Question

How would you compare the relative solubilities of `BaCrO_4` and `BaCr_2O_7`?

Answer 1

We would tentatively assume that the dichromate is more soluble than the chromate.........

Explanation:

Generally dichromate salts are more soluble than the corresponding chromate salts. Why? Because the dichromate is larger than the chromate, and thus LESS charge dense, and should thus be LESS effectively solvated in an aqueous medium, and the ionic bond between cation and dianion should be weaker. Entropy and enthalpy would suggest that `BaCr_2O_7` is the more soluble. I have no data to support this argument (I could not find the solubilities on the web), and you need such data as a physical scientist.