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=pKa+log[base][acid]

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 5.12. 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 pKa of acetic acid is 4.74

Explanation / Answer

pH=pKa+log{[acetate]/[acetic acid] }

since volume is same, concentartion term can be replaced by numer of moles
pH=pKa+log{n(acetate)/ n(acetic acid) }
5.12 = 4.74 + log {n(acetate) / 10}
n(acetate)/10 = 2.4
n(acetate) = 24 mmol
Answer: 24 mmol

Related Questions

Navigate

• Browse (All)
• Browse B
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.