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 23u, 12u and 16u respectively.

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