Question

An acetic acid buffer solution is required to have a pH of 5.27. You have a solution that contains 0.010 mol of Acetic acid. What molarity of sodium acetate will you need to add to the solution

Answer 1

Answer:

Molarity of sodium acetate you will need to add is 0.0324M

Explanation:

Assuming volume of the buffer is 1L.

The pH of a buffer can be determined using Henderson-Hasselbalch equation:

pH = pKa + log [A⁻] / [HA]

Where pKa is pKa of the weak acid,  [A⁻] molar concentration of conjugate base and [HA] molar concentration of weak acid

Replacing for the acetic buffer (pKa = 4.76):

pH = 4.76 + log [Sodium Acetate] / [Acetic Acid]

As you have 0.010 moles of acetic acid in 1L:

[Acetic Acid] = 0.010mol / 1L = 0.010M

And you require a pH of 5.27:

5.27 = 4.76 + log [Sodium Acetate] / [0.010M]

0.51 = log [Sodium Acetate] / [0.010M]

10^0.51 = [Sodium Acetate] / [0.010M]

3.236 =  [Sodium Acetate] / [0.010M]

3.236 [0.010M] = [Sodium Acetate]

0.0324M = [Sodium Acetate]

Molarity of sodium acetate you will need to add is 0.0324M