3.1.7 Oxidation, reduction and redox equations

Question 1

What is oxidation?

Answer 1

Oxidation is a loss of electrons

OIL

Question 2

What is reduction?

Answer 2

Reduction is a gain of electrons

RIG

Question 3

What happens to an oxidising agent?

Answer 3

An oxidising agent accepts electrons, therefore it is reduced

Question 4

What happens to a reducing agent?

Answer 4

A reducing agent donates electrons, therefore it is oxidised

Question 5

What is an oxidation state?

Answer 5

Tells you the total number of electrons that have been donated or accepted.

Question 6

When are oxidation states positive?

Answer 6

When the atom has donated electrons, is oxidised/ acts as a reducing agent

Question 7

When are oxidation states negative?

Answer 7

When the atom accepts electrons, is reduced/ acts as an oxidising agent

Question 8

What is the oxidation state of uncombined elements?

E.g. He and Ar

Answer 8

Uncombined elements have an oxidation state of 0

Question 9

What is the oxidation state of elements bonded to identical atoms?

E.g. O₂ or H₂

Answer 9

Elements bonded to identical atoms have an oxidation state of 0

Question 10

What is the oxidation state of a monotomic ion?

E.g. Na+

Answer 10

The oxidation state of a monotomic ion is the same as its charge

E.g. Na+ has an oxidation state of +1

Question 11

What is the overall oxidation state of complex ions?

E.g. SO₄^2-

Answer 11

The overall oxidation state of a complex ion is just the ion charge

Question 12

In a compound ion which element has a negative oxidation state?

Answer 12

The most electronegative element has a negative oxidation state, The other elements have more positive oxidation states

Question 13

What is the oxidation state for a neutral compound

E.g. Fe₂O₃

Answer 13

The overall oxidation state will be 0 for a neutral compound

Question 14

What is the oxidation state of oxygen? What is the exception?

Answer 14

Combined oxygen is nearly always -2

Except in peroxides where it’s -1

And O₂ where it’s 0

Question 15

What is the oxidation state of hydrogen? What is the exception?

Answer 15

Combined hydrogen is nearly always +1

Except in metal hydrides where it’s -1

And H₂ where it’s 0

Question 16

Explain how to combine half equations?

Answer 16

1. Make sure atoms and charges balence
2. Make sure both equations have the same number of electrons, this may involve multiplying one or both equations by the amount to ensure that the number of electrons is the same
3. Combine the half equations
4. Electrons arent included in the full equation and there should be the same number of e^- on either side so cancel them out