Question

Calculate the concentration of nitric acid in moles per litre in a sample which has a density, 1.41 g mL^–1and the mass per cent of nitric acid in it being 69%.

Answer 1

Mass percent of nitric acid in the sample = 69 % [Given]

Thus, 100 g of nitric acid contains 69 g of nitric acid by mass.

Molar mass of nitric acid (HNO₃)

= {1 + 14 + 3(16)} g mol^–1

= 1 + 14 + 48

= 63 g mol^–1

∴ Number of moles in 69 g of HNO₃

${\displaystyle =\frac{69 \text{g}}{63 \text{g} {\text{mol}}^{-1}}}$

= 1.095 mol

Volume of 100 g of nitric acid solution

${\displaystyle =\frac{\text{Mass of solution}}{\text{Density of solution}}}$

${\displaystyle =\frac{100 \text{g}}{1.41 {\text{g mL}}^{-1}}}$

${\displaystyle =70.92\text{mL}\equiv 70.92\times {10}^{-3}L}$

Concentration of nitric acid

${\displaystyle =\frac{1.095\text{mole}}{70.92\times {10}^{-3}L}}$

= 15.44 mol/L

∴ Concentration of nitric acid = 15.44 mol/L