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The pKa of a weak acid was determined by measuring the pH of a solution containing the weak acid at 0.40 M and its conjugate base at 0.60 M. The measured pH was 7.8. What is the pKa of the weak acid

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Answer:

7.62

Explanation:

Given that :

pH = 7.8

Conjugate base in solution = 0.6 M

Weak Acid in solution = 0.4 M

Recall :

pH = pKa + log(conjugate base / acid)

Hence,

PKa = pH - log(conjugate base / acid)

pKa = 7.8 - log(0.6 / 0.4)

pKa = 7.8 - log(1.5)

pKa = 7.8 - 0.1760912

pKa = 7.6239088

Hence, pKa = 7.62 (2 decimal places)

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