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