Question

1. Calculate the pH of a buffer system that is 0.40M acetic acid (CH3COOH)? and 0.45M sodium acetate (NaCH3COO). You must write the Henderson-Hasselbach equation for this system and show your work.

2. What pH do you obtain when you add 1.0M potassium hydroxide (KOH) to 1.0 M acetic acid (CH₃COOH)? You must give the balanced chemical reaction and show your work.

3.Which of the following buffer systems would you choose if you want to make a buffer of pH 4.7?

Answer 1

1-

We know a buffer is a solution where both a weak acid and its conjugate base are present. Now the pH of a buffer is calculated by the Henderson Hasselblach equation-

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

Now in the given buffer, we have-

weak acid = CH3COOH

conjugate base = CH3COO^- (from NaCH3COO -----------> CH3COO^- + Na⁺)

pKa for acetic acid = 4.74

[weak acid] = [CH3COOH] = 0.40 M

[conjugate base] = [CH3COO^-] = [NaCH3COO] = 0.45 M

Now putting the values in-

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

= 4.74 + log [0.45 M] / [ 0.40 M]

= 4.74 + log [1.125‬]

= 4.74 + 0.05

= 4.79