Final answer:
The likely reason for the change is that the heat caused a different precipitate to form, due to temperature effect on solubility and Le Châtelier's principle for exothermic reactions.
Step-by-step explanation:
The likely reason for the change in the experiment when the students heated both solutions to 50°C compared to the initial experiment at 20°C is The heat caused a different precipitate to form. Since solubility generally increases with temperature due to increased molecular motion and solvation energies, the increase could allow more solute to dissolve before reaching saturation. However, if a reaction is exothermic, applying heat can drive the equilibrium towards the reactants, decreasing solubility in some cases according to Le Châtelier's principle. This effect is illustrated by the example of MgF2 being less soluble at a higher temperature due to its exothermic dissolution. Dissolution processes and temperature changes can significantly affect the direction and extent of chemical reactions and solubility.