Titration multiple choice 2011 hsc q 15 (1 Viewer)

[tlv6554]

Heres the question:
Using 0.100 mol L–1 NaOH, a student titrated 25.0 mL of a 0.100 mol L–1 weak
monoprotic acid, and separately titrated 25.0 mL of a 0.100 mol L–1 strong
monoprotic acid.
15 Which statement about the volume of base required to reach the equivalence point is
correct?
(A) The weak acid will require the same volume of base as the strong acid.
(B) The weak acid will require a larger volume of base than the strong acid.
(C) The weak acid will require a smaller volume of base than the strong acid.
(D) The volume of base required will depend on the molar mass of the acid used

The answer is A but I don't understand how. Shouldn't it be C since there aren't as many H+ ions to react?

 

[Queenroot]

yeah that's weird. I guess in reality the weak acid will eventually go to completion and fully ionise, maybe that's why the answer is A.

 

[wowsugoi]

For a weak acid:

HA (aq) + H2O (l) <-> A- (aq) + H3O+ (aq)

In a titration, the base will neutralise with the newly formed hydronium ion. This shifts the equilibrium right in order to minimise the disturbance in the system.

Na(OH) (aq) + H3O+ (aq) -> Na+ (aq) + 2H2O (aq)

As the titration approaches the neutralisation point, the weak acid will completely ionise.

Since the concentration and volume of both the weak and strong acid are the same, they will both ionise to the same degree.

Hope this helps.