#### Question

Concentrated nitric acid used in laboratory work is 68% nitric acid by mass in aqueous solution. What should be the molarity of such a sample of the acid if the density of the solution is 1.504 g mL^{−1}?

#### Solution

Concentrated nitric acid used in laboratory work is 68% nitric acid by mass in an aqueous solution. This means that 68 g of nitric acid is dissolved in 100 g of the solution.

Molar mass of nitric acid (HNO_{3}) = 1 × 1 + 1 × 14 + 3 × 16 = 63 g mol^{−1}

Then, number of moles of HNO_{3 } = `68/63` mol

=1.079 mol

Given,

Density of solution = 1.504 g mL^{−1}

∴ Volume of 100 g solution = `100/1.504 mL`

=66.49 mL

=66.49x10^{-3} L

Molarity o Solution = `(1.079 "mol")/(66.49xx10^(-3)L)`

=16.23 M

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Solution Concentrated nitric acid used in laboratory work is 68% nitric acid by mass in aqueous solution Concept: Expressing Concentration of Solutions.