Question

Arrange the molecules in the increasing order of molecular weight from top to bottom.

• A. $\mathrm{CO}$
• B. ${\mathrm{CO}}_2$
• C. $\mathrm{CaO}$
• D. ${\mathrm{CaCO}}_3$

Answer 1

Molecular weight is the sum of atomic weight of individual atoms constituting a molecule.

$\bullet$ Molecular weight of CO = atomic weight of C + atomic weight of O = 12 + 16 = 28 u.

$\bullet$ Molecular weight of ${\text{CO}}_2$ = atomic weight of C + (2 $\times$ atomic weight of O) = 12 + 2 x 16 = 44 u.

$\bullet$ Molecular weight of CaO = atomic weight of Ca + atomic weight of O = 40 + 16 = 56 u.

$\bullet$ Molecular weight of ${\text{CaCO}}_3$ = atomic weight of Ca + atomic weight of C + (3 $\times$ atomic weight of O) = 40 + 12 + 3 x 16 = 100 u.

Hence, the increasing order of molecular weight is
$CO$ < $C{O}_2$ < $CaO$ < $CaC{O}_3$