Question

In the formula mass of $Ca(N{O}_3{)}_2$, find the approximate percentage of oxygen?

• A. $28$
• B. $42$
• C. $58$
• D. $68$
• E. $84$

Answer 1

The correct option is C $58$

The molar mass of $Ca(N{O}_3{)}_2=40.1+2\times (14+3\left(16\right))=40.1+2\times (62)=164.1g/mol$.
1 mole (164.1 g) of calcium nitrate will contain 6 moles of O atoms.
The atomic mass of oxygen is 16 g/mol.
6 moles of oxygen atoms corresponds to $6\times 16=96g$.
The percent of oxygen in calcium nitrate $=\frac{96\times 100}{164.1}=58$ %.