1. The problem statement, all variables and given/known data Of the following solutions, the solubility of calcium hydroxide (s) is least in: 1) 0.4 M calcium chloride 2) 0.2 M barium hydroxide 3) 0.25 M calcium nitrate 4) 0.3 M potassium hydroxide 5) 0.45 M sodium nitrate 2. Relevant equations Either I haven't gotten to the relevant lecture yet or the prof just doesn't cover this topic in lecture. Either way, I found a U. Texas lecture online explaining that for the solubility of magnesium hydroxide, it is highest in a solution of hydrochloric acid as opposed to pure water, sodium hydroxide, or magnesium chloride, since the acidic hydrochloric acid will neutralize the hydroxide in the metal hydroxide, allowing more to dissolve. 3. The attempt at a solution So by the above logic, I can eliminate choices 3 and 5, since these dissolve into parts that don't even appear on my acid-base table. They aren't going to be acidic or basic in solution; they're actually salts resulting from neutralization reactions. Choice 1 is also a salt, so we can eliminate that choice. We are left with choices 2 and 4. Choice 2 has the higher hydroxide concentration (0.2 M * 2, the subscript of hydroxide) so it appears that solution would be the least favorable to calcium hydroxide dissolution since solution 2 is already very basic, which seems to be the exact opposite environment of an solution environment favorable to metal hydroxide dissolution.