Calculate the formula unit mass of ZnO, Na2O and K2CO3. Give atomic mass of Zn = 65u Na = 23u K = 39u C = 12u O = 16u.

Definition.

1. The formula unit mass is the sum of the atomic masses of all the ions present in the formula of the compound multiplied by the number of atoms involved in the compound.
2. It is an important formula used in physical chemistry and used for doing the stoichiometric measurements of ionic as well as covalent solids.
3. Let us suppose a compound A_xB_y, the formula unit mass for this compound is

$\mathrm{Formula}\mathrm{unit}\mathrm{mass}\mathrm{of}{\mathrm{A}}_{\mathrm{X}}{\mathrm{B}}_{\mathrm{Y}}=(\mathrm{atomic}\mathrm{mass}\mathrm{of}\mathrm{A}\mathrm{ion}\times \mathrm{X})+(\mathrm{atomic}\mathrm{mass}\mathrm{of}\mathrm{B}\mathrm{ion}\mathrm{x}\mathrm{Y})$

Given data

1. Atomic mass of Zn = 65u
2. Atomic mass of Na = 23u
3. Atomic mass of K = 39u
4. Atomic mass of C = 12u
5. Atomic mass of O = 16u

i) $\mathrm{ZnO}$

$\mathrm{Formula}\mathrm{unit}\mathrm{mass}\mathrm{of}\mathrm{ZnO}=(\mathrm{atomic}\mathrm{mass}\mathrm{of}\mathrm{Zinc}\mathrm{ion}\mathrm{x}1)+(\mathrm{atomic}\mathrm{mass}\mathrm{of}\mathrm{Oxygen}\mathrm{ion}\mathrm{x}1)$

$=(65\mathrm{x}1)+(16\mathrm{x}1)$

$=81\mathrm{u}$

ii) ${\mathrm{Na}}_2\mathrm{O}$

$\mathrm{Formula}\mathrm{unit}\mathrm{mass}\mathrm{of}{\mathrm{Na}}_2\mathrm{O}=(\mathrm{atomic}\mathrm{mass}\mathrm{of}\mathrm{sodium}\mathrm{ion}\mathrm{x}2)+(\mathrm{atomic}\mathrm{mass}\mathrm{of}\mathrm{Oxygen}\mathrm{ion}\mathrm{x}1)$

$=(23\mathrm{x}2)+(16\mathrm{x}1)$

$=$ $62\mathrm{u}$

iii) ${\mathrm{K}}_2{\mathrm{CO}}_3$

Formula unit mass of ${\mathrm{K}}_2{\mathrm{CO}}_3$ $=(\mathrm{atomic}\mathrm{mass}\mathrm{of}\mathrm{Potassium}\mathrm{ion}\mathrm{x}2)+(\mathrm{atomic}\mathrm{mass}\mathrm{of}\mathrm{Carbon}\mathrm{x}1)+(\mathrm{atomic}\mathrm{mass}\mathrm{of}\mathrm{Oxygen}\mathrm{x}3)$

$=(39\mathrm{x}2)+(12\mathrm{x}1)+(16\mathrm{x}3)$

= 78 + 12 + 48

= 138 u