Asked by Josh

A 25.00 mL sample of a soft drink was titrated using 12.10 mL of 1.50 M NaOH. Given that the soft drink's monoprotic acid has a Ka value of 2.8 x 10^-5, predict the pH of the soft drink.

I know that the answer is pH 2.85 (our practice questions have an answer key) but I'm really struggling to understand how to do the question. If anyone could help I would be super grateful. Thanks!
Answered by DrBob222
Call the soft drink, since it is monoprotic, HA.
Then HA + NaOH ==> NaA + H2O
mols NaOH = M x L = 0.0121 x 1.5 = ?
mols HA = the same because of the 1:1 ratio in the balanced equation.
M HA = mols HA/L HA or M HA = approx 0.7 but yu need a better answer than that estimate. Then

........HA ==> H^+ + A^-
I......0.7M....0.....0
C......-x......x.....x
E....0.7-x.....x.....x

Ka = 2.8E-5 = (x)(x)/(0.7-x)
Solve for x and convert to pH. I worked through it and 2.85 for pH is right.
There are no AI answers yet. The ability to request AI answers is coming soon!