2.2 Solutions and solubility

Chapter Overview

  • Chapter 2 discusses the properties of materials, focusing on solutions and solubility.

2.2 Solutions and Solubility

Key Learnings

  • Make solutions of varying concentrations.

  • Compare the number of solute particles in solutions of different concentrations.

  • Investigate the solubility of various substances.

Learning Objectives

  • Understand terms: concentrated, dilute, insoluble, saturated, solubility, soluble, solution.

Solutions

  • A solution is formed when a solute dissolves in a solvent.

  • Concentrated solutions contain more solute particles than dilute solutions.

Solubility

  • A solid that dissolves in water is termed soluble (e.g., sodium chloride and sugar).

  • Solids that do not dissolve in water are termed insoluble (e.g., iron filings).

  • A saturated solution is when no more solute can dissolve in the solvent.

Comparing Solubility

  • To compare solubility, measure the amount of solute that dissolves in a specific solvent amount.

  • Example: Solubility measurements at 20 °C for 100 g of water for various salts show differences in how much can dissolve.

Relative Solubility

  • Some substances are more soluble than others.

  • For instance, sodium chloride is more soluble in water than potassium chloride at 25 °C.

Other Solvents

  • Not all substances dissolve in water. For example, oil paints require solvents like methanol for cleaning brushes.

Temperature & Solubility

  • Most solutes dissolve better in hot water than cold.

  • As temperature increases, solubility typically increases.

  • Example: 204 g of sugar dissolve in 100 g of water at 20 °C; at 80 °C, up to 362 g can dissolve.

Comparing Salts Solubility Graph

  • A graph illustrating solubility of potassium nitrate, sodium nitrate, and copper sulfate at various temperatures indicates trends in solubility based on temperature.

Worked Example

  • If 204 g of sugar dissolves in 100 g of water at 20 °C:

  • a) In 200 g of water: 408 g of sugar will dissolve.

  • b) In 50 g of water: 102 g of sugar will dissolve.

Questions for Review

  • Trend observation for solubility of all three salts.

  • Solubility values at varying temperatures for potassium nitrate.

  • Identify the most soluble salt at 10 °C and at 80 °C.