Question

How will you calculate the formula mass of an ionic compound?

Answer 1

Formula mass of an ionic compound:

1. The sum of atomic masses of all the atoms in the ions of an ionic compound is known as the formula mass of an ionic compound.
2. To calculate the formula mass of an ionic compound, add the atomic masses of all the atoms in the formula of an ionic compound.

Example:

1. Sodium chloride $\mathbf{\left(}\mathbf{NaCl}\mathbf{\right)}$ is an ionic compound.
2. It contains one sodium ion $\mathbf{\left(}{\mathbf{Na}}^{\mathbf{+}}\mathbf{\right)}$ and one chloride ion $\mathbf{\left(}{\mathbf{Cl}}^{\mathbf{-}}\mathbf{\right)}$.
3. Thus, the formula mass of Sodium chloride is the sum of the atomic masses of sodium atom $\left(23u\right)$ and chlorine atom $(35.5u)$.
4. Thus, the formula mass of Sodium chloride is $(23+35.5)u$ = $58.5u$.