Properties of Solutions

Solutions

  • A homogenous mixture has a uniform composition throughout.
  • Solute: Substance that dissolves in the solution, usually in a smaller amount.
  • Solvent: Substance in which the solute dissolves, usually in a greater amount.
  • "Like dissolves like" rule: Applied in solubility; a solution forms when attractive forces within the solute are similar to those within the solvent.
  • Soluble: Solid in liquid, gas in liquid.
  • Insoluble: Solid in liquid, gas in liquid (does not dissolve or mix).
  • Miscible: Liquid in another liquid.
  • Immiscible: Liquid in another liquid (does NOT mix).

Solubility

  • A measure of how well one substance dissolves in another.
  • Solutions can be classified according to the amount of solute dissolved relative to the amount that can be dissolved.

Types of Solutions

  • Saturated solutions: Contain the maximum amount of dissolved solute at a given temperature in the presence of undissolved solute.
  • Unsaturated solutions: Contain less solute than a saturated solution under the same conditions.
  • Supersaturated solutions: Contain more dissolved solute than a saturated solution under the same conditions.

Types of Solutions (Examples)

  • Gaseous Solutions (Gas in gas)
    • Example: Air
    • Solute: Oxygen and other gases
    • Solvent: Nitrogen
  • Liquid Solutions
    • (Gas in liquid)
      • Example: Soda water
      • Solute: Carbon dioxide
      • Solvent: Water
    • (Liquid in liquid)
      • Example: Antifreeze
      • Solute: Ethylene glycol
      • Solvent: Water
    • (Solid in liquid)
      • Example: Seawater
      • Solute: Sodium chloride
      • Solvent: Water
  • Solid Solutions
    • (Liquid in solid)
      • Example: Dental amalgam
      • Solute: Mercury
      • Solvent: Silver
    • (Solid in solid)
      • Example: Steel
      • Solute: Carbon
      • Solvent: Iron
    • (Gas in solid)
      • Example: Charcoal filter
      • Solute: Poisonous gases
      • Solvent: Carbon

Concentration of Solutions

  • Solutions can be described qualitatively or quantitatively based on the amount of solute to a given amount of solvent.
  • Qualitatively
    • Dilute
    • Concentrated
  • Quantitatively
    • Measures of solution concentrations are necessary.
    • There are many ways of expressing the quantity of solute present in each amount of solvent.

Concentration Units

  • Parts per million (ppm)
    • A unit for expressing very dilute concentrations.
    • Commonly used to express the concentration of pollutants in air or water.
    • Formula: ppm \text{ of component} = \frac{\text{volume of component}}{\text{total volume of solution}} \times 10^6
  • Parts by mass
    • Formula: \text{Mass %} = \frac{\text{mass of solute}}{\text{mass of solution}} \times 100
  • Parts by volume
    • Formula: \text{Volume %} = \frac{\text{volume of solute}}{\text{volume of solution}} \times 100
  • Mole Fraction
    • Formula: \text{Mole fraction} = \frac{\text{moles of solute}}{\text{moles of solution}}
  • Molarity
    • Most common way of expressing the concentration of a solution.
    • Defined as the number of moles of solute per liter of solution.
    • Formula: \text{Molarity} = \frac{\text{moles of solute}}{\text{volume of solution}}
    • Volume is affected by temperature.
  • Molality
    • Number of moles of solute dissolved per kilogram of solvent.
    • Formula: \text{molality} = \frac{\text{moles of solute}}{\text{mass of solvent}}
    • Mass does not change with temperature.

Example Calculations

  • ppm Example: If 100L of a gas mixture over a metropolitan area contains 0.0600L of CO, the concentration in ppm CO is calculated as follows: ppm = (0.0600L / 100L) * 10^6
  • Mass Percent Example: A solution is prepared by dissolving 10g of NaCl in 100g of water. The percentage by mass of NaCl in the solution is: \text{Mass %} = \frac{10g}{10g + 100g} \times 100
  • Volume Percent Example: 15mL of alcohol is mixed with 85mL of water. The volume percent of solution is: \text{Volume %} = \frac{15mL}{15mL + 85mL} \times 100
  • Molarity Examples
    • What is the molarity of a solution that was prepared by dissolving 82.0 \text{ g} of CaCl_2 in enough water to make 812 \text{ mL} of solution?
    • What is the molarity of a solution that contains 5.5 \text{ g} of HCl dissolved in enough water to make 250 \text{ mL} of solution?
    • What is the molarity of a solution that was prepared by dissolving 14.2 \text{ g} of NaNO_3 in enough water to make 350 \text{ mL} of solution?
    • How many grams of NaBr would be needed to prepare 700 \text{ ml} of 0.230 \text{ M } NaBr solution?
  • Molality Examples
    • What is the molality of a solution in which 3.0 moles of NaCl is dissolved in 1.5 \text{ kg} of water?
    • What is the molality of a solution in which 15 \text{ g} of I_2 is dissolved in 500 \text{ g} of alcohol?
    • What is the molality of iron (III) chloride in a solution that is prepared by dissolving 17.339 \text{ g} of iron (III) chloride in 454.2 \text{ g} of water?
  • Comprehensive Example: A solution is prepared by dissolving 4.00g of NaOH in 100.00g of water. The volume of the resulting solution is 102.00mL. Calculate:
    • Mole fraction
    • Molarity
    • Molality
    • Mass percent of NaOH

Dilutions

  • The process of lowering the concentration of a solute in a solution by simply adding more solvent to the solution, such as water.
  • Stock solutions: Concentrated solutions in the laboratory with a known molar concentration and are diluted to a lower concentration for actual use in the experiment.
  • N_{\text{solute}} = M \times V
  • Number of moles before dilution = number of moles after dilution
  • N{\text{before}} = N{\text{after}}
  • M1V1 = M2V2

Dilution Examples

  • How would you prepare a 0.1M \text{ } HCI solution from 10mL of a 0.5M \text{ } HCI stock solution?
  • Calculate the molarity of each aqueous solution:
    • 75.0mL of 0.250M \text{ } NaOH diluted to 0.250L with water.
    • 35.5mL of 1.3M \text{ } HN_3 diluted to 0.150L with water.