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Author: Subject: A solubility question?
servo
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A solubility question?

Hey everyone,
A question has been roaming in my mind for sometime about solubility of two different compounds with similar solubility in same solvent like for example

Barium Chloride and Ammonium chloride both show somewhat similar solubility curve now my question is if i mix barium chloride and ammonium chloride in 1:1 ratio lets say 35 grams each and then dissolve them in 100 ml of water which will be soluble in water? both in 50 50 ratio or one will dissolve before and other will remain precipitated?
DraconicAcid
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They'll both dissolve to some degree, slightly lower than their normal solubility, due to the common ion effect.

If you want to talk about things that are very soluble (such as ammonium chloride), then you have to muck around with activity coefficients and ionic strength, so let's run through an example using compounds that are only slightly soluble. Since I can't be bothered to look up any real numbers, let's say MX and QX2, which both have a solubility of 0.0010 mol/L in water.

This means that MX has a Ksp of 1e-6, and QX2 has a Ksp of 4e-9. These are the equilibrium constants for the reactions:
MX(s) === M+(aq) + X-(aq)
QX2(s) === Q(2+)(aq) + 2 X-(aq)

If we toss both MX and QX2 into some water, both will dissolve. A quantity (m) of MX will go into solution, as will a quantity (q) of QX2.

This gives [M+] = m; [Q2+] = q, and [X-] = m + 2q.

We have two equations, m times (m + 2q) = 1e-6 and q times (m+2q)^2 = 4e-9, and we have two unknowns. Solve for them.

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yobbo II
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Look up mutual solubiliity of the compounds.
Or look up something like 'the system barium chloride, ammonium chloride, water.

Look it up in the solubility data series (a series of volumes produced over the years). The system may be in it.

If you obtain a mutual solubility diagram you will have to understant mutual solubility diagrams. Not the most exciting of subjects.

Janceck diagrams are the full story.