Solubility Test: Equal Moles or Equal Mass?

[justadream]

---

Members do not see this ad.

Let's say I wish to test whether substance_X or substance_Y is more soluble in water.

The molecular weight of the two substances differs.

Should I add equal mass amounts of the substances into water (e.g., 5 grams of substance_X in 1L water, 5 grams of substance_Y in a separate 1L water beaker)?

Or, should I add equal molar amounts (e.g., 1 mol substance_X in 1L water, 1 mol of substance_Y in a separate 1L water beaker)?

 

[justadream]

To answer my own question:

I think it should be equal masses? Because otherwise, you'd have differing amounts of London dispersion forces?