Atoms and Molecules - Formula Unit Mass of Ionic Compounds

Calculate the formula unit mass of Zinc Oxide ($ZnO$). (Given: Atomic mass of $Zn = 65\ u$, $O = 16\ u$)

$Formula\ unit\ mass\ of\ ZnO = (1 \times 65\ u) + (1 \times 16\ u)$ $\begin{array}{r} 65 \\ + 16 \\ \hline 81 \end{array}$ Total mass = $81\ u$.

Since the formula $ZnO$ contains one atom of Zinc and one atom of Oxygen, we add their respective atomic masses together.

Calculate the formula unit mass of Calcium Chloride ($CaCl_{2}$). (Given: Atomic mass of $Ca = 40\ u$, $Cl = 35.5\ u$)

$Mass\ of\ Ca = 1 \times 40 = 40\ u$ $Mass\ of\ 2 \times Cl = 2 \times 35.5 = 71\ u$ Total: $\begin{array}{r} 40 \\ + 71 \\ \hline 111 \end{array}$ Total mass = $111\ u$.

In $CaCl_{2}$, there is one Calcium ion and two Chloride ions. We multiply the mass of Chlorine by $2$ and add it to the mass of Calcium.

Find the formula unit mass of Potassium Carbonate ($K_{2}CO_{3}$). (Given: $K = 39\ u, C = 12\ u, O = 16\ u$)

$Mass\ of\ 2 \times K = 2 \times 39 = 78\ u$ $Mass\ of\ 1 \times C = 1 \times 12 = 12\ u$ $Mass\ of\ 3 \times O = 3 \times 16 = 48\ u$ Total: $\begin{array}{r} 78 \\ 12 \\ + 48 \\ \hline 138 \end{array}$ Result: $138\ u$.

The formula $K_{2}CO_{3}$ consists of two Potassium atoms, one Carbon atom, and three Oxygen atoms. Summing these masses gives the formula unit mass.