Particles and separation
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The Three States of Matter
States: Solid, Liquid, Gas Changes of State: Melting (Solid → Liquid) Freezing (Liquid → Solid) Boiling/Evaporation (Liquid → Gas) Condensation (Gas → Liquid) Sublimation (Solid → Gas)
Particle Arrangement and Movement
Solids: Tightly packed, vibrate in place. Liquids: Loosely packed, move around each other. Gases: Very far apart, move freely and randomly.
Predicting States of a Substance
Solid: Fixed shape and volume. Liquid: Takes the shape of the container but has fixed volume. Gas: Fills the entire container, no fixed shape or volume.
Energy of Particles in States of Matter
Solid: Low energy. Liquid: Medium energy. Gas: High energy.
Changes During State Changes
Movement and Arrangement: Particles gain energy to break bonds (melting/boiling). Particles lose energy and form bonds (freezing/condensation).
Energy Change During State Changes
Energy Change: Energy is absorbed to break intermolecular forces (melting/boiling). Energy is released when forming bonds (freezing/condensation).
Pure Substance vs Mixture
Pure Substance: Single element/compound, sharp melting point. Mixture: Two or more substances, melting point varies.
Melting Point and Purity
Pure Substances: Have a sharp melting point. Mixtures: Melt over a range of temperatures.
Particle Behavior at Melting Point
Pure Substance Melting: Particles gain enough energy to break bonds and move from a solid to a liquid state.
Heating Curve and Melting Point
Flat Line on Heating Curve: Indicates a phase change; temperature stays constant while the substance melts.
Filtration and Crystallisation
Filtration: Separates insoluble solids from liquids (e.g., sand and water). Crystallisation: Separates a solute from a solution by evaporating the solvent (e.g., salt from seawater).
Formation of Crystals During Crystallisation
Crystallisation: As the solvent evaporates, the solute forms crystals due to reduced solubility at lower temperatures.
Filtration Process
Process: Pour mixture through filter paper; solid residue stays behind, liquid passes through. Risk Reduction: Use of gloves, goggles, and careful heating during crystallisation.
Separating Mixtures by Chromatography
Chromatography: Separates substances based on their solubility and affinity for the stationary phase. Mixtures: Produce multiple spots on a chromatogram.
Chromatography Diagrams
Set-up: Spot the sample on a pencil line of chromatography paper, place in solvent. The solvent moves up the paper, separating substances.
Identifying Pure Substances in Chromatograms
Pure Substance: One spot. Mixture: Multiple spots.
Rf Value Calculation
Rf Value: Rf = Distancemovedbysubstance/Distancemovedbysolvent Use: Identify substances by comparing Rf values to known values.
Simple vs Fractional Distillation
Simple Distillation: Used to separate liquids with significantly different boiling points (e.g., water from ink). Fractional Distillation: Used for separating liquids with closer boiling points (e.g., crude oil).
Fractional Distillation Process
Process: Heat the mixture. Vapors rise through a fractionating column. Substances condense at different heights based on boiling points.
Risk in Distillation
Precautions: Use heat sources carefully. Ensure good ventilation. Avoid pressure build-up by not sealing apparatus.
Water for Chemical Analysis
Why No Dissolved Salts?: Salts may interfere with reactions or give false results.
Fresh Water from Seawater
Method: Desalination by distillation. Heat seawater, condense steam to collect fresh water.
Making Water Safe for Drinking
Steps: Filtration: Remove large particles. Sterilisation: Kill bacteria using chlorine or UV light.
Evaluating Water Purification Risks
Risk: Contamination, harmful chemicals in water. Control: Use appropriate purification techniques like filtration, distillation, and sterilisation.