The pH at 25 °C of an aqueous solution of the sodium salt of p-monochlorophenol (NaC6H4ClO) is 11.05. Calculate the concentration of C6H4ClO- in this solution, in moles per liter. Ka for HC6H4ClO is equal to 6.6×10-10.

Approximately .

Explanation:

The in this question refers the dissociation equilibrium of as an acid:

.

.

However, the question also states that the solution here has a of , which means that this solution is basic. In basic solutions at , the concentration of ions is considerably small (typically less than .) Therefore, it is likely not very appropriate to use an equilibrium involving the concentration of ions.

Here's the workaround: note that is the conjugate base of the weak acid . Therefore, when dissociates in water as a base, its would be equal to . ( is the self-ionization constant of water. at .)

In other words,

.

And that value corresponds to the equilibrium:

.

.

The value of has already been found.  

The concentration of this solution can be found from its value:

.

To determine the concentration of , consider the following table:

Before hydrolysis, the concentration of both and are approximately zero. Refer to the chemical equation. The coefficient of and are the same. As a result, this equilibrium will produce and at the exact same rate. Therefore, at equilibrium, .

Calculate the equilibrium concentration of from :

.

b. is the answer hoped i