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?
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Verified step by step guidance

1. Step 1: Analyze the solubility graph provided. Locate the curve for KBr (potassium bromide). Note that the graph shows solubility in grams of solute per 100 grams of water at various temperatures.
2. Step 2: Convert the given quantities into comparable units. The problem states that 12.5 g of KBr is dissolved in 20 mL of water. Since 20 mL of water is approximately 20 g (assuming the density of water is 1 g/mL), calculate the solubility in grams of KBr per 100 g of water using the formula: \( \text{Solubility} = \frac{12.5}{20} \times 100 \).
3. Step 3: Compare the calculated solubility value to the solubility of KBr at 60 °C from the graph. If the calculated solubility is less than the value on the graph, the solution is unsaturated. If it matches the value, the solution is saturated. If it exceeds the value, the solution is supersaturated.
4. Step 4: Determine what happens when the solution is cooled to 10 °C. Use the graph to find the solubility of KBr at 10 °C. Compare this value to the amount of KBr already dissolved in the solution. If the dissolved amount exceeds the solubility at 10 °C, excess KBr will precipitate out of the solution.
5. Step 5: Summarize the findings. State whether the solution is saturated, unsaturated, or supersaturated at 60 °C, and describe the precipitation process that occurs when the solution is cooled to 10 °C.

Key Concepts

Solubility

Solubility is 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 at higher temperatures. 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, often achieved by heating the solution and then cooling it carefully. Identifying the state of a solution is essential for predicting its behavior when conditions change.

Effect of Temperature on Solubility

Temperature significantly affects the solubility of most solids in liquids; generally, solubility increases with temperature. In the case of KBr, the graph indicates that at 60 °C, a certain amount can dissolve, but if the solution is cooled to 10 °C, the solubility decreases, potentially leading to precipitation of KBr. This concept is vital for understanding the changes in solution behavior with temperature variations.