Methods to Separate Mixtures

Syllabus Dot points:Identify and Describe procedures that can be used to separate naturally occurring mixtures of:Solids of different sizesSolids and liquidsDissolved solids in liquidsLiquidsGases

Assess separation techniques for their suitability in separating examples of earth materials, identifying the differences in properties which enable these separations

Methods to Separate MixturesWhy Separate?Most of the mixtures we extract from the Earth have to be separated into their components before we can use them.For example salt (sodium chloride) from water.Very few mixtures are used as they are: coal, sand for concrete and glass, sandstone, granite and other rocks for buildings.Since the different particles within a mixture are not all chemically bonded together, and since each has different properties, they can be separated fairly easily by simple physical processes.A property is a characteristic or feature of something. They can be physical or chemical.PropertiesPropertiesPhysical PropertiesA physical property is one that is displayed without any change in composition.DensityColourConductivityMalleabilityLusterChemical PropertiesAny characteristic that gives a sample of matter the ability/inability to undergo a change that alters its composition.ReactivityToxicityStabilityBond strength

Solids of different sizesSIEVING Small particles fall through the sieve and larger particles are caught. E.g. Separating sand from gravel to make concrete.

Solid suspended in liquidSuspension: is a dispersion of particles through a liquid with the particles being sufficiently large that they eventually settle on standing.The solid is INSOLUBLE (it does not dissolve in the liquid).Example: Sand mixed with waterNOTE: mixtures of solids can be separated based on their SOLUBILITY one solid is soluble (dissolves) in a solvent while the other is insoluble (doesnt dissolve) e.g. sand and salt.Solid suspended in liquidFILTRATION (Particle Size) The liquid or solution passes through the paper while the suspended solid remains on top of the filter paper

SEDIMENTATION followed by DECANTING (Density) Once the solids settle to the bottom, the liquid is carefully poured off leaving the solid undisturbed.

Dissolved solids in liquidsSolution: A solid dissolved in a liquidSolute: Dissolved solidSolvent: Liquid that dissolves the solidEVAPORATION To collect the solid solute. The solvent (liquid) is vaporised (liquid to gas)DISTILLATION To collect the liquid solvent. The solution is boiled with the vapour formed being condensed back to a liquid in a different part of the apparatus.

Miscible LiquidsMiscible 2 liquids dissolved in each otherExample: alcohol and water; oil in petrolDISTILLATION used when there is a large difference in boiling points. The more volatile is vaporised, condensed becoming the distillate. (the liquid with lower boiling point)FRACTIONAL DISTILLATION separates liquids with small differences in boiling points using a fractionating column.Immiscible LiquidsImmiscible 2 liquids do not mix (oil and water)SEPARATING FUNNEL (Different Densities) Pear shaped funnel tapers to a narrow tube with a cork allowing the denser liquid to be collectedGasesFRACTIONAL DISTILLATION Air is liquefied by cooling then gradually heated in a fractional column to be collected separately.