The amount of solute that can be dissolved in a solvent at a given temperature is called solubility. For most substances, solubility increases with temperature. Rock candy can be made from sugar solutions that have an excess of sugar dissolved. The amount of sugar per 100 grams of water at a given temperature has to be higher than the amount that is normally soluble in order to make rock candy. Based on the solubility of sugar in water as a function of temperature, plotted in the graph, how much sugar would you need to dissolve in 100 grams of water to make rock candy at 40° C?
According to the graph, at 40° C, about 250 grams of sugar can be normally dissolved in 100 grams of water. In order to make rock candy, this amount has to be exceeded.