March 28, 2024, 07:53:08 PM
Forum Rules: Read This Before Posting


Topic: Acids and Bases: how do I predict whether reactants or products will dominate  (Read 6246 times)

0 Members and 1 Guest are viewing this topic.

Byrne

  • Guest
In the following reaction, how do I predict whether the reactants and products will predominate at 25 degrees Celcius?

(i) HCO3- + HS- <-> H2CO3 + S2-

(ii) C2H3O2- + HNO2 <-> HC2H3O2 + NO2-
« Last Edit: December 20, 2005, 05:13:48 AM by Mitch »

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27633
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re:Acids and Bases...
« Reply #1 on: December 17, 2005, 07:11:20 PM »
Stronger acid protonates conjugated base of the weaker acid.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Byrne

  • Guest
Re:Acids and Bases...
« Reply #2 on: December 18, 2005, 12:25:32 AM »
'protonates?'

I don't think I've ever heard that term before, but I'm assuming it means the stronger acid donates a proton to the conjugate base of the weaker acid.  I still don't understand how this helps me determine whether the reactants or products will dominate.

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27633
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re:Acids and Bases...
« Reply #3 on: December 18, 2005, 05:20:10 AM »
In other words - stronger acid will be dissociated, weaker will be not.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline Donaldson Tan

  • Editor, New Asia Republic
  • Retired Staff
  • Sr. Member
  • *
  • Posts: 3177
  • Mole Snacks: +261/-13
  • Gender: Male
    • New Asia Republic
Re:Acids and Bases...
« Reply #4 on: December 18, 2005, 08:22:10 AM »
(i) HCO3- + HS- <-> H2CO3 + S2-

Which is the stronger acid? bicarbonate or hydrogen sulphite?

since carbonate anion is a stronger base than the sulphite anion, then HS- must be a stronger acid than HCO3-, therefore the bicarbonate anion will be protonated.

Try to follow this line of reasoning for the 2nd reaction..
« Last Edit: December 18, 2005, 08:22:51 AM by geodome »
"Say you're in a [chemical] plant and there's a snake on the floor. What are you going to do? Call a consultant? Get a meeting together to talk about which color is the snake? Employees should do one thing: walk over there and you step on the friggin� snake." - Jean-Pierre Garnier, CEO of Glaxosmithkline, June 2006

Byrne

  • Guest
Re:Acids and Bases...
« Reply #5 on: December 18, 2005, 04:19:10 PM »
Okay, I think I understand how to determine which side the reaction favors if you know which acid is stronger, but how do you determine that?  Normally we are given the KA value, so it's easier to determine which is the stronger acid.

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27633
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re:Acids and Bases...
« Reply #6 on: December 18, 2005, 04:51:25 PM »
And if you are not given their values you are hopelessly lost? There are tons of books, links, sites with these values. Check on the left or follow Ka and Kb link, or visit google.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Sponsored Links