To perform an analysis, a chemist needed to control the pH of the medium between 4.00 and 5.00 throughout the experiment

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To perform an analysis, a chemist needed to control the pH of the
medium between 4.00 and 5.00 throughout the experiment. For this, he prepared 1.0 L of a buffer solution consisting of a mixture of 4.67 g of phenylacetic acid (HA) and 12.43 g of sodium phenylacetate (NaA).
a) Determine the pH of the resulting buffer solution. (Consider that the
added substances remain in the same form in the solution).

b) At one point in the experiment, the chemist needed to add
20.0 mL of a 0.500 mol L-1 NaOH solution. What will be the new pH of the
system?

c) Based on the results obtained in items (a) and (b), it can be stated that the
Is the chosen buffer solution suitable for the experiment?
Justify.
Data:

Phenylacetic acid (HA): Ka = 4.90 x 10-5

MM phenylacetic acid (HA) = 136.15 g mol-1

MM sodium phenylacetate (NaA) = 158.13 g mol-1