0
$\begingroup$

I created two graphs of two different titrations : One graph was the titration curve of acetic acid with sodium hydroxide (weak acid-strong base) and the other was that of nitric acid with sodium hydroxide (strong acid-strong base). I've marked the equivalence point of the acetic acid curve to be at a pH of ~8.5, while the nitric acid curve has a pH of 7.

Knowing this, where would I label the endpoint of the titration curves? In the same general location? On most of the photos I've researched, people don't tend to label the end point but it's required for this assignment. For the titration, I didn't use an color indicator like methyl red or anything but rather a pH meter. If anyone can give an idea, that would be greatly appreciated.

Improve this question
$\endgroup$

1 Answer 1

Reset to default
1
$\begingroup$

The endpoint and equivalence point are different.

According to this Wikipedia article , "The endpoint (related to, but not the same as the equivalence point) refers to the point at which the indicator changes colour in a colourimetric titration."

Essentially, the endpoint is when the titration visually ends in an experimental setting, but the equivalence point is when the titration actually ends, or when the moles of acid are equilalent to the moles of base.

Since you didn't use an indicator, you didn't have an endpoint.

Also, if you did use an indicator, you wouldn't really know what pH the titration ended at because you don't have a pH meter to measure the pH with.

Unless you had both a pH meter AND indicator (which seems kind of useless), you shouldn't have to label the endpoint on any titration curve.

Improve this answer
$\endgroup$
5
  • $\begingroup$ I did use a pH meter. I recorded the amount of NaOH added in 1-2 mL increments to see the change in pH until it reached the equivalence point. Would the end point be the moment in which a huge spike was seen? For instance, in the nitric acid, the pH meter read 3.4 to 10.8 from 13 mL to 14 mL added. Would this be it? Thanks! $\endgroup$
    – user55614
    May 1, 2018 at 23:41
  • $\begingroup$ There is no endpoint. The endpoint is when the indicator changes color, but you didn't have an indicator. $\endgroup$
    – Frank
    May 1, 2018 at 23:44
  • $\begingroup$ There's still an end pont. The end point is the end of the titration. You waited until pH>7 to stop. But you didn't stop at exactly pH = 7, the equivalence point. $\endgroup$
    – Zhe
    May 2, 2018 at 0:00
  • $\begingroup$ I wouldn't call that an endpoint. The endpoint is supposed to be near the equivalence point if anything. When plotting a titration curve with a pH meter, you usually overshoot the equivalence point by quite a bit so you can get data across the entire curve. I guess you could say that is the point where you ended, the literal ending point, but that isn't really a useful thing to measure. $\endgroup$
    – Frank
    May 2, 2018 at 0:04
  • $\begingroup$ @Frank It is definitely an endpoint. The equivalence point is when you the amounts are stoichiometrically equal. The end point is when your indicator, meter, etc. says that you're past the equivalence point, indicating that you have reached the end of the titration. Hence, "end point." See, for example: en.wikipedia.org/wiki/… $\endgroup$
    – Zhe
    Jul 1, 2018 at 21:06

Your Answer

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

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