February 28, 2020, 05:52:23 PM
Forum Rules: Read This Before Posting


Topic: pH by the equivalence point  (Read 3693 times)

0 Members and 1 Guest are viewing this topic.

Offline Kritkatten

  • New Member
  • **
  • Posts: 4
  • Mole Snacks: +0/-0
pH by the equivalence point
« on: February 18, 2010, 11:13:21 AM »
Hello all! Nice to see a forum for chemistry! :)

I'm new here and a beginner in the awesome subject of chemistry. Glad to meet you all! Please excuse my eventual bad grammar/spelling, English is not my first language...

So, here's something I've tried to solve all day:

1.24 gram benzoic acid solution was diluted to 50.0 cm3. After shaking it, the solution was titrated with 0.180 M NaOH. What was the pH in the solution by the equivalence point?

So, I know that by the eq. point, the amount of mol acid should be equal to the amount of mol base, but that's about as far as I've got. :(

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 25518
  • Mole Snacks: +1671/-398
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: pH by the equivalence point
« Reply #1 on: February 18, 2010, 01:42:25 PM »
Benzoate is a weak base.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline cpncoop

  • Regular Member
  • ***
  • Posts: 95
  • Mole Snacks: +6/-3
Re: pH by the equivalence point
« Reply #2 on: February 18, 2010, 01:55:14 PM »
You may be overthinking this a bit.... pH is a measure of H+ concentration.  If the amount of H+ you have present (from benzoic acid) is neutralized by an equal amount of NaOH you have a neutral solution.... What is the pH of a neutral solution?

Offline Kritkatten

  • New Member
  • **
  • Posts: 4
  • Mole Snacks: +0/-0
Re: pH by the equivalence point
« Reply #3 on: February 18, 2010, 02:00:23 PM »
You may be overthinking this a bit.... pH is a measure of H+ concentration.  If the amount of H+ you have present (from benzoic acid) is neutralized by an equal amount of NaOH you have a neutral solution.... What is the pH of a neutral solution?

Well, the pH of a neutral solution is 7, right? But that is not the correct answer. The final solution will be basic.

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 25518
  • Mole Snacks: +1671/-398
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: pH by the equivalence point
« Reply #4 on: February 18, 2010, 06:16:43 PM »
I hate to repeat myself, but

The final solution will be basic

- because benzoate is a weak base.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline Kritkatten

  • New Member
  • **
  • Posts: 4
  • Mole Snacks: +0/-0
Re: pH by the equivalence point
« Reply #5 on: February 19, 2010, 03:04:17 AM »
I hate to repeat myself, but

The final solution will be basic

- because benzoate is a weak base.

Yes, thank you. That's how I know it'll be a basic solution. :) But I still don't know how to "start". I've written down the reaction, also calculated the concentration of the benzoate (0.02 M).
I'm new to these kind of equilibrium schemes. Don't know where to begin.  ???

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 25518
  • Mole Snacks: +1671/-398
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: pH by the equivalence point
« Reply #6 on: February 19, 2010, 04:16:22 AM »
Use Kb and concentration to calculate pOH.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Sponsored Links