[yus]

Hello all,

I have a question regarding the solubility in the quaternary system of NaCl-MgCl2-KCl-H2O.
I am trying to understand why in a lot of scenarios, the nacl or kcl is unsaturated.
for example, in 0.25 L of pure water, i added 80g of nacl, 12g of mgcl2 and 10g of kcl, mixing for 2 hours around 24.5 degC. In the end, only 65.3g of nacl, 9.88g mgcl2 and 8.08g kcl dissolved. S.G. is 1.211 and mass% of nacl is 21.58%, mgcl2 is 3.26% and kcl is 2.67%, but if we look at nacl and kcl, neither are saturated and the solution cannot dissolve more solids, why is this?
And when i test for chlorine, there is extra in the solution, is it just because of ions in the solution?

[Borek]

if we look at nacl and kcl, neither are saturated

Not sure what you are asking nor where you got this information from.

Do you know what is a common ion effect?

[jeffmoonchop]

I think you mean that they are saturated. The best way to get a saturated solution is to stir in excess, filter away the solid. The solution remaining is saturated.

If you have researched the solubility of each, and are trying to dissolve them all at that concentration, it may not work for a few reasons:

1. The solubility of NaCl in pure water may be different from the solubility of NaCl in a saturated KCl solution
2. The volume of water you use may be less than the volume required to dissolve the solids.
3. Following from that, water will evaporate in a couple of hours at 25C, especially when agitated, this means it will dissolve less.
4. Dissolution is often endothermic, so the water may need more time to equilibrate to 25C
5. The agitation is too low, try sonication

[yus]

Thank you all for your answer.

Let me just clarify a bit more.

I am working at a salt(nacl) production facility (solution mining) and in our brine, we have caso4, nacl, mgcl2 and kcl.
My question is that with mass% 3.15%mgcl2, caso4 0.32%, kcl 2.63% and nacl 20.78%, is this nacl being saturated?
Based on a software, this nacl is unsaturated in the solution. is this a correct statement?

I did a experiment myself (information given in the original post), the solution wont be able to dissolve more, but why?

Thanks again.

[Borek]

the solution wont be able to dissolve more, but why?

I hate to repeat myself, but do you know what is a common ion effect?

Do you know what is a solubility product, how it is defined and how it describes dissolution equilibria?

[yus]

Hi Borek,

Yes, i do know common ion effect.
The common ion here is cl-.

And i do know solubility product Ksp and its dissolution equilibrium.

[Borek]

So why are you surprised solubility of NaCl in the presence of other dissolved chlorides is lower?

[yus]

Hi Borek,

I am not surprised that NaCl is lower, i am surprised that when i compare my data with the data generated from software, my data is lower than the ones in software under the same condition. And i would love to know why?
Thats why i presented my data and asking if nacl is saturated?

Thanks again.

[Borek]

the ones in software

And how do you expect us to know what you mean by "data from software"?

[yus]

Hi Borek,

The software is called syscad and the saturation values are calculated based on D'an's (I am not sure what this is and i cannot find any information online).

I wonder if i could use solubility production to calcuate nacl saturation value in water when the amount of kcl and mgcl2 dissolved in water are given.

Thanks again.
sorry for the confusion.

[Borek]

Just browsing the SysCAD documentation produced this paper: d'Ans J. 1952 Die Bedeutung von Van' Hoff's Arbeiten Uber Losungsgleich-gewichte. Zeitschr. Electrochem.

[yus]

Thanks for all your help Borek!