February 27, 2021, 01:55:20 AM
Forum Rules: Read This Before Posting


Topic: Finding concentration of H2O2 by redox titration.  (Read 26096 times)

0 Members and 1 Guest are viewing this topic.

Offline upsidedown

  • Regular Member
  • ***
  • Posts: 30
  • Mole Snacks: +0/-0
Finding concentration of H2O2 by redox titration.
« on: April 24, 2009, 04:09:56 PM »
I writting a plan on how to determine the concentraion of hydrogen peroxide, H2O2, by a redox titration with potassium mangante (VII), K2MnO4.
The solution of hydrogen peroxide is know to be approximately 100-volume.
I know that I should start by diluting the H2O2, but im not sure what to do after to find the exact concentraion of H2O2.

The equation ifor this is:
5H2O2 + 2KMnO4 + 3H2SO4  ----> 2MnSO4 + K2SO4 + 5O2+ 8H2O         

Thanks for any help.

Offline plankk

  • Full Member
  • ****
  • Posts: 150
  • Mole Snacks: +20/-4
  • Gender: Female
Re: Finding concentration of H2O2 by redox titration.
« Reply #1 on: April 24, 2009, 04:32:13 PM »
Then you should acidize your solution of H2O2. The next step is doing the titration by using the solution of KMnO4 of known concentration. After all you have to calculate how much H2O2 you have by using the reaction's equation.

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 26302
  • Mole Snacks: +1710/-402
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Finding concentration of H2O2 by redox titration.
« Reply #2 on: April 24, 2009, 05:48:59 PM »
Final calculations won't be different from any other titration.

http://www.titrations.info/titration-calculation
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline upsidedown

  • Regular Member
  • ***
  • Posts: 30
  • Mole Snacks: +0/-0
Re: Finding concentration of H2O2 by redox titration.
« Reply #3 on: April 25, 2009, 08:21:40 AM »
I know I have to used acidified KmnO4,
do a acidify it just by adding H2SO4, and will this effect the concentration of KmnO4?

Offline UG

  • Full Member
  • ****
  • Posts: 822
  • Mole Snacks: +134/-15
  • Gender: Male
Re: Finding concentration of H2O2 by redox titration.
« Reply #4 on: April 25, 2009, 08:54:28 AM »
Should be no problem.

Offline plankk

  • Full Member
  • ****
  • Posts: 150
  • Mole Snacks: +20/-4
  • Gender: Female
Re: Finding concentration of H2O2 by redox titration.
« Reply #5 on: April 25, 2009, 09:04:53 AM »
If you add the solution of H2SO4 to the solution of KMnO4, the concentration of KMnO4 of course changes (the volume grows). If you do in this way your calculation will be harder and titration could be done with bigger measuring error. The better idea is to acidify the solution of hydrogen peroxide. Then it isn't important how diluted is your solution. From calculation you will find a n (the number of moles H2O2). And to find concentration of your solution (which you dilute in the first step), you have to know how volume you take for titration.

Offline upsidedown

  • Regular Member
  • ***
  • Posts: 30
  • Mole Snacks: +0/-0
Re: Finding concentration of H2O2 by redox titration.
« Reply #6 on: April 25, 2009, 09:11:36 AM »
How much H2SO4 should I add?

Does it decrease the concentraion the same as just adding distilled water?

Thanks for the help.

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 26302
  • Mole Snacks: +1710/-402
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Finding concentration of H2O2 by redox titration.
« Reply #7 on: April 25, 2009, 03:25:19 PM »
You should take aliquot of hydrogen peroxide solution, add sulfuric acid, titrate with pemanganate. Note, that amount of hydrogen peroxide after the aliquot was taken doesn't change - concentration does, but number of moles is constant. Thus changes in concentration can be safely ignored.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline upsidedown

  • Regular Member
  • ***
  • Posts: 30
  • Mole Snacks: +0/-0
Re: Finding concentration of H2O2 by redox titration.
« Reply #8 on: April 26, 2009, 05:38:20 AM »
You should take aliquot of hydrogen peroxide solution, add sulfuric acid, titrate with pemanganate. Note, that amount of hydrogen peroxide after the aliquot was taken doesn't change - concentration does, but number of moles is constant. Thus changes in concentration can be safely ignored.

Im not sure what you mean, if water is added the concentraion changes, but if H2SO4 is added it does not?


Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 26302
  • Mole Snacks: +1710/-402
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Finding concentration of H2O2 by redox titration.
« Reply #9 on: April 26, 2009, 05:44:10 AM »
Concentration changes in both cases, but it doesn't matter, as the amount of the substance titrated is the same.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline upsidedown

  • Regular Member
  • ***
  • Posts: 30
  • Mole Snacks: +0/-0
Re: Finding concentration of H2O2 by redox titration.
« Reply #10 on: April 26, 2009, 06:03:02 AM »
So if 25cm3 of 0.02 mol dm -3 Potassium manganate was needed titrate against H2O2
You work you work out the concentraion of H2O2 the same no matter how diluted it is?

Also, how much sulfuric acid would be enough to acidify H2O2?

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 26302
  • Mole Snacks: +1710/-402
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Finding concentration of H2O2 by redox titration.
« Reply #11 on: April 26, 2009, 07:00:21 AM »
You don't calculate concentration of H2O2 in the titrated solution. Instead, you calculate number of moles of H2O2 titrated, and as you know volume of aliquot of hydrogen peroxide taken, you can calculate concentration in the ORIGINAL sample. So yes, dilution of your aliquot doesn't matter, as it doesn't change number of moles of H2O2.

Also, how much sulfuric acid would be enough to acidify H2O2?

Recipe from my book: put solution containing 40-70 mg H2O2 into 500 mL flask. Dilute to 200 mL, add 20 mL 30% H2SO4, titrate with 0.1n permanganate.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline upsidedown

  • Regular Member
  • ***
  • Posts: 30
  • Mole Snacks: +0/-0
Re: Finding concentration of H2O2 by redox titration.
« Reply #12 on: April 26, 2009, 07:21:19 AM »
If I calculate moles of Potassium Manganate by : volume (cm3) × concentration
                                                                                    1000

Then work out the moles of H2O2 by the 5:2 ratio.

Then calculate concentraion by: =                  moles                   
                                                         (volume (cm3) / 1000)

Would this give me the concentraion of H2O2 in my orginal solution?

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 26302
  • Mole Snacks: +1710/-402
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Finding concentration of H2O2 by redox titration.
« Reply #13 on: April 26, 2009, 08:04:32 AM »
Looks OK. That's assuming you used correct volume in the second part of your calculations.

Note:

If I calculate moles of Potassium Manganate

PERmanganate.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline upsidedown

  • Regular Member
  • ***
  • Posts: 30
  • Mole Snacks: +0/-0
Re: Finding concentration of H2O2 by redox titration.
« Reply #14 on: April 26, 2009, 08:17:00 AM »
Would I need to calculate the moles of permanganate ?

Sponsored Links