Question

What is the pH of a 1.0 mol/L solution of aqueous sodium hypochlorite?

Answer 1

The pH of a 1.0 mol/L solution of aqueous sodium hypochlorite (NaOCl) depends on the dissociation of sodium hypochlorite in water. When sodium hypochlorite dissolves in water, it forms hypochlorite ions (OCl-) and sodium ions (Na+). The presence of hypochlorite ions in the solution leads to a basic pH.

Sodium hypochlorite is a salt of a weak base (hypochlorous acid, HOCl) and a strong alkali (sodium hydroxide, NaOH), so it undergoes hydrolysis.

The hydrolysis reaction of sodium hypochlorite in water can be represented as follows:

OCl- + H2O ⇌ HClO + OH-

The hypochlorite ion (OCl-) reacts with water to form hypochlorous acid (HOCl) and hydroxide ion (OH-).

Since hypochlorous acid is a weak acid, it partially dissociates in water, resulting in the formation of hydrogen ions (H+) and hypochlorite ions (OCl-):

HOCl ⇌ H+ + OCl-

The presence of hydrogen ions (H+) makes the solution acidic, while the hydroxide ions (OH-) make the solution basic. As long as more hypochlorite ions (OCl-) are present, the solution will be basic.

Therefore, a 1.0 mol/L solution of aqueous sodium hypochlorite will have a basic pH. The exact pH value will depend on additional factors such as temperature and the concentration of hypochlorite ions.