March 29, 2024, 12:47:18 AM
Forum Rules: Read This Before Posting


Topic: How to back titrate this hypothetical soln  (Read 2677 times)

0 Members and 1 Guest are viewing this topic.

Offline johnnyjohn993123

  • Regular Member
  • ***
  • Posts: 57
  • Mole Snacks: +0/-0
How to back titrate this hypothetical soln
« on: January 16, 2016, 08:41:49 PM »
How to back titrate this hypothetical soln?
How can I back titrate my hypothetical solution whose 2.50ml of 0.1M of HCl created a fuchsia pink in my soln and when I placed 1.30ml of 0.08M of NaOH my soln turned colorless..and when I added 2.40ml of 0.1 HCl my soln turned pale pink. How to go with my added NaOH here? Whats the real volume of my HCl to reach my end point?  I didnt know about this coz I was absent when this was taught.

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27633
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: How to back titrate this hypothetical soln
« Reply #1 on: January 17, 2016, 03:12:55 AM »
Please elaborate, it is not entirely clear what you did and why you want to do back titration (instead of a normal titration). What is the aim of the exercise?

Also: what was the indicator?

See if this page doesn't help: http://www.titrations.info
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline Arkcon

  • Retired Staff
  • Sr. Member
  • *
  • Posts: 7367
  • Mole Snacks: +533/-147
Re: How to back titrate this hypothetical soln
« Reply #2 on: January 17, 2016, 06:44:45 AM »
If you started with a colorless solution of some volume and some unknown molarity of HCl, and the typical indicator phenolpthalein, and you titrated with a known volume and molarity of NaOH to the appearance of a pink endpoint, you'd know exactly what the endpoint was, and what calculations to do.

I just wrote that to let you know the assumptions we have to make, because you weren't as clear.

If you've overshot with the NaOH, and can't just start over, then you can add a known volume of more HCl, until clear, and titrate again to the endpoint.  In which case, its as if you simply started with more HCl solution -- the sum of your two solutions.

Are you doing something like that?
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline johnnyjohn993123

  • Regular Member
  • ***
  • Posts: 57
  • Mole Snacks: +0/-0
Re: How to back titrate this hypothetical soln
« Reply #3 on: January 17, 2016, 10:37:43 AM »
If you started with a colorless solution of some volume and some unknown molarity of HCl, and the typical indicator phenolpthalein, and you titrated with a known volume and molarity of NaOH to the appearance of a pink endpoint, you'd know exactly what the endpoint was, and what calculations to do.

I just wrote that to let you know the assumptions we have to make, because you weren't as clear.

If you've overshot with the NaOH, and can't just start over, then you can add a known volume of more HCl, until clear, and titrate again to the endpoint.  In which case, its as if you simply started with more HCl solution -- the sum of your two solutions.

Are you doing something like that?


Exactly Paragraph 3... yes.. how can I calculate the volume of a know  conc of NaOH that reacted with the analyt given that I have used a back titrant. I just wanna see how the number works here. Thats why I've set a theoretical example.

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27633
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: How to back titrate this hypothetical soln
« Reply #4 on: January 17, 2016, 12:23:36 PM »
It is just about tracking stoichiometry.

http://www.titrations.info/back-titration

Your example looks a bit suspicious, as you suggest starting with acid and fuchsia color, then titrating it with NaOH till the color is lost. Well, the indicator that changes from colorless to fuchsia is phenolphthalein, but it changes color in exactly reverse way - it is colorless in low pH, and becomes pink in a high one.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Sponsored Links