COLLIGATIVE-PROPERTIES-OF-SOLUTION

Solute and Solvent Identification

  • Coffee with sugar

    • Solute: Sugar

    • Solvent: Coffee (water base)

  • Carbonated beverage

    • Solute: Carbon dioxide (gas)

    • Solvent: Water

  • 100 ml of Acetic Acid and 50 ml of water

    • Solute: Acetic Acid

    • Solvent: Water

  • 20 moles of acetone and 20 moles of water

    • Solute: Acetone

    • Solvent: Water

  • 70 g of Chromium and 5 g of Molybdenum

    • Solute: Chromium

    • Solvent: Molybdenum

  • Amalgam (mercury in silver)

    • Solute: Mercury

    • Solvent: Silver

Colligative Properties of Solutions

Objectives

  • Identify different colligative properties of solutions.

  • Solve problems involving the colligative properties of solutions.

  • List real-life applications of colligative properties.

Fact or Bluff Activity

  1. The solution of the nonvolatile nonelectrolyte solutes boils at lower temperature than pure solvents. (False)

  2. The vapor pressure of solvent increases when solute is dissolved into it. (False)

  3. The freezing point of a solution is always lower than the freezing point of the pure solvent. (True)

  4. If two solutions are of unequal osmotic pressures, the more concentrated solution is said to be hypotonic. (False)

  5. The equations used in computing for the colligative properties of electrolyte and nonelectrolyte solutions are the same. (False)

Definition of Colligative Properties

  • Properties depend only on the number of solute particles in the solution, not on solute nature.

  • Includes properties that rely on the concentration of solute.

Colligative Properties of Non-electrolyte Solutions

Vapor-Pressure Lowering

  • Nonvolatile solute decreases vapor pressure compared to pure solvent.

  • Raoult's law:

    • P1 = X1 P°1

      • P1: Vapor pressure of solution

      • X1: Mole fraction of solvent

      • P°1: Vapor pressure of pure solvent

Calculating Vapor Pressure Lowering

  1. Given: 218 g of glucose, molar mass = 180.2 g/mol, 460 mL of water, density 1.00 g/mL.

  2. Calculate moles of solute and solvent:

    • n1 (water) = 25.5 mol; n2 (glucose) = 1.21 mol

  3. Mole fraction of water, X1: 0.955

  4. Calculate solution vapor pressure:

    • P1 = 0.955 x 31.82 mmHg = 30.4 mmHg

  5. Vapor pressure lowering: ΔP = (31.82 - 30.4) mmHg = 1.4 mmHg

Understanding Vapor Pressure and Disorder

  • Solutions have greater disorder compared to pure solvents, which affects vaporization.

  • Molecules in a vapor are less ordered than in a liquid, leading to decreased vapor pressure in solutions.

Raoult’s Law for Volatile Solutes

  • When both components are volatile:

    • PA = XA P°A and PB = XB P°B

  • Total pressure:

    • PT = PA + PB

Boiling Point Elevation

  • Boiling point of a solution is higher because of the presence of nonvolatile solutes.

  • Defined as:

    • ΔTb = Tb - T°b

  • Affected by the number of solute particles.

Freezing Point Depression

Definition and Effects

  • The freezing point of a solution is lower than the pure solvent due to solute interference.

  • Defined as:

    • ΔTf = T°f - Tf

  • Example: Salting roads lowers the freezing point of water, useful in winter conditions.

Practical Applications of Colligative Properties

  • Ethylene glycol in antifreeze lowers freezing point; salt on roads aids ice melting.

  • Fruits produce solutes to prevent freezing in cold climates.

  • Homemade ice cream demonstrates freezing point depression through added solutes.