Pure Substances
Matter with constant composition and distinct properties.
- Elements: Cannot be broken down chemically. Made of one type of atom (e.g., \(Au, O_2\)).
- Compounds: Two or more elements chemically bonded in fixed ratio. Properties differ from constituents (e.g., \(H_2O, NaCl\)). Separation requires chemical reaction.
Mixtures
Two or more substances physically mixed. Retain original properties.
- Homogeneous: Uniform composition. One phase. "Solutions" (e.g., Saltwater, Air, Brass).
- Heterogeneous: Non-uniform. Distinct phases (e.g., Salad Dressing, Concrete).
Separation Techniques
Mixtures are separated by physical means. Differences in properties determine the method.
1. Filtration
Insoluble Solid from Liquid
Based on particle size. (e.g. Sand from Water).
2. Evaporation
Soluble Solid from Liquid
Boils off solvent to leave solid. (e.g. Salt from Brine).
3. Solvation
Solubility Difference
Dissolve one component while leaving other insoluble. (e.g. Salt & Sand mixture → Add water).
4. Recrystallization
Purification Technique
Dissolve impure solid in hot solvent. Cool slowly. Pure crystals form, leaving impurities in solution.
5. Chromatography
Affinity for Stationary vs Mobile Phase
Formula: \( R_f = \frac{\text{dist. spot}}{\text{dist. solvent}} \)
6. Distillation (Simple & Fractional)
Boiling Point Differences
Simple: Keep the solvent (e.g., pure water from seawater).
Fractional: Separate liquids with close B.P.s (e.g., Crude Oil). Uses fractionating column for repeated condensation/evaporation cycles.