Chemistry Solutions and Solubility Factors

Types of Solutions

• Solutions are homogeneous mixtures of two or more substances. The substance present in the largest amount is the solvent, while the other substances are solutes.
• Solutions can exist in various states: solid (e.g., alloys), liquid (e.g., saltwater), or gas (e.g., air).
• The solvent's properties dictate the solution's overall properties, such as its boiling point and freezing point.

Factors Affecting Solubility

• Solubility is the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature and pressure.
• Several factors influence solubility:
  • Temperature: Generally, solubility of solids in liquids increases with temperature. Gases become less soluble in liquids as temperature increases.
  • Pressure: Solubility of gases in liquids is directly proportional to pressure (Henry's Law). Increased pressure increases the solubility of the gas.
  • Nature of solute and solvent: "Like dissolves like" is a general rule. Polar solvents dissolve polar solutes, and nonpolar solvents dissolve nonpolar solutes.

Concentration Units

• Concentration expresses the amount of solute in a given amount of solvent or solution. Several units are used:
  • Molarity (M): Moles of solute per liter of solution.
  • Molality (m): Moles of solute per kilogram of solvent.
  • Percentage by mass (% w/w): Mass of solute divided by mass of solution, multiplied by 100.
  • Percentage by volume (% v/v): Volume of solute divided by volume of solution, multiplied by 100.
  • Parts per million (ppm): Mass of solute divided by mass of solution, multiplied by 10^6.
  • Parts per billion (ppb): Mass of solute divided by mass of solution, multiplied by 10^9.

Colligative Properties

• Colligative properties are properties of solutions that depend on the number of solute particles, not the identity of the solute.
  • Vapor pressure lowering: The presence of a nonvolatile solute lowers the vapor pressure of the solvent.
  • Boiling point elevation: The presence of a nonvolatile solute raises the boiling point of the solvent.
  • Freezing point depression: The presence of a nonvolatile solute lowers the freezing point of the solvent.
  • Osmotic pressure: The pressure required to prevent the net flow of solvent across a semipermeable membrane.

Solution Formation

• Dissolution is a process involving the interaction between the solvent and solute molecules.
• The driving forces behind dissolution include:
  • Enthalpy changes associated with the breaking of solute-solute interactions, solvent-solvent interactions, and the formation of solvent-solute interactions.
  • Entropy increases often favor dissolution. The increase in disorder when the solute and solvent mix generally contributes to the solubility.

Electrolytes

• Electrolytes are substances that dissolve in water to form solutions that conduct electricity.
  • Strong electrolytes completely dissociate into ions in solution.
  • Weak electrolytes partially dissociate into ions.
  • Non-electrolytes do not dissociate into ions in solution.

Precipitation Reactions

• Precipitation reactions involve the formation of an insoluble solid (precipitate) when two solutions are mixed.
• The solid forms because of the low solubility of the product in that solvent. Knowledge of solubility rules is essential for predicting precipitation reactions.