3. Redox (OXIDATION & REDUCTION)

Question 1

Describe what is meant by oxidation

Answer 1

Loss of electrons
Loss of hydrogen
Gain of oxygen

Question 2

Describe what is meant by reduction

Answer 2

Gain of electrons
Gain of hydrogen
Loss of oxygen

Question 3

Describe what is meant by the oxidation number

Answer 3

Oxidation number of an element represents the number of electrons lost or gained

Question 4

Will oxidation number of an element increase or decrease if it is oxidised

Answer 4

The oxidation number will increase if its been oxidised as it has lost electrons
Oxidation number will decrease if its been reduced and gained electrons

Question 5

What is an oxidising agent

Answer 5

A species that oxidises another species by accepting electrons from them so it itself is reduced

Question 6

What is a reducing agent

Answer 6

A species that reduces other species by donating electrons to them so it itself is oxidised

Question 7

Give the rules for assigning oxidation numbers

Answer 7

1. oxidation number of a free element is always 0
2. oxidation numbers of elements in a compound total 0
3. oxidation number of a polyatomic ion is equal to ionic charge

Question 8

Give the oxidation numbers for the following metals:
Group 1 metals
Group 2 metals
Aluminium

Answer 8

Group 1 = +1
Group 2 = +2
Aluminium = +3

Question 9

Give the oxidation numbers for the following non metals:
Oxygen
Hydrogen
Fluorine
Chlorine, Bromine, Iodine

Answer 9

Oxygen = -2 (except peroxide and compounds with fluorine -1 as Fluorine is more electronegative so it needs to be negative)

Hydrogen = +1 except with metal hydrides eg NaH where its -1

Fluorine = -1

Chlorine, Bromine, Iodine = -1 except in compounds with oxygen and fluorine as they are more electronegative so chlorine, bromine and iodine will need to be positive

Question 10

Where are the electrons in a reduction half equation

Answer 10

The left
TIP: redox –> “reduction” is on the left hand side of the word
Cu2+ + 2e- –> Cu

Question 11

Where are the electrons in a oxidation half equation

Answer 11

The right
2Cl –> Cl2 + 2e-

Question 12

What is a disproportionation reaction

Answer 12

Where a species is simultaneously oxidised and reduced at the same time

Question 13

Give the rules to describe how to form more complex half equations

Answer 13

1. add H2O in the products to balance the oxygen
2. add H+ in the reactants to balance the hydrogen
3. add electrons to balance the charge

Question 14

Describe how to combine half equations

Answer 14

1) multiply half equations to get equal amounts of electrons on each side
2) add them together, getting rid of excess H2O and H+ on each side