A KNO₃ solution containing 45 g of KNO₃ per 100.0 g of water is cooled from 40 °C to 0 °C. What happens during cooling? (Use Figure 13.11.)

Key Concepts

Solubility

Solubility refers to the maximum amount of a solute that can dissolve in a solvent at a given temperature and pressure. In the case of KNO3, its solubility decreases as the temperature drops, meaning that less KNO3 can remain dissolved in water at lower temperatures. Understanding solubility is crucial for predicting whether a solution will remain saturated or if precipitation will occur when cooled.

Saturation and Precipitation

A saturated solution is one where the maximum amount of solute has been dissolved in the solvent at a specific temperature. When a saturated solution is cooled, it may exceed its solubility limit, leading to precipitation, where the excess solute forms solid crystals. This concept is essential for understanding the changes that occur in the KNO3 solution as it cools from 40 °C to 0 °C.

Cooling Effects on Solutions

Cooling a solution affects the kinetic energy of the molecules, which can lead to changes in solubility and the state of the solute. As temperature decreases, the solute's ability to remain dissolved diminishes, potentially resulting in crystallization. This principle is important for analyzing the behavior of the KNO3 solution as it transitions from a warmer to a cooler state.