Question

Calculate the molecular mass of Na₂CO_3.

• A. 51 u
• B. 74 u
• C. 130 u
• D. 106 u

Answer 1

The correct option is D

106 u

Molecular mass of a compound is equal to the sum of the masses of its constituent atoms. The atomic mass of sodium, carbon and oxygen are 23 u, 12 u and 16 u respectively.

Therefore, the molecular mass of ${Na}_2{CO}_3$
$=(2\times \text{atomic mass of Na})$ + $(1\times \text{atomic mass of C})$ + $(3\times \text{atomic mass of O)}$
$=(2\times 23)+(1\times 12)+(3\times 16)$
$=46+12+48=106u$.