Problems on determination of Oxidation Number

Problems on determination of Oxidation Number

ON of neutral molecule is always zero

Illustration 1 – Oxidation Number of H and O in H2O

Let us take ON of H = +1 and ON of O = -2

2 X (+1) + 1 X (-2) = 0

(+2) + (-2) = 0 thus, ON of H is +1 and ON of O is -2

Illustration 2 – Oxidation Number of Na and Cl in NaCl

ON of Na = +1 and ON of Cl = -1

(+1) + (-1) = 0 thus, ON of Na is +1 and ON of Cl is -1

Illustration 3 – Oxidation Number of S in H2SO4

Let ON of S be (x) and we know ON of H = +1 and O = -2

2 X (+1) + (x) + 4 X (-2) = 0

(+2) + (x) + (-8) = 0

(x) = +6 therefore, ON of S is +6

Illustration 4 – Oxidation Number of Cr in K2Cr2O7

Let ON of Cr be x and we know ON of K = +1 and O = -2

2 X (+1) + 2 X (x) + 7 X (-2) = 0

(+2) + (2x) + (-14) = 0

2x = +12

x = +6 therefore, ON of Cr in K2Cr2O7 is +6

Illustration 5 – Oxidation Number of Fe in FeSO4

Let ON of Fe be x and we know ON of S = +6 and O = -2

42.   + 1 X (+6) + 4 X (-2) = 0

43.   + (+6) + (-8) = 0

x = +2 therefore, ON of Fe in FeSO4 is +2

Problems:

1. Find the oxidation number of Mn in KMnO4

2. Find the oxidation number of Cr in Na2Cr2O7

3. Find the oxidation number of Cu in CuSO4

4. Find the oxidation number of Fe in FeO