Titration calculations with butanoic acid and Lithium hydroxide

Question

Butanoic acid, HC4H7O2, has a Ka = 1.50x10-5. Butanoic acid was titrated with Lithium hydroxide. If 150.0 mL of 0.15M butanoic acid was titrated with 0.75M lithium hydroxide

(00) draw the Lewis dot structure for butanoic acid

(0) is butanoic acid monoprotic? if so, which proton is the acidic proton?

(a) what volume of lithium hydroxide was required to reach the equivalence point? (b) calculate the initial pH of the butanoic acid

(c) calculate the pH at 15.0 mL LiOH added

(d) calculate the pH at 20.0 mL LiOH added

(e) calculate the pH at the equivalence point

(f) calculate the pH at 5.0 mL past the equivalence point

(g) which indicator would be the best for this titration? Explain

(h) plot a rough graph of your results on the graph provided

Answer 1

A word to the wise...don't ask such lengthy questions all at once. It is daunting to read such a question and try to answer all parts in one sitting. I'll get you started, and hopefully you can finish. If not, post again with individual parts.

I can't draw a Lewis dot structure on this platform, but butanoic acid is CH3CH2CH2COOH (HC4H7O2) where the -COOH is actually a -C=O with an -OH also attached to this carbon.

Butanoic acid is a monoprotic acid and the proton which is acidic is the one on the COOH.(the bolded one).

(a) HC4H7O2 + LiOH ==> LiC4H7O2 + H2O

Initial moles butanoic acid = 0.15 L x 0.15 mol/L = 0.0225 moles

Volume LiOH needed for neutralization (equivalence): (x L)(0.75 mol/L) = 0.0225 mol and x = 0.03 L = 30 mls

(b) Initial pH of butanoic acid: Ka = [H+][C4H7O2-] / [HC4H7O2]

1.5x10^-5 = (x)(x) / 0.15

x = 1.5x10-3 M = [H+]

pH = -log [H+]

pH = 2.82

For the remainder of additions of LiOH, you will form a buffer. So figure out moles butanoic acid remaining, moles of butanoate salt formed and use the Henderson Hasselbalch equation to find the pH.

pH = pKa + log [buntanoate salt]/[butanoic acid]