Question

Calculate

The number of moles

The amount in grammes of HCL that must be added to 500cm^3

Of water to give a solution with pH 3

Answer 1

$[H^+]=10^{-pH}=10^{-3}=0.001\ M$

HCl is a strong monoprotic acid, so [HCl] = [H⁺] = 0.001 M

$n(HCl)=500\ cm^3\times\frac{0.001\ mol}{1\ L}\times\frac{1\ L}{1000\ cm^3}=0.0005\ mol$

$m(HCl) =0.0005\ mol\times\frac{36.46\ g}{1\ mol}=0.0182\ g$

Answer: 0.0005 mol; 0.0182 g