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Methods of Separating Mixtures - Year 11 Chemistry
Transcript of Methods of Separating Mixtures - Year 11 Chemistry
Identify and describe procedures that can be used to separate naturally occurring mixtures of:
Solids of different sizes.
Solids and liquids.
Dissolved solids in liquids.
Assess separation techniques for their suitability in separating examples of earth materials, identifying the differences in properties which enable these separations.
Why 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 etc.
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.
Properties?? A property is a characteristic or feature of something. They can be physical or chemical. Physical Properties A physical property is a property of the substance by itself:
•Density (mass per unit volume)
•Melting Point (temperature at which a substances changes from solid to liquid)
•Boiling Point (temperature at which a substance changes from liquid to gas).
•Solubility (does the solute dissolve in a solvent to form a solution)
A chemical property is a proerty of the substance reacting with another chemical When separating mixtures, we need to identify which type of properties? PHYSICAL Solids of different sizes SIEVING – Small particles fall through the sieve and larger particles are caught. e.g. separating sand from gravel to make concrete. D.I.P = Paticle Size Solid suspended in a liquid Suspension: 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 mix with water FILTRATION – The liquid or solution passes through the paper while the suspended solid remains on top of the filter paper. D.I.P= Particle Size SEDIMENTATION followed by DECANTING – Once the solids settle to the bottom, the liquid is carefully poured off leaving the solid undisturbed. D.I.P = Density NOTE: mixtures of solids can be separated based on their SOLUBILITY – one solid is soluble (dissolves) in a solvent while the other is insoluble (doesn’t dissolve) e.g sand and salt. Dissolved solids in liquids Solution: A solid dissolved in a liquid Solute: Dissolved solid Solvent: Liquid that dissolves the solid Example: Saltwater solution. Solute? Solvent? The solute and solvent particles are similar in size. EVAPORATION –To collect the solid solute. The solvent (liquid) is vaporised (liquid to ?) D.I.P?? 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. Distillate: the liquid collected from the distillation D.I.P?? Miscible Liquids Miscible – 2 liquids dissolved in each other Examples: alcohol and water; oil in petrol DISTILLATION – used when there is a large difference in boiling points. The more volatile is vaporised, condensed becoming the distillate. The liquid with the lower boiling point FRACTIONAL DISTILLATION – separates liquids with small differences in boiling points using a fractionating column. Immiscible Liquids Immiscible - 2 liquids do not mix (oil and water) SEPARATING FUNNEL – Pear shaped funnel tapers to a narrow tube with a stopcock allowing the denser liquid to be collected. D.I.P = Different densities Gases FRACTIONAL DISTILLATION – air is liquefied by cooling then gradually heated in a fractional column to be collected separately. D.I.P?