Topic 2.1.5 - Redox

What is an oxidation number?

The number of electrons an atom uses to

bond with any other atom

What is the oxidation number

of an uncombined element

such as C, H, O 2 ?

0

What is the oxidation number

of combined oxygen such as

in H 2 O?

-2

What is the oxidation number

of oxygen in peroxides?

-1

What is the oxidation number

of combined hydrogen such as

in NH 3 , H 2 S?

+1

What is the oxidation number

of combined hydrogen in metal

hydrides such as LiH?

-1

What is the oxidation number

of a simple ion?

Charge on the ion

E.g Na + → +1 ; Cl - → -1

What is the oxidation number

of combined fluorine such as

in NaF, CaF 2 ?

-1

When an element has more

than one stable oxidation

number how is it indicated?

Written as a Roman numeral

What is the oxidation number

of Fe in iron (III) chloride?

+3

What are oxyanions?

Negative ions that have an element

along with oxygen

What is the oxidation number

of S in SO 4

2-

?

+6

Because, combined oxygen has an oxidation number of -2.

4 x -2 = -8.

The charge on the compound is -2. Sum of oxidation numbers must

equal -2

So, -2 -(-8) = +6

Define oxidation in terms of

electron transfer and oxidation

number

Oxidation is

● Loss of electrons

● An increase in oxidation number

Define reduction in terms of

electron transfer and oxidation

number

Reduction is

● Gain of electrons

● A decrease in oxidation number

What is a redox reaction?

A reaction in which both oxidation and

reduction takes place

What is the oxidation number

of a metal?

0, because it is an uncombined element