Calculate the pH of a solution that is 0.240 M in sodium formate (HCOONa) and 0.120 M in formic acid (HCOOH). Express your answer to two decimal places.

Answer : The  pH of the solution is, 4.0

Explanation : Given,

Acid dissociation constant for formic acid,

Concentration of formic acid (acid) = 0.120 M

Concentration of sodium formate (salt) = 0.240 M

First we have to calculate the value of .

The expression used for the calculation of is,

Now put the value of in this expression, we get:

Now we have to calculate the pH of buffer.

Using Henderson Hesselbach equation :

Now put all the given values in this expression, we get:

Thus, the pH of the solution is, 4.0