Question

To make a solution for an experiment, Gunther needs to add 40 g of a solute to 100 g of water. When making the solution at room temperature, he could only add 34 grams before the solute settled out.

What could he do to dissolve the remaining 6 grams of the solute?

Put the solution in an ice bath, dissolve the solute, and let the solution return to room temperature.
Heat the solution, dissolve the solute, and let the solution cool verifying nothing settled out.
Add more water, boil the solution, and dissolve the solute until the some of the water evaporates.
Keep the solution at room temperature, add more water, and dissolve the excess solute.

Answer 1

Heat the solution, dissolve the solute, and let the solution cool verifying nothing settled out.

Reason: solubility of most solids in water increases with temperature, so heating lets you dissolve the extra 6 g. If no crystals form on cooling you will have a supersaturated (metastable) solution at room temperature. The other options either reduce solubility (ice bath), change the required amount of water, or will cause precipitation on cooling.