Chemistry Chapter on Aqueous Solutions

Chapter Overview

• Solutions are crucial in various chemical, biological, and industrial applications.
• Aqueous solutions (where substances dissolve in water) are a focus of this chapter.
• Solutions can involve all states (gas-gas, solid-solid, liquid-solid, liquid-liquid).
• This chapter primarily concentrates on aqueous solutions.

Tragedy in Cameroon - Lake Nyos

• In 1986, a gas cloud from Lake Nyos (Cameroon) killed over 1,700 people.
• The gas was primarily carbon dioxide, released after a lake overturn.
• The carbon dioxide was dissolved in the water and released into the atmosphere.
• The incident prompted investigations into other African lakes, specifically Lake Kivu.

Solutions - Homogeneous Mixtures

• The major component of a solution is the solvent.
• The minor component of a solution is the solute.
• The overall phase of a solution is identical to the solvent's phase.
• Examples:
  • Salt water: solid NaCl in liquid water
  • Air: gaseous O2 in gaseous N2
• Table 13.2.1 demonstrates various solution types with illustrations.

Like Dissolves Like

• Polar compounds dissolve polar compounds.
• Nonpolar compounds dissolve nonpolar compounds.
• Polar compounds do not dissolve in nonpolar compounds, and vice versa.
• This principle is summarized in Table 13.2.2.
• Intermolecular forces (London dispersion forces, dipole-dipole interactions, hydrogen bonding) determine solubility.

Solutions of Solids Dissolved in Water

• Solubility is the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature.
• A saturated solution is one where the maximum amount of solute is dissolved.
• These solutions are saturated or unsaturated.
• The solubility of solids typically increases with temperature.
• Supersaturated solutions can hold more solute than their saturated counterparts.
• Table 13.3.1 lists the solubility of specific ionic compounds.

Electrolyte Solutions

• Electrolytes are compounds that yield ions in solution.
• Strong electrolytes dissociate nearly completely in solution.
• Weak electrolytes dissociate partially.
• Nonelectrolytes do not dissociate.
• Conductivity measurements can distinguish these types of solutions.
• Table 13.3.2 displays conductivity examples.

Solutions of Gases in Water

• Gas solubility typically decreases with increasing temperature.
• Gas solubility increases with increased pressure.
• Thermal pollution (e.g., hot water discharge from industries) can decrease the amount of dissolved oxygen in water, impacting aquatic life.
• This is described by Henry's law and Figure 13.4.1.

Specifying Solution Concentration - Mass Percent

• Mass percent (%m/m) = (mass of solute / mass of solution) * 100%
• Quantitative expressions for solution concentration.
• Allows measuring ratios of solute to solution.

Specifying Solution Concentration - Molarity

• Molarity (M) = (moles of solute / liters of solution).
• A crucial concentration expression for chemical calculations.

Solution Dilution

• M1V1 = M2V2.
• M1 & M2 represent initial and final concentrations, while V1 & V2 represent initial and final volumes.
• Diluting a solution involves adding more solvent without altering the amount of solute.

Solution Stoichiometry

• Using concentration to calculate reactant/product amounts in solution-based reactions.

Freezing Point Depression and Boiling Point Elevation

• Colligative properties depend on solute concentration.
• Freezing point of solutions is lower than the pure solvent.
• Boiling point of solutions is higher than the pure solvent.
• Formulas for freezing point depression and boiling point elevation involve molality and van't Hoff factor.

Osmosis

• Osmosis is the solvent's movement across a semipermeable membrane from a lower to a higher concentration of solute
• Osmotic pressure is directly related to solute concentration and is crucial in biological systems.
• Osmosis explains why IV fluids must be isotonic to prevent cell damage.