cathode and a lead ion accepts 2 electrons and is reduced to a lead atom
Pb2+ + 2e- —> Pb
At the anode: negative Br- ions are attracted to the positive anode and 2 bromide ions lose one electron each and are oxidised to form a bromine molecule
2Br- —> Br2 + 2e-

Question 7

Describe electrolysis of aqueous solutions

Answer 7

At the cathode: if the metal is more reactive than hydrogen, then hydrogen gas will be produced. If less reactive, then the metal will be formed

At the anode: if there are Cl-, Br- or I- ions, then these will form molecules. If these aren’t present, then oxygen will be produced
LEARN: 4OH- —> O2 + 2H2O + 4e-

Question 8

Predict the products of electrolysis of aqueous sodium chloride

Answer 8

At the cathode: hydrogen gas will be produced
2H+ + 2e- —> H2
At the anode: chlorine gas will be produced
2Cl- —> Cl2 + 2e-
Used for making bleach and paper
Sodium hydroxide solution also produced, which is used for making soap

Question 9

Predict the product of electrolysis of dilute sulfuric acid

Answer 9

At the cathode: hydrogen gas is produced
2H+ + 2e- —> H2
At the anode: oxygen gas is produced 4OH- —> O2 + 2H2O + 4e-

Question 10

Predict the products of electrolysis of copper (II) sulfate

Answer 10

At the cathode: copper (pink solid) is formed and coats the cathode
Cu2+ + 2e- —> Cu
At the anode: oxygen gas is formed
4OH- —> O2 + 2H2O + 4e-

Question 11

Describe the electrolysis of aluminium oxide

Answer 11

Aluminium formed at cathode and oxygen formed at anode. The anode is made carbon, which reacts with oxygen to form carbon dioxide, so electrode would need replacing. Cryolite can be used to lower mpt

Question 12

When are molecules oxidised and reduced?

Answer 12

Both oxidation and reduction occur in electrolysis. The cations in the electrolyte move towards the cathode and are reduced (gain electrons). The anions move towards the anode and are oxidised (lose electrons).

Question 13

Investigate electrolysis of aqueous solutions

Answer 13

1. Clean two electrode using sandpaper and from this point be careful not to touch them and transfer grease onto them
2. Place both electrodes into a beaker filled with chosen electrolyte
3. Connect the electrodes to a power supply using crocodile clips and wires and you can also connect a bulb too