How to tell what fact to use to answer question?

[Sammy1024]

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I was doing this question just now:

48. Adding acid to an aqueous solution containing a basic salt has what effect?

A . It will increase the solubility.
B. It will decrease the solubility.
C . It will have no effect on the solubility.
D. It will lower the temperature of the solution.

I was down to A or B, and then I thought well adding more solutes to a solution would make the solubility decrease, but the answer key said that the acid and base would react freeing up more "space" leading to an increase in solubility.

I was wondering there were any suggestions for how to figure out which fact to use to answer a question because both make sense? Maybe i'm just wrong in my logic??

 

[blackmi4]

Adding solutes to a solution resulting in decreased solubility isn't a fact, so it shouldn't be used.

Every base has a solubility (g/L) based on the solvent it is put in. That is, there is a maximum amount of grams of the base that will dissolve in a given solvent.

You know that bases grab protons. After the maximum amount of base has dissolved in water (broken apart/grabbed enough protons of the water molecules), it stops dissolving.

If you add acid then not only are you changing the solvent (different solubility), you are adding more of what a base wants (protons).

You are adding more things on the left side of the equation. By L's principle, the reaction will go to the right.