You need to produce a buffer solution that has a pH of 5.40. 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. Express your answer numerically in millimoles. View Available Hint (s)

Question

Imani Dougherty

Chemistry

3 June, 22:21

You need to produce a buffer solution that has a pH of 5.40. 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. Express your answer numerically in millimoles. View Available Hint (s)

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Rebecca Cardenas · Answer 1

46. mmol

Step-by-step explanation:

The equation for the equilibrium is:

HA + H₂O ⇌ A⁻ + H₃O⁺

The solution is a buffer, so we can use the Henderson-Hasselbalch equation:

pH = pKa + log ([A⁻]/[HA])

5.40 = 4.74 + log ([A⁻] / (10.) Subtract 4.74 from each side

0.66 = log ([A⁻] / (10.) Take the antilog of each dide

[A⁻]/10. = 10 ^0.66

[A⁻]/10. = 4.57 Multiply each side by 10.

[A⁻] = 46. mmol

You will add 46. mmol of sodium acetate.