Question

Calculate the formula unit mass of $ZnO,N{a}_{2}O\text{and}{K}_{2}C{O}_3$ respectively.
Given atomic mass of
$Zn=65uNa=23uK=39uC=12uO=16u$

• A. None of the above
• B. 62 g, 81 g, 138 g
• C. 81 u, 62 u, 138 u
• D. 81 u, 81 u, 138 u

Answer 1

The correct option is C 81 u, 62 u, 138 u

Formula unit mass is defined as the sum of the atomic masses of all atoms that are present in a formula unit of the given compound.
Atomic mass of
$Zn=65uNa=23uK=39uC=12uO=16u$

Calculating the formula unit masses of the given compounds:
$ZnO=Zn+OZnO=(65+16)u=81uN{a}_{2}O=\left[\right(2\times 23)+16]uN{a}_{2}O=(46+16)u=62u{K}_{2}C{O}_3=2k+C+3O{K}_{2}C{O}_3=\left[\right(2\times 39)+12+(3\times 16\left)\right]u{K}_{2}C{O}_3=(78+12+48)u=138u$

Hence, the formula unit mass of $ZnO$ is 81 u, $N{a}_{2}O$ is 62 u and $K_{2}C{O}_3$ is 138 u.

Thus, option (a) is correct.