A solution is prepared by dissolving 12.5 g of KBr in 20 mL of water at 60 °C (see Figure 9.3). Is this solution saturated, unsaturated, or supersaturated? What will happen if the solution is cooled to 10 °C?

Verified step by step guidance

1. Identify the solubility of KBr at 60 °C from the graph. Since KBr is not labeled, use the closest line, which is KCl, as an approximation.
2. Convert the mass of KBr from grams to grams per 100 mL of water. Since 20 mL is used, multiply the mass by 5 to scale up to 100 mL.
3. Compare the calculated solubility of KBr in grams per 100 mL at 60 °C with the solubility line of KCl on the graph to determine if the solution is saturated, unsaturated, or supersaturated.
4. To determine what happens when the solution is cooled to 10 °C, find the solubility of KBr at 10 °C using the same approximation method with the KCl line.
5. Compare the solubility at 10 °C with the amount of KBr in the solution to predict if any KBr will precipitate out as the solution cools.

Key Concepts

Solubility

Solubility refers to the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature. For KBr, solubility increases with temperature, meaning more KBr can dissolve in water as the temperature rises. Understanding solubility is crucial for determining whether a solution is saturated, unsaturated, or supersaturated.

Saturated, Unsaturated, and Supersaturated Solutions

A saturated solution contains the maximum amount of solute that can dissolve at a given temperature, while an unsaturated solution can still dissolve more solute. A supersaturated solution contains more solute than is typically soluble at that temperature, achieved by dissolving solute at a higher temperature and then cooling it. Identifying the state of a solution is essential for predicting its behavior when conditions change.

Temperature Effects on Solubility

Temperature significantly affects the solubility of most solids in liquids; generally, higher temperatures increase solubility. The provided graph illustrates how the solubility of KBr changes with temperature, indicating that cooling a saturated solution may lead to precipitation of the solute. Understanding this relationship helps predict what happens to a solution when its temperature is altered.