Overview
This lecture introduces the chapter "Solutions" in chemistry, focusing on types of mixtures, classification of solutions, detailed discussion of true (liquid) solutions, and methods to express concentration.
Types of Mixtures and Solutions
- Three types of mixtures: true solution, colloidal solution, and suspension.
- True solution: homogeneous mixture, uniform distribution (e.g., NaCl in water).
- Colloidal solution: heterogeneous, non-uniform, dispersed phase (e.g., oil in water).
- Suspension: heterogeneous, particles settle (e.g., clay in water).
- Only true solutions are studied in detail for this chapter.
Fundamentals of True Solutions
- True solution: homogeneous, uniform composition, single phase throughout.
- Binary solution: contains two components—solute and solvent.
- Solvent: the phase matching the solution and usually present in greater amount.
- True solutions can be solid, liquid, or gaseous.
Liquid Solutions: Classification and Examples
- Focus is on liquid solutions (liquid as solvent).
- Three cases for solutes in liquid solutions:
- Solid in liquid (e.g., urea in water)
- Liquid in liquid (e.g., benzene in toluene)
- Gas in liquid (e.g., Nâ‚‚ in water)
- Questions often ask to identify solvent (usually the component matching the phase of solution, not necessarily in higher proportion).
Concepts of Concentration
- Concentration expresses the relative amount of solute in solvent/solution.
- Common terms for expressing concentration:
- Grams per liter (strength)
- Percent w/w, w/v, v/v
- Molarity (M), formalities (F), normality (N), molality (m)
- PPM (parts per million), mole fraction, volume strength
Calculation and Meaning of Concentration Terms
- Grams per liter: x grams of solute in 1 liter solution; ratio, not an absolute value.
- Percent w/w: x grams solute in 100 grams solution.
- Percent w/v: x grams solute in 100 ml solution.
- Percent v/v: x ml solute in 100 ml solution.
- These ratios can be scaled; actual amounts require knowing total solvent/solution volume.
- Concentration values often unitless (ratios, percentages).
Molarity: Definition and Properties
- Molarity (M): moles of solute per liter of solution.
- Molarity is an intensive property (does not depend on amount or size of sample, unless the sample is altered).
- Uniform/true solutions have the same molarity everywhere in the container.
- Absolute quantity of solute can only be determined if both molarity and volume are known.
Intensive vs. Extensive Properties
- Intensive property: does not depend on size/amount (e.g., molarity in a given solution).
- Extensive property: depends on size/amount (e.g., total mass).
- Intensive/extensive checks must be for a given, untampered sample (no addition/removal of solute/solvent).
Key Terms & Definitions
- True Solution — Homogeneous mixture with uniform composition throughout.
- Colloidal Solution — Heterogeneous mixture with dispersed phase not uniformly mixed.
- Suspension — Heterogeneous mixture where particles settle out.
- Solvent — Component whose phase matches the solution; usually in greater amount.
- Solute — Component dissolved in the solvent.
- Molarity (M) — Number of moles of solute per liter of solution.
- Percent w/w — Mass of solute per 100g solution.
- Percent w/v — Mass of solute per 100ml solution.
- Percent v/v — Volume of solute per 100ml solution.
- Intensive property — Property independent of amount or size of sample.
Action Items / Next Steps
- Review notes on true solutions and types of concentration expressions.
- Practice sample problems for calculating grams per liter, % w/w, % w/v, and molarity.
- Prepare for next class on liquid solutions and concentration units.