Cheat Sheet: Exploring Mixtures And Their Separation

1. Introduction and Classification

1.1 Introduction

• Focus: properties, behaviour and separation techniques of mixtures and applications in industry and medicine.

1.2 Classification of mixtures

2. Solutions and Solubility

2.1 Concentration of a solution

• Definition: amount of solute present in a specified amount of solvent or solution.
• Proportion control is essential when preparing solutions for intended effects.

2.2 Ways to express concentration

• % m/m and % w/w are numerically equal and used interchangeably.

2.3 Solubility

• Solubility property: maximum amount of solute that dissolves in 100 mL (or 100 g) of solvent at a given temperature.
• Solubility of most solids in liquids increases with temperature.
• Solubility of gases in liquids decreases with increase in temperature.
• Solubility curve: graph of solubility versus temperature.

3. Separation Methods for Homogeneous Mixtures

3.1 Crystallization

• Definition: formation of solid crystals from a saturated solution.
• Principle: difference in solubility at different temperatures.
• Steps: prepare hot saturated solution; filter hot solution; cool filtrate slowly; collect formed crystals.
• Use: separate and purify solids soluble in same solvent when solubility changes with temperature.
• Tip: slow cooling yields larger, well-formed crystals; rapid cooling yields smaller crystals.

3.2 Distillation

• Process: heat mixture; vaporise lower boiling component; condense vapour to recover liquid.
• Applicability: separates miscible liquids differing substantially in boiling point (≥25°C) or recovers solvent from solution.
• Fractional distillation: used when boiling points differ by small amounts (<25°c); separates="" multiple="" components="" by="" repeated="" vaporisation-condensation="">
• Industrial use: fractional distillation applied in petroleum refining to separate crude oil fractions.

3.3 Paper chromatography

• Method: solvent moves up paper carrying mixture components at different rates, producing separation into spots.
• Principle: differential affinity of components for mobile phase (solvent) versus stationary phase (paper).
• Etymology: chroma (colour) + graphein (to write).

4. Separation Methods for Heterogeneous Mixtures and Related Materials

4.1 Separation of two immiscible liquids

• Tool: separating funnel.
• Principle: difference in density; denser liquid forms lower layer and can be drained off first.
• Method: allow layer formation; open stopcock to collect lower layer; separate upper layer thereafter.

4.2 Sublimation

• Definition (term appears in Key Terms): solid converts directly to vapour on heating and vapour deposits back to solid on cooling.
• Use: separate a sublimable solid from a non-sublimable solid.

4.3 Alloys

• Alloy property: homogeneous mixture of metals or metal and non-metal.
• Physical methods cannot separate alloy components.

4.4 Suspensions and separation techniques

• Suspension property: contains solid particles dispersed in liquid that settle on standing and can be separated by filtration.
• Particle size criterion: particles larger than 1000 nm.
• Centrifugation: high-speed spinning forces heavier particles outward to separate solids from liquids.
• Coagulation: addition of a coagulant causes fine suspended particles to aggregate and settle for removal by sedimentation or filtration.

4.5 Colloids and emulsions

• Colloid property: particle size range 1-1000 nm; particles remain dispersed and do not settle.
• Filtration: colloidal particles cannot be separated by ordinary filtration.
• Tyndall effect observed for colloids (see Section 5).
• Components: dispersed phase and dispersion medium.
• Emulsion: colloid in which dispersed phase and dispersion medium are both liquids.

5. Tyndall Effect

5.1 Definition and occurrence

• Definition: scattering of light by particles in a colloid or suspension, making the light path visible.
• Occurrence: observed in colloids and suspensions; not observed in true solutions.
• Named after: John Tyndall.

6. Quick Summary: Separation Methods (Condensed)

6.1 Method - Principle

• Crystallization - difference in solubility at different temperatures.
• Distillation - difference in boiling points; recover lower-boiling component by vaporisation and condensation.
• Fractional distillation - repeated vaporisation-condensation for components with small boiling-point differences.
• Paper chromatography - differential movement rates on paper due to varied affinities.
• Separating funnel - density difference separates immiscible liquids into layers.
• Sublimation - one solid sublimes while the other does not.
• Centrifugation - centrifugal force separates components by density.
• Coagulation - coagulant induces particle aggregation leading to sedimentation.

7. Key Terms to Remember