units of conversions

Units of Concentration for Solutions

  1. Molarity (M)

    • Moles of solute per liter of solution

    • Dependent on temperature, as volume changes with temperature

  2. Molality (m)

    • Moles of solute per kilogram of solvent

    • Not dependent on temperature

  3. Mole Fraction (χ)

    • Fraction of moles:

      • Moles of solute / Total moles in the solution

  4. Parts by Mass

    • Parts per Million (PPM)

      • Grams of solute per million grams of solution

    • Parts per Billion (PPB)

      • Grams of solute per billion grams of solution

Example Calculation

  • Dissolving Urea in Water:

    • 100 grams of urea in enough water to make 1 liter of solution

Calculations:

  1. Molarity Calculation

    • Moles of Urea:

      • 100 grams / 60.1 grams/mole = 1.664 moles

    • Molarity = 1.664 moles / 1 liter = 1.66 M (3 significant figures)

  2. Molality Calculation

    • Mass of Solvent (Water): 985 grams = 0.985 kg

    • Molality = 1.664 moles / 0.985 kg = 1.69 m (3 significant figures)

  3. Mole Fraction Calculation

    • Moles of Water:

      • 985 grams / 18.0 grams/mole = 54.67 moles

    • Mole Fraction = 1.664 moles / (1.664 + 54.67) = 0.0295

  4. Parts per Million Calculation

    • Total mass of solution = mass of urea + mass of water

    • PPM = (100 grams / total grams of solution) * 1,000,000

    • Calculate based on mass proportions to yield PPM.