A 1.50 L buffer solution is 0.250 M in HF and 0.250 M in NaF. Calculate the pH of the solution after the addition of 0.100 moles of solid NaOH. Assume no volume change upon the addition of base. The Ka for HF is 6.8 × 10-4.

Answer : The pH of the solution is, 3.41

Explanation :

First we have to calculate the moles of .

Now 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:

The reaction will be:

Initial moles     0.375     0.100   0.375

At eqm.   (0.375-0.100)      0     (0.375+0.100)

                     = 0.275                    = 0.475

Now we have to calculate the pH of solution.

Using Henderson Hesselbach equation :

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

Thus, the pH of the solution is, 3.41

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