Help With Past HSC Multiple Choice! (1 Viewer)

[MathsGirl]

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 cannot understand why, If someone could explain I would really appreciate

 

[kenkap]

i thought it was C...

 

[MathsGirl]

That's what I thought kenkap, but it's not !

 

[dawooddaman]

It A because both are monoprotic meaning same H ions will be released.

 

[7eleven]

It is A
If u replaced the NaOH with a weaker base, then it would be C

 

[MathsGirl]

I understand that they are monoprotic, but how would weak monoprotic release the same amount of H ion, as strong monoprotic.
Weak acids do not dissociate fully, so they release less ions, don't they ? This is where my confusion is.

 

[deswa1]

Think about it like Le Chat's principle. You are constantly removing the products of the reaction so equilibrium keeps shifting to the right -> therefore whether its a weak acid or a strong acid, they both essentially fully ionise under the titration. Therefore the volume is the same for both

 

[dawooddaman]

A monoprotic acid is an acid that donates only one proton or hydrogen atom per molecule to an aqueous solution. Doesn’t matter if it weak or strong only one proton can be accepted/received, thus equivalence point has to be the same.

 

[B3A13]

A monoprotic acid is an acid that donates only one proton or hydrogen atom per molecule to an aqueous solution. Doesn’t matter if it weak or strong only one proton can be accepted/received, thus equivalence point has to be the same.

+1

 

[MathsGirl]

Thanks guys for your help!! I kind of understand it