Question

A 1000.-mL solution of hydrochloric acid has a pH of 1.6. Calculate the mass (g) of HCl dissolved in the solution.

Answer 1

Given pH = 1.6

pH = - log [H⁺]

[H⁺] = 10 ^-pH

        = 10 ^-1.6

        = 0.025 M

HCl H⁺ + Cl^-

1 mole of HCl produces 1 mole of H⁺

So [HCl] = [H⁺] = 0.025M

                       = 0.025 mol/L

Given Volume of the solution is = 1000.0 mL = 1 L

So number of moles of HCl in the solution , n = 0.025 mol

Molar mass of HCl = At.mass of H + At.mass of Cl

                            = 1 + 35.5

                            = 36.5 g/mol

We know that Number of moles , n = mass/molar mass

                  So mass of HCl , m = number of moles x molar mass

                                               = 0.025 mol x 36.5 (g/mol)

                                               = 0.917 g

Therefore the mass of HCl dissolved in the solution is 0.917 g