Chapter 14 - Mixtures and Solutions

Mixtures and Solutions Overview

  • Approximately 42.3% of steel produced annually comes from recycled material.

  • Major component of steel: iron, often combined with nickel, manganese, chromium, vanadium, and tungsten depending on application.

  • Cement: used for concrete and mortar, strong and weather-resistant materials.

  • Annual global concrete production: ~6 billion cubic meters (1 cubic meter per person).

  • BIG Idea: Most gases, liquids, and solids in the world are mixtures.

Types of Mixtures

  • Mixtures can be heterogeneous or homogeneous.

    • Heterogeneous Mixtures: Do not blend smoothly, retain distinct substances.

      • Examples include suspensions and colloids.

      • Suspensions: Contain large particles that settle over time.

        • Example: muddy water.

        • Can form layers (thixotropic behavior) that act like solids under rest and liquids when agitated.

      • Colloids: Intermediate-sized particles (1 nm to 1000 nm) that do not settle and do not exhibit Tyndall effect.

        • Example: milk.

        • Contains a dispersion medium, preventing particles from settling through electrostatic forces.

    • Homogeneous Mixtures: Uniform appearance, solute particles are indistinguishable from solvent.

      • Examples include solutions like air, ocean water, or steel.

Solution Concentration

  • Concentration measured in percentages or in terms of moles (molarity).

    • Concentration communicates how much solute is dissolved in solvent.

    • Common measures of concentration:

      • Percent by mass: extPercentbymass=mass of solutemass of solution×100ext{Percent by mass} = \frac{\text{mass of solute}}{\text{mass of solution}} \times 100

      • Percent by volume: extPercentbyvolume=volume of solutevolume of solution×100ext{Percent by volume} = \frac{\text{volume of solute}}{\text{volume of solution}} \times 100

      • Molarity (M): M=moles of soluteliters of solutionM = \frac{\text{moles of solute}}{\text{liters of solution}}

      • Molality (m): m=moles of solutekilograms of solventm = \frac{\text{moles of solute}}{\text{kilograms of solvent}}

      • Mole Fraction (X):

        • Solute: XA = nA/nA + nB

        • Solvent: XB = nA/nA + nB

Factors Affecting Solvation

  • Solvation depends on temperature, pressure, and polarity.

    • Temperature: Higher temperatures usually increase solubility for solids.

    • Agitation: Stirring increases solvation rate by increasing collisions between solute and solvent molecules.

    • Surface Area: Smaller particles dissolve faster due to greater surface area exposure.

Colligative Properties of Solutions

  • Colligative properties depend on the number of solute particles, not their identity.

    • Boiling Point Elevation: Delta Tb = Kbm

    • Freezing Point Depression: Delta Tf = Kfm

    • Vapor Pressure Lowering: Nonvolatile solutes lower solvent's vapor pressure.

    • Osmotic Pressure: Pressure due to solvent movement across semipermeable membrane.

Practical Applications

  • To prepare solutions:

    • Calculate required mass based on molarity and volume.

    • Dilute concentrated solutions using the dilution equation: M1V1 = M2V2 .

  • Understand real-world relevance, like using salt to melt ice (lowers freezing point) or maintaining saline levels in aquariums for fish health.

Summary of Key Points

  • Types of mixtures include homogeneous and heterogeneous.

  • Concentration of solutions can be expressed various ways affecting the properties of solutions.

  • Solvation factors: temperature, agitation, surface area.

  • Colligative properties impact the boiling point, freezing point, vapor pressure, and osmotic pressure based on solute particle concentration.