Question

I am studying for ACS and have trouble understanding how to rank molecules in decreasing or increasing solubility in water...

I know the rules of which molecules are insoluable...But how do you rank them in which is least or most soluble.

The question in the acs included
In which set are the substances arranged in order of decreasing solubility in water?

(A) Al(OH)3 > Mg(OH)2 > NaOH

(B) BaSO4 > CaSO4 > MgSO4

(C) CaCO3 > NaHCO3 > Na2CO3

(D) AgCl > AgBr > AgI

Answer 1

there isn't straight forward to know the solubility of ionic compounds... you can use the size of the ions to a degree.

The best (and only real way without numerical values) is to know the solubility tables of these common ions and point out inconsistencies in the options. That eliminates A) and C)

From there we can use the size of the ions, the larger the ion (e.g. \(I^- ~vs~ F^-\)) the less soluble a compound will be - this has to do with the solvation spheres and enthalpy.

so i think the only one is D)

Answer 2

you could look at this for some insight https://en.wikipedia.org/wiki/Solubility_table

Answer 3

Yah, the answer is D. I just had trouble understanding why it is.

Answer 4

I remember it had something to do with polarity? is that true?

Answer 5

sure it does, but i think it's more accurately explained by solvation. water molecules have completely envelop the ions and shield their charge sufficiently in order to solvate (dissolve) them, the larger the ion (ionic radius), the more water molecules necessary.

there's tons of literature on this, you can look it up on google

Answer 6

ok thanks!

Answer 7

no problem!