Equivalence point

[SaintJude]

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EDIT: Ah, never mind. I get it.

At the equivalence point, which of the following is true?
A. the concentration of acid is equal to the concentration of base.

B. the number of moles of base is equal to the original number of moles of acid present.

C. the [acid] is equal [conjugation acid] of the base added.

D. the number of moles of acid is equal to exactly half the total number of moles of dissolved species.


Highlight here for answer: Answer is B.

 

[chiddler]

can you explain why B is right and C is wrong. Also, how can D be changed to be true? (ie would it be true if it was a third instead of half?)

 

[SaintJude]

For choice D.) the moles of dissolved species could = moles of titrant + moles of acid ( and perhaps even other spectator ions!) So, I don't think D can ever apply to a point in a titration curve.

I'm not sure about Choice C. But I think it's wrong because it is describing a situation far from the equilibrium. I dare say it would never occur...Say you were titrating HCl with NH3. Choice C is saying [HCl]=[NH4+]. or [Cl-]=[NH3]

Sorry, don't have a better answer. I just memorized the def. of the equivalence point.