Analyzing a Solubility Curve

Analyzing a Solubility Curve

Unit 8: Solutions and Acids and Bases

Understanding Solubility Curves

  • X-axis: Represents the temperature measured in degrees Celsius (°C).

  • Y-axis: Represents the concentration of the solute, expressed in grams of solute per 100 grams of the solvent (here, water).

  • Line Representation:

    • On the line: Indicates the solution is saturated (i.e., it contains the maximum amount of solute that can dissolve at that temperature).

    • Above the line: Indicates a supersaturated solution (i.e., it contains more solute than can normally dissolve at that temperature).

    • Below the line: Indicates an unsaturated solution (i.e., it contains less solute than can dissolve at that temperature).

Example Solubility Curve Problems
Problem 1: KClO₃ Solubility

  • Question: How many grams of KClO₃ can be dissolved in 100 grams of water at 50 °C?

  • Answer: 20 grams of KClO₃.

Solubility Graph Interpretation
Problem 2: Most Soluble Substance at 10 °C

  • Graph Analysis:

    • Substances Represented: KI, NaNO₃, KNO₃, HCl, KCl, NaCl, KClO₃, NH₃, SO₂.

    • Observations:

      • KI shows the highest solubility at 10 °C.

  • Answer: KI is the most soluble substance in 100 grams of water at 10 °C.

Problem 3: Least Soluble Substance at 10 °C

  • Answer: KClO₃ is the least soluble substance in 100 grams of water at 10 °C.

Problem 4: Temperature Effects on Solubility

  • Question: Which substance is most affected by an increase in temperature?

  • Analysis:

    • To determine which substance is most affected by temperature increase, we look for the steepest slope on the solubility curve. The steepness indicates the greatest change in solubility with temperature change.

    • Answer: KNO₃ is most affected by an increase in temperature due to its steep slope on the curve.

Problem 5: Substances with Decreased Solubility with Temperature Increase

  • Question: Identify three substances that become less soluble in water as the temperature increases.

  • Analysis:

    • Observing the curve, we find those with a negative slope as temperature increases.

    • Answer: HCl, NH₃, and SO₂ show decreased solubility with increased temperature.

Problem 6: Solution Characteristics During Temperature Change

  • Scenario: A solution is prepared with 40 grams of NaCl added to 100 grams of water at 90 °C. The solution is then cooled to 40 °C.

  • Analysis:

    • At 90 °C, the solution is saturated (and may contain maximum solute for that temperature).

    • Upon cooling to 40 °C, we must identify the state of the resulting solution:

      • It must be compared to the solubility at 40 °C to determine if it is still saturated, or if it has become supersaturated, meaning it now holds more solute than can dissolve at the lower temperature.

      • Answer: The solution becomes supersaturated when cooled to 40 °C after being saturated at 90 °C.