Buffer solutions can be produced by mixing a weak acid with its conjugate base o

Question

Buffer solutions can be produced by mixing a weak acid with its conjugate base or by mixing a weak base with its conjugate acid. The Henderson-Hasselbalch equation, pH = pK_a + log allows you to calculate the pH of a buffer Note that molarity, moles, and millimoles are all proportional, so you can substitute the number moles, or millimoles for the concentration terms in this formula. Part A You need to produce a buffer solution that has a pH of 5.22 You already have a solution that contains 10. mmol (millimoles)of acetic acid. How many millimoles of acetate (the conjugate base of acetic acid) will you need to add to this solution? The pK_a of acetic acid is 4.74.

Explanation / Answer

pH = pKa + log[base]/[acid]

pH = 5.22

pKa =4.74

[acid] = 10mmoles

[conjugate base]=[acetate] = xmmoles

5.22=4.74+log(x/10)

0.48=log(x/10)

x/10=antilog0.48

x/10 = 3.02

x=30.2

mmoles of acetate=30.02

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