The Ka of hypochlorous acid (HClO) is 3.00*10^-8. What is the pH at 25.0 °C of an aqueous solution that is 0.02M in HClO?​

Approximately .

Explanation:

Hypochlorous acid ionizes partially at room temperature:

.

The initial concentration of in this solution is .

Construct a table to analyze the concentration (also in ) of the species in this equilibrium.

The initial concentration of is negligible (around ) when compared to the concentration of .

Let be the reduction in the concentration of at equilibrium when compared to the initial value. Accordingly, the concentration of and would both increase by . ( since concentration should be non-negative.)

.

Let , , and denote the concentration of the three species at equilibrium respectively. Equation for the of :

.

Using equilibrium concentration values from the table above:

.

.

Since is a weak acid, it is reasonable to expect that only a very small fraction of these molecules would be ionized at the equilibrium.

In other words, the value of (concentration of that was in ionized state at equilibrium) would be much smaller than (initial concentration.)

Hence, it would be reasonable to estimate as :

.

Solve for with the simplifying assumption:

.

When compared to the actual value of (calculated without the simplifying assumption,) this estimate is accurate to three significant figures.

In other words, the concentration of in this solution would be approximately at equilibrium.

Hence the :

.

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