Oxidation States

Question 1

What is the usual oxidation of oxygen when it’s combined with another element?

Answer 1

Combined oxygen usually has an oxidation state of -2.

Question 2

What is the oxidation state of hydrogen in H₂?

Answer 2

Hydrogen in H₂ has an oxidation state of 0.

Question 3

Work out the oxidation state of nitrogen in an ammonium ion.

Answer 3

• 3

The NH₄⁺ ion has an overall oxidation state of +1 and H has an oxidation state of +1. So +1 - (+1 × 4) = -3

Question 4

What do oxidation states tell us about atoms?

Answer 4

An atom’s oxidation state tells us how many electrons it has donated or accepted to form an ion or a bond.

Question 5

Lead(II) sulfate(VI) can be made by reacting lead(II) oxide with sulfuric acid. State the oxidation state of:
lead in lead(II) oxide.
[1 mark]

Answer 5

+2

The (II) after the lead in lead(II) oxide tells you this.

Question 6

Lead(II) sulfate(VI) can be made by reacting lead(II) oxide with sulfuric acid. State the oxidation state of:
sulfur in lead(II) sulfate(VI).
[1 mark]

Answer 6

+6

The (VI) after the sulfate in lead(II) sulfate(VI) tells you this.

Question 7

Chromium (Cr) can exist in a range of oxidation states. Give the full name of the compound Cr₂O₃.
[1 mark]

Answer 7

Chromium(III) oxide
Oxygen has an oxidation state of -2.
Total charge from the oxygen = -2 × 3 = -6.
For the overall oxidation state of the compound to be 0, the total charge from the chromium must be +6.
+6 ÷ 2 = +3, so the chromium has an oxidation state of +3.

Question 8

What is the formula of iron(II) nitrate(V)?

[1 mark]

Answer 8

Fe(NO₃)₂
Oxidation state of iron = +2.
Overall oxidation state of nitrate ion = +5 + (-2 × 3) = -1.
So you need a ratio of 1:2 of iron:nitrate to make the compound neutral.