Hypochlorous acid HOCL is the active ingredient in most blea

Hypochlorous acid (HOCL) is the active ingredient in most bleach and is one of the most common disinfectants for water. This acid has a pKa of 7.60. A solution of HOCL is prepared in water by adding 15 mg HOCL to a bottle containing 1 L of water. The final pH is measured to be 7.0. What are the molar concentrations of HOCL and OCL-?

Please show full work!

Solution

pH = 7.0

pKa = 7.60

pH = pKa + log [salt / acid]

7.0 = 7.60 + log [OCL- / HOCL]

[OCL- / HOCL] = 0.2512

mass of HOCl = 15 mg = 0.015 g

moles of HOCL = 0.015 / 52.46 = 2.86 x 10^-4 mol

Molar concentration of HOCL = 2.86 x 10^-4 M

Molar concentration of OCL- = 7.18 x 10^-5 M