Question

A student conducts an investigation in which she dissolves 1 gram (g) each of several substances in 50 milliliters of water. She has 12 identical plastic cups of water. She places 1 g of salt in three cups, 1 g of sugar in three cups, and 1 g of baking soda in three cups. Three cups contain only water. She places all the cups in a freezer and records the temperature of each cup every 15 minutes for 4 hours.

Which of the following question is the student most likely investigating? a. What effect does cooling have on the solubility of different solutes? b. How is the cooling rate of water affected by different solutes? c. What effect do different concentrations of solute have on the freezing point of water? d. How does the volume of water affect the rate at which it cools?

Answer 1

Answer: c. What effect do different concentrations of solute have on the freezing point of water?

Comments: As per the condition given; the student was definitely investigating the freezing point of water in the presence of different solutes. In the presence of solute in solvent (water) the depression point of the solution decreases. This is the colligative properties of solution which depends on the concentration of solute molecules or ions but not depend on the identity of the solute. The colligative properties are lowering of vapour pressure, the elevation of boiling point, depression of freezing point etc. Solubility increases with the increase of temperature, this was not investigated by the student because they were decreasing the temperature