Question

Where does the equivalence point occur on a titration curve for a strong acid-strong base titration?
[A] At the end point, after pH=7.
[B] At pH=7 in the middle of the dramatic slope.
[C] At the very end of the titration at pH 10-12.
[D] Before the slope increases dramatically, between pH 2 and 4.

Answer 1

Hint: For a strong acid and a strong base titration, equal moles of both the ions are present at the equivalence point. The equivalence point lies at a neutral point for this titration.

Complete answer:
As we know, a titration curve gives us the idea of the pH of a solution throughout the titration in a graphical form.
When we conduct a titration, we keep adding the titrant to the given solution until the colour changes. The colour change depicts that the titration is over.
Generally in a titration, we take an acid and a base either strong or weak. This gives us four types of titration: strong acid + strong base, strong acid + weak base, weak acid + strong base and weak acid +weak base titration. The pH of the solution changes differently for each type throughout the titration, which gives us a different curve for each of them.
Generally, a titration curve represents the change in pH of the solution. In the question, we are asked about the titration curve of a strong acid + strong base.
Equivalence point is the point where the number of moles of acid is equal to the number of moles of base. Equivalence point is also different depending on the strength of the acid and base.
As both acid and base are strong, it means both of them will dissociate equally to gives us equal moles of ${{H}^{+}}\text{ and O}{{\text{H}}^{-}}$ i.e. when the acid is completely neutralised by the base, solution is neutral and that point is the equivalent point too. Therefore, for a strong acid + strong base titration, the equivalence is at pH 7.
The titration curve for this titration looks like-

At pH=7, the ${{H}^{+}}$ ions are completely neutralised by the $O{{H}^{-}}$ ions.

Therefore, the correct answer is option [B] at pH=7 in the middle of the dramatic slope.

Note:
The equivalence point for a strong acid + weak base is at a lower pH and the solution is acidic whereas for a weak acid + strong base, the equivalence point is reached at a higher pH thus the solution is acidic. For a strong acid and strong base, the solution is neutral.