7.1 Oxidation and reduction

Question 1

Where does the term redox come from

Answer 1

reduction-oxidation

Question 2

What did oxidation mean historically

Give equations for it with copper

Answer 2

Oxidation meant the gain of oxygen, so when an element gains oxygen it is oxidised

Cu(s) +1/2O2 —> CuO(s)

Question 3

What is reduction historically

Give an equation of copper oxide being reduced, what reduces it?

Answer 3

A reaction where oxygen is removed

In this reaction, hydrogen is the reducing agent

CuO(s) +H2 —> Cu(s) + H20(l)

So the addition of hydrogen is called reduction

Question 4

Reaction of chlorine being reduced by hydrogen

Answer 4

Cl2(g) + H2(g) –> 2HCl(g)

Question 5

What is a redox reaction in terms of electrons

Answer 5

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When something is oxidised it loses electrons and when something is reduced it gains electrons.

This is why they’re called electron transfer reactions

Question 6

The equation between copper and oxygen forms copper oxide

Cu(s) + 1/2O2(g) –> CuO(s)

What would the half equation be for copper, and what would it be for oxygen

Answer 6

Cu –> Cu2+ + 2e-

1/2O2 + 2e- —> O2-
The charges have to be equal on both sides

Question 7

How would you end up with an original equation from two half equations

Eg the two half equations from Copper oxide

Cu —> Cu2+ + 2e-
1/2O2 + 2e- —> O2-

Answer 7

You add the two half equations together to get the original one.

The electrons must cancel out

Question 8

What is a spectator ion

Answer 8

An ion that takes no part in a reaction