Question

The molecular formula of calcium chloride is ${\mathrm{CaCl}}_2$ . What is the molecular weight of this drug?

Answer 1

Step1. Molecular weight

• Molecular weight is the sum of atomic weight, measured in amu.
• The mass of one carbon atom is equal to the atomic mass unit (formerly abbreviated as 'amu,' but now spelled as 'u' – unified mass) according to the latest IUPAC recommendation.

Step 2. Calculation of molecular weight of ${\mathrm{CaCl}}_2$

• Calcium chloride $\left({\mathrm{CaCl}}_2\right)$ has one atom of Calcium and two atoms of Chlorine.
• Molecular weight of ${\mathrm{CaCl}}_2$ =

$$\begin{gathered} {\text{Molecular weight of CaCl}}_2\text{=The atomic weight of Ca+2×Atomic weight of Cl} \\ =\left(1\times 40+2\times 35.5\right){\text{g mol}}^{-1} \\ {\text{=111 g mol}}^{-1} \end{gathered}$$

Hence the molecular weight of ${\mathrm{CaCl}}_2$ is $111\mathrm{g}{\mathrm{mol}}^{-1}$.