Question

(a) Deine the term ‘molecular mass’. 

(b) Determine the molecular mass of ZnSO₄ .

[Atomic mass of Zn = 65 u, S = 32 u, O = 16 u]

Answer 1

a) Molecular mass: The molecular mass of a substance is the sum of atomic masses of all the atoms in a molecule of the substance. 

i. It is used for those substances whose constituent particles are molecules. 

ii. The molecular mass remains the same even if millions of molecules are added.

iii. For example: The molecular mass of H₂O = 2 × Atomic mass of hydrogen + Atomic mass of oxygen 

= 2 + 16 = 18u 

b) Molecular mass of ZnSO₄ : 

Atomic mass of Zn + Atomic mass of S + 4× atomic mass of O

65 u + 32 u + 4× 16u

65 u + 32 u + 64 u 161 u 

Thus, the molecular mass of ZnSO₄ is 161u