Altius 3 C/P #7

[salemstein]

I don't get how C is the answer. If you dissolve both CaF2 and CaSiO3 in water, won't the Ca2+ be the same as SiO3 due to common-ion effect?

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[theonlytycrane]

CaSiO3(s) -> Ca + SiO3

Any dissolution of CaF2 -> Ca + 2F makes more Ca than SiO3, even if the common-ion effect hinders additional dissolution due to the common Ca2+ ion.

 

[aldol16]

I don't get how C is the answer. If you dissolve both CaF2 and CaSiO3 in water, won't the Ca2+ be the same as SiO3 due to common-ion effect?

In a way, it will be > [SiO3] because of the common ion effect. So say 10 molecules of CaSiO3 would have dissolved to make 10 Ca and 10 SiO3. Well, now that you also have CaF2 in that system, say 4 molecules of CaF2 dissolve to give you 4 Ca and 8 F. So these 4 take the place of some of the 10 allowed from the CaSiO3 and so only 6 of the CaSiO3 can now be dissolved to give you 10 Ca total. It's a simplification, but think about it that way.