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 14.11.)

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Identify the solubility of KNO3 at 40 °C using Figure 14.11. This will tell you how much KNO3 can dissolve in 100 g of water at this temperature.

Determine the solubility of KNO3 at 0 °C using the same figure. This will indicate how much KNO3 can remain dissolved in 100 g of water at the lower temperature.

Compare the initial concentration of KNO3 (45 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 become supersaturated upon cooling.

If the solution becomes supersaturated upon cooling, predict that excess KNO3 will precipitate out of the solution until the concentration matches the solubility at 0 °C.

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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. 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 Point

The saturation point is the concentration of a solute in a solution at which no more solute can dissolve at a specific temperature. When a solution is cooled, it may reach a point where the amount of dissolved KNO3 exceeds its solubility limit, leading to the formation of solid KNO3 crystals. Recognizing the saturation point helps in understanding the behavior of solutions during temperature changes.

Crystallization

Crystallization is the process by which dissolved solute comes out of solution and forms solid crystals. As the KNO3 solution cools, the solubility decreases, and excess KNO3 may crystallize out of the solution. This process is important in various applications, including purification and the formation of solid compounds from solutions.

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