Lower Secondary Science Separation Techniques Notes

Transcription

1 Lower Secondary Science Separation Techniques Notes 1. Ways of separating mixtures. Filtration Separates insoluble solid from liquid. Residue is collected at the filter and the liquid that filters through is the filtrate. Water treatment plant. Tea bags. Vacuum cleaners Nose, kidneys Funnel Filter Paper (folded) Residue Filtrate Evaporation Separates soluble solid from liquid. Use direct heating. Sometimes steam bath is used to limit heating temperature to prevent chemical reactions (e.g. decomposition) from taking place. Salt Solution Evaporating Dish Wire Gauze Beaker Water Tripod Stand Bunsen Burner Direct Heating Steam Bath Obtain salt from sea water. Produce powdered milk. Crystallization Obtains soluble solid from a solution. Separates a soluble solid that decomposes on heating. A very slow method of separation. Purpose: To obtain pure crystals. Production of sugar. Production of silicon wafers Production of blue copper sulfate crystals Crystal Solution Page 1 of 5

2 Magnetic Attraction Distillation To separate magnetic material (e.g. iron or steel) from non-magnetic material. Application: Junk yards. Mining Industry Cleaning up agricultural products Treatment of sewage Magnetic Material Magnet Thermometer Tap water out Solid Liquid (eg. Salt Water) Condenser Porcelain Chips Tap water in Distillation is used to separate mixture of solid-and-liquid or liquid-and-liquid. Liquids to be separated must have different boiling points. Distillation is a process which the liquid is heated to a gaseous state and it is cooled until it condenses as a pure liquid (collected in a separate flask) leaving the solid behind. Porcelain chips are added to the liquid mixture to ensure smooth boiling (poor conductor of heat thereby causing heat flow to be slower) Cold water running through the condenser will cool the vapour which will condense to a liquid. Fractional distillation is used to separate: a mixture of 2 or more liquids a liquid-liquid mixture that has very close boiling points Distillate (Pure Water) Page 2 of 5

3 Thermometer Tap water out Fractionating Column Condenser Miscible Liquids (eg. Alcohol and Water) Tap water in Porcelain Chips Distllate The fractional distillation setup is similar to the distillation setup except it has a fractionating column to help in separating the two liquids. Fractional distillation of crude oil to obtain petrol, diesel, kerosene, lubricating oils, etc. Distillation of sea water to get fresh water (this process is also called desalination) Dry cleaning Making alcoholic drinks/separate ethanol from water Oxygen and nitrogen gases from liquid air Oil Refining and Fractional Distillation - Crude oil is refined into products such as gasoline, asphalt, and waxes by a process called fractional distillation. During the process, the parts, or fractions, of crude oil are divided out successively by their increasing molecular weight. For instance, gasoline has a low molecular weight and vaporizes at a fairly low temperature. This means that at the appropriate temperature, while all of the rest of the oil is still in liquid form, gasoline may be separated out. The remaining oil goes through the same process at a slightly higher temperature, and jet fuel is divided out. Repeating the distillation process several times will separate out several constituents of crude oil, which are then processed and put to a wide range of uses. Page 3 of 5

4 Chromatography To separate mixture of liquids (usually coloured). Based on the principle that different components of the liquid mixture travel at different speed in another medium, eg paper. Separate the components of food colourings or dyes to test that they are safe for use. Urine/ Drug testing. Chromatogram Chromatogram Split Cork Boiling Tube Chromatography Paper Ink Spot Solvent Separating funnel To separate liquids that are immiscible, e.g. oil and water. The mixture is poured into the separating funnel. A tap at the bottom of the funnel allows the lower layer of liquid to be removed. Stopper Oil Water Tap Page 4 of 5

5 Sublimation To separate substances that sublimes upon heating from substances that do not. Heat the mixture until a solid sublimes, collect the vapour and cool it so that it condenses back into solid. Sublimed solid Reverse Osmosis Partially permeable membrane allows water molecules to pass through but not salt. Apply pressure on the side containing salt water so that water molecules passes through the membrane to the side containing pure water. Pressure Partially Permeable Membrane Pure Water Salt Water Page 5 of 5