The following questions a24 - a26 relate to 100 ml of 0.0150 m solution of benzoic acid (c6h3cooh). ka(c6h3cooh) = 6.4 x 10^-5. what is the ph of the solution after the addition of 1 x 10^-3 moles of naoh? you may assume no volume change to the solution upon addition of the naoh.

PH of the weak acid: approximately 2.513.

PH of the buffer solution: approximately 4.495.

Explanation:

The Ka value of benzoic acid is much smaller than 1. Benzoic acid will dissociate but only partially when dissolved in water. Construct a RICE table for this process. Let the equilibrium of be . Note that .

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Solve this quadratic equation for :

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Take only the non-negative root. .

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Each benzoic acid contains only one carboxyl group . Benzoic acid is thus a monoprotic acid. Each mole of the acid will react with only one mole of . The 100 mL solution initially contains moles of benzoic acid. The moles of will neutralize only part of the acid. The solution will eventually contain moles of (from the salt ) and moles of .

Both the acid and the conjugate base of the acid exist in large amounts in the solution. Apply the Henderson-Hasselbalch equation for weak acid buffers to find the pH of this buffer solution.

for benzoic acid.

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