If you want a solution to maintain a pH= 7.9 which would be a better choice...

If you want a solution to maintain a pH= 7.9 which would be a better choice for the buffer pKa = 8.07 or acetic acid pKa = 4.8?

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Expert Solution

pH of the buffer depends on the concentration of the acid, concentration of conjugate base and the pKa of the acid.

This relation is given by the Henderson-Hasselbalch equation

Where are the concentration of conjugate base and acid respectively. pKa is the pKa of the acid.

For a solution to maintain pH=7.9, we would want an acid whose pKa is closer to 7.9.

This is because, with addition of a small amount of strong acid or base, the concentration of our acid and conjugate base changes. With addition of acid, the cojugate base is consumed and converted to the weak acid. WIth additon of base, the acid is converted to conjugate base. But if the dissociation constant Ka is high (which is the case with lower pKa) , the change in concentration is high.

We want our buffer to tolerate small addition of acid and base. But if we take the acid with pKa 4.8, the pH of the solution will fluctuate too much with away from 7.9.

Hence, the better choice will be the pKa of 8.07 as it is very close to 7.9. Hence, the solution can tolerate addition of small amount of acid or base.

queen_honey_blossom answered 1 year ago

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