March 28, 2024, 08:50:56 AM
Forum Rules: Read This Before Posting


Topic: Redox half-reaction in an acidic solution.  (Read 2980 times)

0 Members and 1 Guest are viewing this topic.

Offline bopll

  • Very New Member
  • *
  • Posts: 2
  • Mole Snacks: +0/-0
Redox half-reaction in an acidic solution.
« on: September 29, 2010, 06:45:37 PM »
The problem: complete the half reaction.

C2O42-  :rarrow: CO2 (acidic solution)

the answer manual gives the following:

H2C2O4  :rarrow: 2 CO2 + 2 H+ + 2 e-

that's dandy and all, but why on earth did the hydrogens bond to the C2O42- instead of just floating around like in the following reaction?

6 e- + 14 H+ + Cr2O72-  :rarrow: 2 Cr3+ + 7 H2O

the methodology in the second one makes sense to me, but not the first one.  what's the difference in the two? They're done in two completely different ways.  And each different way produces a different answer.  

thanks

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27637
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Redox half-reaction in an acidic solution.
« Reply #1 on: September 29, 2010, 06:57:59 PM »
Oxalic acid is a weak one.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline bopll

  • Very New Member
  • *
  • Posts: 2
  • Mole Snacks: +0/-0
Re: Redox half-reaction in an acidic solution.
« Reply #2 on: September 29, 2010, 08:03:15 PM »
Isn't chromic acid a weak acid too?

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27637
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Redox half-reaction in an acidic solution.
« Reply #3 on: September 30, 2010, 02:51:14 AM »
Good question. As far as I remember it is much stronger one.

Perhaps it is just a matter of convention then. I have no problems with writing oxalate oxidation equation in both forms (as oxalate and as an acid). As it is usually oxidized in very low pH it is mostly protonated, so the situation is relatively simple. With chromic acid it is much more complicated - it gets protonated to some extent, but it also polymerizes (dichromate is only a first step).
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Sponsored Links