Question

What is formula unit mass of ${\mathrm{MgCO}}_3$?

Answer 1

Formula unit mass:

• “The formula unit mass of a substance is a sum of the atomic masses of all atoms in a formula unit of a compound.”

Step 1: Finding the Atomic mass of atoms of all elements present in this compound

• Given compound is Magnesium carbonate.
• Atomic mass of Magnesium $\left(\mathrm{Mg}\right)=24\mathrm{u}$
• Atomic mass of Carbon$\left(\mathrm{C}\right)=12\mathrm{u}$
• Atomic mass of oxygen $\left(\mathrm{O}\right)=16\mathrm{u}$

Step 2: Formula used to determine the formula unit mass of ${\mathrm{MgCO}}_3$.

$\text{Formula unit mass of}{\mathrm{MgCO}}_3=\text{Atomic mass of}\mathrm{Mg}+\text{Atomic mass of}\mathrm{C}+(3\times \text{Atomic mass of}\mathrm{O})$

Step 3:Calculation of formula unit mass of ${\mathrm{MgCO}}_3$

$$\begin{gathered} \text{Formula unit mass of}{\mathrm{MgCO}}_3=24\mathrm{u}+12\mathrm{u}+(3\times 16\mathrm{u}) \\ =24\mathrm{u}+12\mathrm{u}+48\mathrm{u} \\ =84\mathrm{u} \end{gathered}$$

Therefore, the formula unit mass of ${\mathrm{MgCO}}_3$ is $84\mathrm{u}$.