Question

Identify the correct increasing order of molecular masses.

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

Answer 1

The correct option is B $\mathrm{CO\; <}{\mathrm{CO}}_2<\mathrm{CaO\; <}{\mathrm{CaCO}}_3$

Molecular mass is the sum of atomic masses of all the atoms in a molecule. Let us see the molecular masses of given molecules:

$\bullet$ 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 $\times$ 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 $\times$ 16)
= 100 u

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