Solutions and Concentration

Introduction to Solutions

• Solution: A homogeneous mixture with evenly mixed substances at the molecular or ionic level.
• Significance: Solutions are essential for chemical reactions and various biological and industrial processes.

Distinguishing Solutions, Suspensions, and Colloids

• Solution: Homogeneous with molecules dissolved at a molecular level (e.g., sugar in water).
• Suspension: Heterogeneous with larger particles that settle over time (e.g., muddy water).
• Colloid: Contains intermediate particle sizes that do not settle (e.g., whipped cream).

• Settling:

  • Solutions: Particles remain evenly distributed.
  • Suspensions: Particles settle over time.
  • Colloids: Particles remain dispersed without settling.

• Light Interactions:

  • Solutions: Appear clear with no light scattering.
  • Suspensions: Appears cloudy as particles block light.
  • Colloids: Exhibit the Tyndall effect, scattering light, giving a foggy look.

Methods of Separation

• Filtration:
  • Suspensions: Can be separated by filtration.
  • Solutions: Cannot be filtered; components are uniformly mixed.

Components of a Solution

• Solution: A homogeneous mix of solute and solvent.

• Components:

  • Solute: Present in a lesser amount and is the substance being dissolved (e.g., sugar in tea).
  • Solvent: Present in a greater amount and dissolves the solute (e.g., water).

• Roles and States:

  • Solute: Affects characteristics such as taste and pH.
  • Solvent: Facilitates chemical reactions and influences the physical state.
  • State Examples:
    • Solid in Liquid (e.g., salt in water)
    • Gas in Liquid (e.g., CO₂ in soda)
    • Liquid in Liquid (e.g., ethanol in water)

Solubility and Molecular Interactions

• Intermolecular Forces:

  • Hydrogen Bonds: Vital for solvents like water.
  • Van der Waals: Play a role in non-polar compounds.
  • Dipole-Dipole: Affect solubility among polar molecules.

• Solute Distribution:

  • Even solute distribution leads to a homogeneous mixture.

Solubility Effects

• Temperature:

  • Solids: Solubility generally increases with temperature.
  • Gases: Solubility typically decreases as temperature rises.

• Pressure:

  • Impacts gas solubility in liquids; increasing pressure typically increases solubility.

• Molecular Polarity:

  • "Like dissolves like": Polar solvents dissolve polar solutes effectively.

Observing and Measuring Solution Concentration

• Molarity:

  • Definition: Moles of solute per litre of solution.
  • Formula: $M = \frac{\text{moles of solute}}{\text{litres of solution}}$

• Methods:

  • Percentage Concentration (% m/v): Mass of solute per 100 mL of solution.
  • Parts per Million (ppm): Mass of solute per million parts of solution.

Conducting Titrations

• Process:
  • Fill a burette with titrant.
  • Add titrant to analyte until the endpoint is reached.

Sample Problem: Calculating Molarity

Example: Calculate the molarity of a solution containing 10 moles of solute in 5 litres of solution.

Solution:

1. Use the molarity formula: $M = \frac{\text{moles of solute}}{\text{litres of solution}}$
2. Substitute the values: $M = \frac{10 \text{ moles}}{5 \text{ litres}} = 2 \text{ mol/L}$
3. Therefore, the molarity of the solution is 2 mol/L (or 2M).

Example: Calculate the percentage concentration (% m/v) of a solution containing 5g of salt in 250mL of solution.

Solution:

1. Use the formula: % m/v = $\frac{\text{mass (g)}}{\text{volume (mL)}} \times 100$
2. Substitute the values: % m/v = $\frac{5 \text{ g}}{250 \text{ mL}} \times 100 = 2\%$
3. Therefore, the percentage concentration is 2% m/v.

Key Takeaway

• Consistent practice enhances understanding of solution concentrations.

Summary and FAQ

• Main Concepts:
  • Factors affecting solubility include temperature, pressure, and molecular interactions.