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

`=(69  "g")/(63  "g"  "mol"^-1)`

= 1.095 mol

Volume of 100 g of nitric acid solution

`="Mass of solution"/"Density of solution"`

`=(100  "g")/(1.41  "g mL"^-1)`

`=70.92" mL"-=70.92 xx 10^-3 L`

Concentration of nitric acid

`=(1.095" mole")/(70.92xx10^-3L)`

= 15.44 mol/L

∴ Concentration of nitric acid = 15.44 mol/L