3.1.7: Oxidation, Reduction and Redox

Question 1

What is oxidation and reduction?

Answer 1

oxidation- loss of electrons during a reaction or increase in oxidation number
reduction- gain of electrons duing a reaction or decrease in oxidation number

Question 2

What happens in a redox reaction?

Answer 2

reduction and oxidation both occur within a reaction
- electrons are transferred from one species to another

Question 3

What is an oxidation number?

Answer 3

the number representing the no. of electrons lost or gained by an atom in a compound

Question 4

What are the rules to assign a oxidation number?

Answer 4

1. a uncombined element has an oxidation no. of 0
2. a simple ion (single element) has an oxidation no. equal to the charge of zero
3. the sum of the oxidation no.s of the elements in a compound is equal to the overall charge of the compound
4. the charge of a complex ion (e.g. NH4+) is equal to the sum of the oxidation no.s
5. the most electronegative element in a compound always has a negative oxidation no.
6. oxygen always has an oxidation no. of -2 except in peroxides where it’s -1
7. hydrogen always has an oxidation no. of +1 except in metal hydrides where it’s -1

Question 5

What is a half equation?

Answer 5

an equation for a redox reaction which only considers one of the species involved and explicitly shows electrons transferred to or from it

Question 6

What is a reducing and oxidising agent?

Answer 6

reducing agent- a reagent that reduces (adds electrons to) another species, itself losing electrons
oxidising agent- a reagent that oxidises (removes electrons from) another species, itself gaining electrons

Question 7

How do you calculate an ionic equations?

Answer 7

• write balanced half equations (with balanced electron numbers)
• combine equations
• cancel out

if you need oxygen, add H2O. if you need hydrogen, add H+