Topic 3 Redox I

Question 1

What is reduction and oxidation?

Answer 1

Electrons are transferred when reduction and oxidation occurs.
OILRIG
Oxidation is the Loss of electrons
Reduction is the gain of electrons

Question 2

What is a redox reaction?

Answer 2

This is when reduction and oxidation happen at the same time.

Ca + 1/2 O2 —-> CaO is a redox reaction

Ca—-> Ca2+ + 2e- Calcium is being oxidised as it is losing electrons

1/2 O2 +2e- —–> O2- oxygen is being reduced as it is gaining electrons

Question 3

What are reducing agents and oxidising agents?

Answer 3

They lose electrons and are oxidised themselves
They gain electrons and are reduced themselves

Question 4

What are the oxidation number rules?

Answer 4

Uncombined elements are always 0

Oxidation number is same as charge on the ion

Group 1 and 2 is always +1 and +2

Aluminium is always +3

Hydrogen is always +1 except in hydrides where it is -1.

Chlorine is always -1 except if it is in a compound with F and O, it would have a positive value

Fluorine is always -1

Oxygen is -2 except it is -1 in peroxides and +2 in OF2

Question 5

What is oxidation and reduction in terms of numbers?

Answer 5

Oxidation is an increase in the oxidation number
Reduction is a decrease in the oxidation number

Question 6

Rules for balancing half equations?

Answer 6

Write down the species before and after a reaction
Balance any atoms apart from oxygen and hydrogen
Balance any oxygens with H2O
Balance any hydrogens with H+
Balance charges with electrons e-

Question 7

How to combine half equations to make a full ionic equation

Answer 7

Write them both out and then make sure the electrons balance. Do this by multiplying the entire equations.

Then cancel the electrons and combine the 2 equations

Your full ionic equation shows both reduction and oxidation and so is a redox reaction

Question 8

What is a disproportionation reaction?

Answer 8

This is when reduction and oxidation simultaneously happens