Question

Calculate the relative molecular mass.
(i) Potassium Chlorate [KClO₃]
(ii) Chloroform [CHCl₃]
[H=1, O=16, Cl=35.5, C=12, K=39]

Answer 1

The relative molecular mass of KClO₃ is 122.5 a.m.u, and that of CHCl₃ is 119.5 a.m.u .

• The relative molecular mass of a compound is the sum of the atomic masses of each element multiplied by the respective number of each atom present in the compound.

i) Potassium Chlorate [KClO₃]

• The elements present in KClO₃ are K, Cl, and O.

• The number of atoms of each element present :

K = 1, Cl = 1, O = 3

• Given,

atomic mass of K = 39 a.m.u

atomic mass of Cl = 35.5 a.m.u

atomic mass of O = 16 a.m.u

• Therefore, the relative molecular mass of KClO₃ = (1 × 39) + (1 × 35.5) + (3 × 16)

Or, KClO₃ = 39 + 35.5 + 48

Or, KClO₃ = 122.5 a.m.u (atomic mass unit)

ii)  Chloroform [CHCl₃]

• The elements present in CHCl₃ are C, H, and Cl.

• The number of atoms of each element present :

C = 1, H = 1, Cl = 3

• Given,

atomic mass of C = 12 a.m.u

atomic mass of H = 1 a.m.u

atomic mass of Cl = 35.5 a.m.u

• Therefore, the relative molecular mass of CHCl₃ = (1 × 12) + (1 × 1) + (3 × 35.5)

Or, CHCl₃ = 12 + 1 + 106.5

Or, CHCl₃ = 119.5 a.m.u (atomic mass unit)

Answer 2

Explanation:

Potassium chlorate [KClO3] [K = 39, Cl = 35.5, O= 16]