A mixture that is made by dissolving one compound (solute) in another (solvent) is called a solution. 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. When the amount of solute dissolved in a solvent exceeds the solubility, the solution is called supersaturated. Rock candy can be made by dissolving as much sugar in water, as solubility would allow at a high temperature, and then slowly cooling the solution to room temperature. If a thin string is dipped into it and left in the solution, the sugar in excess of the solubility at room temperature will form sugar crystals around the string, making the sweet rock candy. The solubility (in grams of sugar per 100 grams of water) as a function of temperature (in degrees Celsius) is plotted in the graph below.
In order to produce rock candy at 20 degrees Celsius from a solution of 300 g of sugar not completely dissolved in 100 g of water, the solution must be:
- first heated above 60 degrees Celsius, then slowly cooled to 20 degrees Celsius.
- slowly stirred at 20 degrees Celsius.
- slowly cooled to 0 degrees Celsius.
- slowly cooled below 0 degrees Celsius, then heated to 20 degrees Celsius and stirred.
Answer(s): A
Explanation:
The question could be answered by going back to the passage. Rock candy is made by first completely dissolving the excess sugar, at a high temperature, then slowly cooling to room temperature Choices B, C, and D don't describe heating, followed by slow cooling.