3.07 Electrolysis

Question 1

What is electrolysis?

Answer 1

The process of breaking down a substance using electricity

Question 2

What is an electrolyte?

Answer 2

The liquid that is required to conduct electricity

Question 3

How do electrolytes conduct electricity?

Answer 3

The contain free ions (that are either molten or dissolved) - it is these that conduct electricity

Question 4

What is an electrode?

Answer 4

A solid that conducts electricity and that is submerged into the electorlyte

Question 5

WHich electrodes do the positive and negative ions in an electrolyte go towards? Then what happens?

Answer 5

Positive ions (cations) go to the negative electrode (cathode) and gain electrons

Negative ions (anions) go to positive electrode (anode) and lose electrons

The ions then become atoms or molecles and are released (discharged) from the electrolyte

Question 6

What is reduction in electrolysis and where does it happen?

Answer 6

Reduction = positive ions gaining electrons.

Occurs at the negative electrode (cathode)

Question 7

What is oxidation in electrolysis and where does it happen?

Answer 7

Oxidation = negative ions losing electrons

Occurs at positive electrode (anode)

Question 8

WHat type of material should electrodes be made out of? Give two examples.

Answer 8

Inert materials, e.g. graphite, platinum

Question 9

What is a binary compound?

Answer 9

An ionic compound containing two elements which are ions (a +ve metal ion and a -ve non-metal ion)

Question 10

What does electrolysis of molten lead bromids (PbBr2) make?

Answer 10

Lead and bromine

Question 11

What are half equations?

Answer 11

Half equations show how electrons are transferred during the reactions at each electrode

Question 12

In general, what is the process for writing a half equation?

Answer 12

1. Write the symbole for one of the ions on the left side of the equation
2. Write the symbol for the corresponding neutral atom or molecule ont he right side of the equation
3. Balance the number of atoms in the equation
4. Balance the charges on each side by adding or subtracting electrons (shown as e- )

Question 13

For the electrolysis of molten lead bromide, write the half equation at the negative electrode (using the usual process).

Answer 13

Note: Negative electrode attracts the +ve charged lead ions

1. Pb2+
2. Pb2+ —-> Pb
3. Number of atoms already balanced
4. The charge on the left is 2+ so needs to electrons to make it neutral, thus:

Pb2+ + 2e- —-> Pb

Question 14

For the electrolysis of molten lead bromide, write the half equation at the positive electrode (using the usual process).

Answer 14

Note: positive electrode attractgs the -ve charged bromide ions

1. Br-
2. Br- —-> Br2
3. 2Br- —-> Br2
4. THe charge on the left is 2-, so the right needs two electrons to balance the charge, so:

2Br- —-> Br2 + 2e-

Question 15

What would you see at the electrodes during electrolysis of molten lead bromide?

Answer 15

1. brown vapour of bromine gas at anode
2. silver liquid at the cathod as molten lead is formed