Mixtures and Solutions Notes

I. Types of Mixtures

  • Mixture: A physical blend of substances.

A. Heterogeneous Mixtures

  • Defined as mixtures with separate phases (parts).

    1. Suspension

    • A heterogeneous mixture that settles if left alone.

    • Has the largest particle sizes of all mixtures.

    • Can be easily filtered.

    1. Thixotropic Mixture

    • Settles into a bottom soil phase and top liquid phase.

    • Flows like a liquid when stirred and sits like a solid when left alone.

    1. Colloid (Colloidal Suspension)

    • Heterogeneous mixture with intermediate particle sizes.

    • Cannot be filtered or settled.

    • Exhibits Brownian motion (random movements).

    • Electrostatic layers form around particles.

    • Examples: Aerosols, emulsions, pastes, gels, foams, etc.

    • Tyndall Effect: Visible light is scattered by colloidal particles, showing a path through colloids and suspensions, but not through true solutions.

    • Emulsions are colloidal dispersions of liquids in liquids and require an emulsifier (e.g., soap).

B. Homogeneous Mixtures (Solutions)

  • Also known as solutions (soln), these are physical mixes with one phase (part).

    1. Aqueous solutions (aq): Water containing dissolved materials.

    2. True solutions do not precipitate or separate into layers.

    3. Parts of a solution:

    • Solute: The substance being dissolved.

    • Solvent: The substance doing the dissolving.

    1. Common solution combinations:

    • Gas-gas, gas-liquid, liquid-liquid, solid-liquid, solid-solid.

    1. Solubility:

    • Soluble: Dissolvable.

    • Insoluble: Not dissolvable.

    • Miscible: Liquids that are soluble in each other.

    • Immiscible: Liquids that are not soluble in each other.

    1. Concentration:

    • Dilute: More solvent than solute (weaker).

    • Concentrated: More solute than solvent (stronger).

II. Particle Size Comparison

  • Order from smallest to largest:
    ext{solution} < ext{colloid} < ext{suspension}

  • Examples:

    • Salt water (solution)

    • Whipped cream (colloid)

    • Dirt in water (suspension)

III. Water Molecule Characteristics

A. Properties

  • Colorless and odorless.

  • Neutral pH of 7.

  • Triatomic (3 atoms) with an angular shape.

  • Polar nature with δ+ and δ- areas.

  • Hydrogen bonds: Attraction between hydrogen and an electronegative element of another molecule.

  • Surface tension: Attraction between molecules creates beading in water.

    • Surfactants reduce surface tension by breaking hydrogen bonds.

  • Capillarity: Movement against gravity, important in roots.

  • High specific heat: 4.184 ext{ J/g°C} .

  • High boiling point: 100 °C.

IV. Solution Concentration

A. Definition

  • Concentration [C]: Amount of solute divided by the amount of solvent.

B. Molarity (M)

  1. M = rac{ ext{moles of solute}}{ ext{liters of solution}}

  2. Example 1: What is the molarity of a solution with 0.6784 mol NaCl in 4.5 L?

    • M = rac{0.6784 ext{ mol NaCl}}{4.5 ext{ L}} = 0.15 M

  3. Example 2: Sugar solution with 12.5 g of C12H22O11 in 500.00 mL of water.

    • 0.0730 M

  4. Example 3: How many grams of KBr for a 3.0 M solution in 977.6 mL?

    • 350 ext{ g KBr}

C. Molality (m)

  1. m = rac{ ext{moles of solute}}{ ext{kg of solvent}}

  2. Example 4: For 65.00 g sucrose in 800.0 mL of water, molality is 0.2374 ext{ m} .

  3. Example 5: How many grams of NaCl for a 1.50 m solution in 500.0 mL?

    • 43.8 ext{ g NaCl}

V. Solvent and Solvation

A. Solvation

  • The process of dissolving a solute into a solvent.

    • Hydration: Specific charctersitics when water is the solvent.

    • Water can successfully hydrate both anions and cations based on the polarity.

B. Factors Increasing Solvation Rate

  1. Surface area: Increase by crushing solids.

  2. Agitation: Stirring or shaking.

  3. Temperature: Higher temperatures typically increase solvation.

C. Examples of Solutions

  1. Gas-gas: Atmospheric air

  2. Gas-liquid: Carbonated water

  3. Liquid-liquid: Alcohol in water

  4. Solid-liquid: Sugar in water

  5. Solid-solid: Metal alloys (e.g., brass)

VI. Solubility

A. Definition

  • The maximum amount of solute that dissolves in a certain amount of solvent.

B. Types of Solutions

  1. Unsaturated: Small amount of solute, completely dissolved.

  2. Saturated: Too much solute, excess settles.

  3. Supersaturated: Unstable solution, formed from heating and can recrystallize upon cooling.

VII. Electrolytes & Nonelectrolytes

  • Electrolytes: Conductors in solution (ionic compounds, acids).

    • Weak electrolyte: Small fraction as free ions.

    • Strong electrolyte: Almost all as free ions.

  • Nonelectrolytes: Non-conductors (molecular/organic compounds).

VIII. Water of Hydration

  • Water of hydration: Water integrated into a crystalline structure.

    • Hydrate: Compound with water (e.g., ext{CuSO}4 ullet 5 ext{H}2 ext{O} ).

    • Anhydrous: A hydrate without water (e.g., ext{Na}2 ext{SO}4 ullet 2 ext{H}_2 ext{O} ).

    • Efflorescence & Hygroscopic substances are related to water release and absorption.

IX. Colligative Properties of Solutions

  • Related to the number of solute particles.

  1. Vapor pressure lowering: Affected by the presence of solute.

  2. Boiling point elevation: ext{Δ}Tb = Kb imes m

  3. Freezing point depression: ext{Δ}Tf = Kf imes m

  4. Osmosis: Movement of solvent through a semipermeable membrane from dilute to concentrated solutions.