Overview
This lecture covers key chemistry concepts related to the properties of solutions, including water's unique behavior, solute/solvent definitions, solution types, concentration calculations, osmosis, diffusion, and active transport.
Water Properties & Polarity
- Water is a polar molecule due to unequal sharing of electrons between oxygen and hydrogen atoms.
- Polarity allows water to form hydrogen bonds with itself and other substances.
- Cohesion: attraction between water molecules, leading to surface tension.
- Adhesion: attraction of water molecules to different substances, helping water "stick" to surfaces.
Solutions: Definitions & Types
- A solution is a homogeneous mixture where solutes are completely dissolved in a solvent.
- Salt and sugar in water form homogeneous solutions; pebbles in water create a heterogeneous mixture.
- Solute: substance present in a smaller amount and dissolved in the solvent.
- Solvent: substance present in a larger amount that dissolves the solute; water is often the solvent.
Solubility: Polar & Nonpolar Substances
- Polar substances (e.g., salt, sugar) dissolve well in water due to partial charges attracting each other.
- Nonpolar substances (e.g., oils, fats) do not dissolve well in water.
Hydrophilic vs. Hydrophobic
- Hydrophilic: "water-loving," substances that dissolve easily in water (usually polar or ionic compounds).
- Hydrophobic: "water-fearing," substances that do not dissolve in water (usually nonpolar substances).
Concentration & Molarity
- Molarity (M): concentration measured as moles of solute per liter of solution (mol/L).
- Example: 9.8 moles NaOH in 3.62 L solution = 2.7 M.
- Dilution equation: M₁V₁ = M₂V₂ (initial and final concentrations/volumes are inversely related).
Osmosis & Tonicity
- Osmosis: passive movement of water through a semi-permeable membrane toward higher solute concentration.
- Hypertonic: higher solute concentration compared to another solution; cells shrink in hypertonic solutions.
- Hypotonic: lower solute concentration compared to another; cells swell in hypotonic solutions.
- Isotonic: equal solute concentration inside and outside the cell; no net water movement.
Diffusion & Facilitated Diffusion
- Diffusion: passive movement of particles from high to low concentration.
- Facilitated diffusion: uses protein channels for molecules that cannot cross the membrane directly; still passive.
Factors Affecting Diffusion Rate
- Shorter distances, higher temperatures, less dense solvents, smaller masses, and permeable barriers increase diffusion rate.
Active Transport
- Active transport moves substances against concentration gradients using energy (ATP) and protein pumps.
- Essential for nutrient uptake, waste removal, and ion balance in cells.
Key Terms & Definitions
- Solution — Homogeneous mixture of solute(s) dissolved in a solvent.
- Solute — Substance dissolved in a solution, present in lesser amount.
- Solvent — Substance that dissolves the solute, present in greater amount.
- Molarity (M) — Moles of solute per liter of solution (mol/L).
- Osmosis — Movement of water across a membrane from low to high solute concentration.
- Diffusion — Movement of particles from high to low concentration.
- Facilitated Diffusion — Passive transport using protein channels.
- Active Transport — Movement of substances against concentration gradient using energy (ATP).
- Isotonic — Solutions with equal solute concentration.
- Hypertonic — Solution with higher solute concentration.
- Hypotonic — Solution with lower solute concentration.
- Hydrophilic — Water-loving; dissolves easily in water.
- Hydrophobic — Water-fearing; does not dissolve in water.
Action Items / Next Steps
- Review definitions and be able to categorize examples as solute, solvent, or solution.
- Practice solution concentration and dilution calculations.
- Study table of solution types (isotonic, hypertonic, hypotonic) and know effects on cells.
- Read textbook sections on osmosis, diffusion, and active transport for further clarification.