# Quiz | Buffers and Titration of Acids and Bases

1

What is not a condition to apply the Henderson-Hasselbalch equation?

2

Which of the following statements about an acid-base buffer solution is correct?

A buffer solution is an aqueous solution consisting of a mixture of a weak acid and its conjugate base. Its pH changes very little when a small amount of strong acid or base is added to it and does not change when the solution is diluted

3

What is the pH of a buffer solution where [HA] = [A-]?

By definition:   Ka =

If [HA] = [A-], Ka = [H3O+] ⇒ - log Ka = - log [H3O+] ⇒ pKa = pH

4

When is there a big change in pH during a strong acid-strong base titration?

Titration of a strong acid with a strong base: pH changes abruptly at the equivalence point
At the equivalence point: stoichiometrically equivalent amounts of acid and base have reacted

5

What titration corresponds to a titration curve with an initial pH of 9.5 and an equivalence point at pH 4.5?

Initial pH = 9.5 ⇒ weak base
Equivalence point: pH = 4.5 ⇒ Final pH ≈ 9.5 - 2 x 4.5 = 0.5 ⇒ strong acid

6

How many equivalence points do you expect for the titration of H3PO4 with NaOH?

H3PO4 is a polyprotic acid: it can give up to 3 acidic proton:

H3PO(aq) + H2O (l) ⇌ H2PO4(aq) + H3O(aq)
H2PO4(aq) + H2O (l) ⇌ HPO42- (aq) + H3O(aq)
HPO42- (aq) + H2O (l) ⇌ PO43- (aq) + H3O(aq)

3 equivalence points corresponding to the 3 previous acid-base equations are expected for the titration of H3PO4 by a strong base NaOH