How many moles of solid NaF would have to be added to 1.0 L of 0.115 M HF solution to achieve a buffer of pH 3.46? Assume there is no volume change. Ka for HF = 7.2 × 10 –4

Answer : The  moles of solid NaF is, 1.09 mole.

Explanation : Given,

pH = 3.46

Concentration of HF = 0.115 M

Volume of solution = 1.0 L

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 moles of HF.

Now we have to calculate the moles of NaF.

Using Henderson Hesselbach equation :

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

Thus, the moles of solid NaF is, 1.09 mole.