Question

The formula unit masses of CaS and MgS are _____ and _____ respectively.
[Atomic masses of Ca, Mg and S are 40 u, 24 u and 32 u respectively.]

Answer 1

The formula unit mass of $CaS$
$=(1\times \text{atomic mass of Ca})$ + $(1\times \text{atomic mass of S})$
$=(1\times 40u)+(1\times 32u)$
$=72u$


The formula unit mass of $MgS$
$=(1\times \text{atomic mass of Mg})$ + $(1\times \text{atomic mass of S})$
$=(1\times 24u)+(1\times 32u)$
$=56u$