A KNO3 solution containing 35 g of KNO3 per 100.0 g of water is cooled from 40°C to 0°C. What happens during cooling? (Use Figure 14.11.)

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Identify the solubility of KNO3 at 40°C using the provided solubility chart or figure.

Determine the solubility of KNO3 at 0°C using the same chart or figure.

Compare the initial concentration of KNO3 in the solution (35 g per 100 g of water) with the solubility at 40°C to confirm if the solution is saturated, unsaturated, or supersaturated at the starting temperature.

Compare the initial concentration of KNO3 with the solubility at 0°C to determine if the solution will remain saturated, become unsaturated, or if excess KNO3 will precipitate out as the solution cools.

Conclude what happens to the KNO3 in the solution during the cooling process based on the solubility changes observed.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

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 increases with temperature, meaning more KNO3 can dissolve in water at higher temperatures. As the solution cools from 40°C to 0°C, the solubility decreases, potentially leading to the precipitation of KNO3 if the solution becomes supersaturated.

Saturation and Supersaturation

A saturated solution contains the maximum amount of solute that can dissolve at a specific temperature. When a solution is cooled, it may become supersaturated if it contains more solute than the new solubility limit allows. This condition can lead to the formation of solid crystals as the excess solute precipitates out of the solution, which is a key process to consider when cooling the KNO3 solution.

Crystallization

Crystallization is the process by which solute particles come together to form a solid crystal structure from a solution. As the KNO3 solution cools and becomes supersaturated, the solute begins to crystallize out of the solution. This process is influenced by factors such as temperature, concentration, and the presence of impurities, which can affect the size and quality of the crystals formed.

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Textbook Question

A KNO3 solution containing 35 g of KNO3 per 100.0 g of water is cooled from 40 °C to 0 °C. What happens during cooling? (Use Figure 14.11.)

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Textbook Question

A solution contains 35 g of NaCl per 100.0 g of water at 25°C. Is the solution unsaturated, saturated, or supersaturated? (Use Figure 14.11.)