SOLUTIONS

Chemistry of Solutions

Definition of Solutions

  • A solution is a mixture of 2 or more substances in a single phase.

  • One constituent is usually regarded as the solute and the others as the solvent.

Characteristics of Solutions

  • Solutions are homogeneous mixtures of two or more pure substances.

  • In a solution, the solute is dispersed uniformly throughout the solvent.

Components of Solutions

Solute and Solvent

  • Solute: The part of a solution that is being dissolved, usually in a lesser amount.

  • Solvent: The part of the solution that dissolves the solute, usually in a greater amount.

Activity: Identifying Components of Solutions

  1. Air in balloon: Solute - O2, Solvent - N2

  2. Ammonia water: Solute - NH3, Solvent - H2O

  3. Rubbing alcohol (70%): Solute - H2O, Solvent - Isopropyl alcohol

  4. Tincture of Iodine: Solute - Iodine, Solvent - Alcohol

  5. Sea water: Solute - Salt, Solvent - H2O

Types of Solutions

  • Gas in gas: Air

  • Gas in liquid: Soda water (CO2 in H2O)

  • Liquid in liquid: Vinegar (Acetic acid in H2O)

  • Solid in liquid: Sugar in H2O

  • Solid in solid: Brass (Cu in Zn)

Universal Solvent

  • Water (H₂O) is known as the universal solvent.

Formation of Solutions

  1. Solvent molecules are attracted to surface ions.

  2. Each ion is surrounded by solvent molecules (hydration), which facilitates dissolving.

  3. Intermolecular forces are involved in the interactions between solute and solvent.

Types of Solutions Based on Concentration

  • Dilute: Small amount of solute in solvent.

  • Concentrated: Large amount of solute in solvent.

  • Hypotonic: Lower solute concentration.

  • Hypertonic: Higher solute concentration.

  • Isotonic: Equal solute concentrations.

Key Questions on Solutions

  • How does a solid dissolve in a liquid?

  • What drives the dissolution process?

  • What are the energetics involved in dissolution?

What is Dissolution?

  • The process where a solid, liquid, or gas forms a solution in a solvent.

  • In solids, it involves breaking down the crystal lattice into individual ions or molecules.

  • For liquids and gases, compatibility with solvent molecules is necessary.

  • Dissolution is a physical change; evaporating the solvent can recover the original solute.

Solubility

  • Refers to the maximum solute that can dissolve in 100g of water at a specific temperature & pressure.

  • Soluble: Substance that dissolves in a solvent.

  • Insoluble: Substance that does not dissolve in a solvent.

Laboratory Activity on Solubility

  • Determining if substances like sugar, salt, and others are soluble or insoluble in water and other solvents.

Types of Solutions Based on Solubility

  • Saturated solution: Solvent holds as much solute as possible; undissolved solid remains.

  • Unsaturated solution: Less than maximum amount of solute is dissolved.

  • Supersaturated solution: Holds more solute than typically possible; unstable.

Factors Affecting Solubility

  1. Nature of solute and solvent interaction: "Like dissolves like."

  2. Temperature:

    • Solubility of solids usually increases with temperature.

    • For gases, higher temperature decreases solubility.

  3. Pressure:

    • Affects gas solubility; higher pressure increases gas solubility in liquids (Henry's Law).

Concentration Units

  • Percent by mass (m/m): Mass of solute/total mass of solution x 100.

  • Percent by volume (v/v): Volume of solute/total volume of solution x 100.

  • Molarity (M): Moles of solute per liter of solution.

Molarity Calculations**

  • Calculation examples provided illustrating converting grams to moles and calculating molarity.

Dilution**

  • Dilution does not change the number of moles of solute; it increases volume and decreases concentration (Molarity decreases).

  • Formula: M₁V₁ = M₂V₂.

Colligative Properties

  • Properties that depend on the number of solute particles, not their identity.

  • Affect melting point, boiling point, and vapor pressure.

Osmosis**

  • Process where solvent moves through a semi-permeable membrane from a less concentrated to a more concentrated solution.

  • Types of solutions include hypotonic, hypertonic, and isotonic.

Conclusion

  • Understanding solutions is vital for studying chemical reactions, biological processes, and various applications in fields ranging from environmental science to medicine.

  • Review definitions, types, and properties of solutions, as well as key calculations for exams.