Why is $\ce{[HIn] = [In-]}$ at equivalence point of a titration? I know that at equivalence point moles of known solution is equal to the moles of unknown solution, but I'm not able to relate that fact with the above conclusion. Perhaps I'm don't know something.

  • $\begingroup$ @Shuvam at equivalence point the reductant and oxidant are equal in their mole stoichiometric. $\endgroup$
    – JM97
    Commented Aug 27, 2016 at 9:37
  • $\begingroup$ @Shuvam hope this helps chemguide.co.uk/physical/acidbaseeqia/indicators.html $\endgroup$
    – JM97
    Commented Aug 27, 2016 at 9:56
  • $\begingroup$ What is $\mathrm{HIn}$? The indicator? If so, this statement is false. The equivalence point is by definition when you have added a stoichiometric amount of the titrant to the analyte. $\endgroup$
    – Zhe
    Commented Oct 27, 2016 at 17:35

2 Answers 2


Ideally, the concentration of indicator is much, much lower than the concentration of the material to be titrated and of that used to titrate. Therefore, less than a drop of standard solution is needed to make the indicator entirely cross the equivalent point.

For most titrations, the equivalence point of the indicator is not the end point. It’s just somewhere near. And the only thing you can actually see and record is said indicator’s colour change. So it’s the only thing you can resort to.

The important choice in a titration is choosing the correct indicator. If you are titrating a strong acid with a strong base (so the titration’s equivalence point is approximately $7$), you want an indicator whose equivalence point is just behind that (at ca. $8$), so that the tiniest of drops added additionally will cause the colour change.


As you might already know, $\ce{[In^-]}$ is the concentration of the indicator that was added to the solution, which basically shows whether the solution is basic or acidic or neutral. The equivalence point of a titration is when the titrant has reacted with the unknown chemical solution so that it reaches an endpoint of the indicator. The equalization of the concentration $\ce{[HIn] = [In^-]}$ is when the color is at its neutral state: neither colors of the indicator is dominant over the other.

  • 2
    $\begingroup$ I have downvoted this answer because it is not true that the equivalence point of a titration is when a solution is neutral; consider the titration of a weak base with a strong acid, for example. The equivalence point of a titration occurs when all the titrant has reacted. $\endgroup$ Commented Aug 28, 2016 at 3:44
  • $\begingroup$ Oh, right. Stupid mistake. I do believe the rest of the answer should be right though. Is it? $\endgroup$
    – phi2k
    Commented Aug 28, 2016 at 14:41
  • $\begingroup$ Yes, I believe so. $\endgroup$ Commented Aug 28, 2016 at 19:21

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.