March 29, 2024, 10:28:27 AM
Forum Rules: Read This Before Posting


Topic: Mass Balance Equations  (Read 12532 times)

0 Members and 1 Guest are viewing this topic.

Offline FAC208aussie

  • New Member
  • **
  • Posts: 3
  • Mole Snacks: +0/-0
Mass Balance Equations
« on: September 10, 2009, 12:30:19 AM »
I am having trouble comprehending the mass-balance eqn.
.25 M in NaF and saturated with CaF2
Would my eqn then be:

.25 M = Na+ = F- + CaF2

both of those are in concentraitons.

Offline poca

  • Regular Member
  • ***
  • Posts: 17
  • Mole Snacks: +0/-0
Re: Mass Balance Equations
« Reply #1 on: October 01, 2011, 09:26:48 PM »
*Ignore me, I am impatient*, I am working on this exact problem

If CaF2, is not soluble how do you include it in the equation?

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27635
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Mass Balance Equations
« Reply #2 on: October 02, 2011, 05:44:57 AM »
Please elaborate on what the question is, as it looks ambiguous.

Mass balance of what? There are several mass balance equations for this system, some are not important, at least one is necessary to find the equilibrium.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline poca

  • Regular Member
  • ***
  • Posts: 17
  • Mole Snacks: +0/-0
Re: Mass Balance Equations
« Reply #3 on: October 02, 2011, 08:09:09 AM »
The question is, Write the mass balance expressions for a solution that is.
.25M NaF and saturated with CaF2

.25M = [Na+]
.25M = [F-]+

I should mention I'm very lost on how to do these problems...

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27635
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Mass Balance Equations
« Reply #4 on: October 02, 2011, 01:53:15 PM »
OK.

You are right about sodium, however, you are wrong about fluorides. Where do they come from?

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

Offline poca

  • Regular Member
  • ***
  • Posts: 17
  • Mole Snacks: +0/-0
Re: Mass Balance Equations
« Reply #5 on: October 02, 2011, 04:32:48 PM »
.25M F from NaF, but CaF2 is solid, i guess if it dissolves then excess of CaF2, how much does that contribute
.25M= [F-] + [F-]2

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27635
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Mass Balance Equations
« Reply #6 on: October 02, 2011, 05:02:10 PM »
You never square anything in mass balances, you just use stoichiometric coefficients.

There are two sources of fluorides - sodium fluoride and dissolved calcium fluoride. Can you express concentration of fluorides in terms of concentrations of sodium and calcium?
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline poca

  • Regular Member
  • ***
  • Posts: 17
  • Mole Snacks: +0/-0
Re: Mass Balance Equations
« Reply #7 on: October 02, 2011, 05:33:19 PM »
[Na] = [F] = .25M
2[Ca] = [F] = ?

Offline poca

  • Regular Member
  • ***
  • Posts: 17
  • Mole Snacks: +0/-0
Re: Mass Balance Equations
« Reply #8 on: October 02, 2011, 09:36:28 PM »
[F-] = [Na] + 2[Ca]

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27635
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Mass Balance Equations
« Reply #9 on: October 03, 2011, 05:08:55 AM »
[F-] = [Na] + 2[Ca]

And that's correct.

You already wrote another one earlier - describing concentration of Na+.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline luke1987

  • Very New Member
  • *
  • Posts: 1
  • Mole Snacks: +0/-0
Re: Mass Balance Equations
« Reply #10 on: November 15, 2012, 03:31:41 PM »
Why wouldn't FAC's original equation be correct? I don't understand why you would set concentrations equal to [F-], since there are two sources...wouldn't you set equal to [Na+] because there is only one source?

Sponsored Links