Chapter 11: Solutions, Molarity & Other Concentrations

1. Definitions of Key Terms

• Solution: A homogeneous mixture of two or more substances.

  • Solvent: The major component of a solution.

  • Solute: The minor component of a solution.

• Concentration: The quantification of how much solute is present in a given amount of solvent.

  • Dilute: A solution with low solute concentration.

  • Concentrated: A solution with high solute concentration.

• Solubility: Maximum amount of solute that can be dissolved in a given amount of solvent.

  • Relationship to solutions:

    • Saturated: Contains maximum solute dissolved.

    • Unsaturated: Contains less than maximum solute dissolved.

    • Supersaturated: Contains more than the normally achievable maximum solute dissolved.

2. Quantitative Units of Concentration

• Molarity (M): Number of moles of solute divided by liters of solution.

• Molality (m): Number of moles of solute per kilogram of solvent.

3. Calculations of Molarity

• Example Calculation 1:

  • Given: 2.50 L of sulfuric acid solution contains 1.26 mol of H2SO4.

  • M = moles of solute / liters of solution = 1.26 mol / 2.50 L = 0.504 M.

• Example Calculation 2:

  • Given: 6.5 g sodium hydroxide in 0.45 L solution.

  • Molar mass of NaOH = 40.0 g/mol(6.5 g NaOH / 40.0 g/mol = 0.163 mol NaOH).

  • M = 0.163 mol / 0.45 L = 0.36 M.

• Example Calculation 3:

  • Given: 32.7 g NaOH in 445 mL solution.

  • Convert 445 mL to Liters: 0.445 L.

  • Convert mass to mol: 32.7 g NaOH / 40.0 g/mol = 0.818 mol.

  • M = 0.818 mol / 0.445 L = 1.84 M.

4. Examples of Calculating Moles from Molarity

• Given: 0.108 L of a 0.887 M NaCl solution.

  • Moles of NaCl = 0.887 M x 0.108 L = 0.0958 mol.

• Given: To find required volume for 0.222 mol of NaNO3 at 2.33 M:

  • V = n / C = 0.222 mol / 2.33 M = 0.0953 L = 95.3 mL.

5. Percentages and Parts Per Measurement

• Mass Percentage (% m/m) = (mass of solute / total mass of sample) x 100.

• Parts per Thousand (ppt) = (mass of solute / total mass) x 1000.

• Parts per Million (ppm) = (mass of solute / total mass) x 1,000,000.

• Example Calculation for mass percentage:

  • 87.9 g of Fe in a 113 g sample: (% m/m Fe = (87.9 g / 113 g) x 100 = 77.8%).

6. Colligative Properties of Solutions

• Colligative Properties: Dependent on the number of solute particles.

  • Includes vapor pressure depression, boiling point elevation, and freezing point depression.

• Vapor Pressure Depression: Decrease of vapor pressure of a solvent due to solute.

• Boiling Point Elevation: Increase in boiling point due to solute presence.

• Freezing Point Depression: Decrease in freezing point due to solute presence.

7. Osmosis and Tonicity

• Osmosis: Movement of solvent through a semipermeable membrane until equilibrium.

• Tonicity:

  • Isotonic: Equal concentration, no net movement of water.

  • Hypertonic: Higher solute concentration outside the cell; cell loses water (crenation).

  • Hypotonic: Lower solute concentration outside the cell; cell gains water (hemolysis).

8. Ionic Solutions and Colligative Properties

• Ionic Solutes: Dissociate into ions, increasing particle count and affecting colligative properties.

• van 't Hoff Factor (i): Number of particles a solute produces in solution.

9. Colloids and Suspensions

• Colloids: Large particles in liquid that do not settle; examples include milk and fog.

• Suspensions: Larger particles that settle over time; examples include muddy water.