Register to reply

Distributions within saturated solutions

by JeffEvarts
Tags: distributions, saturated, solutions
Share this thread:
JeffEvarts
#1
Apr13-14, 05:57 PM
P: 34
There are some really really good treatises out there on fractional crystallization, and I'm ploughing through them one at a time.

One very basic thing has me confused, though: If you have 1 liter of water at 100C, it will dissolve 455g of NaCO3 or 1150 of KCO3, or pretty much any linear combination of those two. (The saturation curve is definitely nonlinear at lower temperatures, but that's not important for this question.)

Suppose I
1) put 1.5kg of each in a single flask,
2) intermix them carefully
3) add a liter of water
4) raise the combined temp to 100 degrees
5) let the system stabilize
6) draw off 100ml of clear fluid

Am I going to get
1) A saturated solution containing ONLY the most soluble salt
2) A combination of salts based on available amounts (50/50)
3) a mixture based on something else (temperature? atomic weight?)

Thanks for your time,
-Jeff Evarts
Phys.Org News Partner Chemistry news on Phys.org
Faster, cheaper tests for sickle cell disease
Simulations for better transparent oxide layers
Characterizing strontium ruthenate crystals for electrochemical applications
Chestermiller
#2
Apr13-14, 08:46 PM
Sci Advisor
HW Helper
Thanks
PF Gold
Chestermiller's Avatar
P: 5,259
Have you learned about the concept of solubility product yet?

Chet
JeffEvarts
#3
Apr14-14, 06:35 AM
P: 34
ChesterMiller: Yes, at least the basics.

The solubility product is an equilibrium expression (like SO2/O2 vs SO3 in gasses) that tells us how much of a single salt will be solvated when a system of that salt and water stabilizes.

It is my current (limited) understanding that there is cross-inhibition between salts, that is: If a solution is saturated with (say) NaOH, then less CaOH will enter solution than if there was no NaOH. It is about this that I am asking: If there's enough to saturate either way, how do I determine what the solution will contain?

-Jeff

Chestermiller
#4
Apr14-14, 09:41 AM
Sci Advisor
HW Helper
Thanks
PF Gold
Chestermiller's Avatar
P: 5,259
Distributions within saturated solutions

Hi Jeff,

If you know how much NaCO3 and how much KCO3 dissolve in isolation, then you know the solubility product for each. When you dissolve both at the same time, you must satisfy the solubility products for both of them simultaneously. Let x be the amount of KCO3 that dissolves, and y be the amount of NaCO3 that dissolves. CO3 is common to both so there will be x + y CO3 formed. This gives you two equations and two unknowns (the two solubility product equations) to solve for x and y. (If you divide one equation by the other, you immediately have the ratio of x to y).

Chet
JeffEvarts
#5
Apr14-14, 10:07 AM
P: 34
LOL. I tend to oversimplify things, but in this case I overcomplicated them.

Thank you Chet
Borek
#6
Apr14-14, 11:28 AM
Admin
Borek's Avatar
P: 23,597
Just remember in such concentrated solutions calculations are quite difficult, because of the very high ionic strength.
Chestermiller
#7
Apr14-14, 09:27 PM
Sci Advisor
HW Helper
Thanks
PF Gold
Chestermiller's Avatar
P: 5,259
Quote Quote by Borek View Post
Just remember in such concentrated solutions calculations are quite difficult, because of the very high ionic strength.
Yes. You need to use an appropriate activity coefficient model, often an extended version of Debye Huckel. See Handbook of Aqueous Electrolyte Thermodynamics: Theory & Application by Joseph F. Zemaitis Jr., Diane M. Clark, Marshall Rafal and Noel C. Scrivner

Chet


Register to reply

Related Discussions
Approximating distributions with other distributions Calculus & Beyond Homework 4
Ksp, saturated solutions and precipitation (Ionic Equilibria) Chemistry 1
Dilute, Unsaturated, Saturated and Supersaturated solutions Biology, Chemistry & Other Homework 2
Mixture of saturated liquid and saturated vapor Biology, Chemistry & Other Homework 3
BPS Saturated? Beyond the Standard Model 2