Question

Calculate the concentration of nitric acid in moles per litre in a sample which has a density, 1.41 g mL–1 and 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
= $\frac {69 \ g}{63 \ g\ mol^{-1}}$
= 1.095 mol
Volume of 100g of nitric acid solution
= $\frac {\text {Mass \ of\ solution} }{\text {density\ of\ solution}}$

= $\frac {100 \ g }{1.41\ g ML^{-1}}$
= 7$0.92$ mL
= $70.92×10^{-3}$ L
= $15.44$ mol/L
∴ Concentration of nitric acid = $15.44$ mol/L