Practice Oxidation Number in Chemistry

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

Quick Recap

A number assigned to each atom in a compound using a set of rules, representing the hypothetical charge that atom would carry if all bonds were treated as fully ionic (all shared electrons assigned to the more electronegative atom).

An imaginary 'electron bookkeeping' system. If an atom 'owns' more electrons than usual, its oxidation number is negative; fewer means positive.

Showing a random 20 of 50 problems.

Example 1

easy
What is the oxidation number of fluorine in any compound?

Example 2

easy
Oxidation number of oxygen in peroxide H2O2H_2O_2?

Example 3

medium
Find the oxidation number of Cl in HClO4\text{HClO}_4.

Example 4

challenge
In 2H2+O2โ†’2H2O2H_2 + O_2 \rightarrow 2H_2O, identify which element is oxidized.

Example 5

medium
Find the oxidation number of I in IO3โˆ’\text{IO}_3^-.

Example 6

medium
Assign oxidation numbers to each atom in KMnO4\text{KMnO}_4 and determine the oxidation number of manganese.

Example 7

easy
Oxidation number of oxygen in H2OH_2O?

Example 8

medium
Find the oxidation number of V in VO2+\text{VO}_2^+.

Example 9

easy
What is the oxidation number of an element in its pure form, e.g. O2O_2?

Example 10

medium
Find the oxidation number of C in CO\text{CO}.

Example 11

medium
Find the oxidation number of S in Na2S2O3\text{Na}_2\text{S}_2\text{O}_3 (average per S).

Example 12

easy
Find the oxidation number of hydrogen in NaH\text{NaH}.

Example 13

medium
Find the oxidation number of C in CH3OH\text{CH}_3\text{OH} (methanol).

Example 14

medium
Find the oxidation number of S in SO2SO_2.

Example 15

hard
Find the oxidation number of Mn in MnO2\text{MnO}_2.

Example 16

medium
Find the oxidation number of Cr in Cr2O72โˆ’Cr_2O_7^{2-}.

Example 17

medium
Is oxidation number the same as ionic charge in CH4CH_4?

Example 18

medium
Find the oxidation number of P in H3PO4\text{H}_3\text{PO}_4.

Example 19

hard
In the reaction Fe2O3+3COโ†’2Fe+3CO2\text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2, determine the oxidation number of iron and carbon on each side. Which element is oxidized and which is reduced?

Example 20

easy
Find the oxidation number of Al in Al2O3\text{Al}_2\text{O}_3.