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Separation of mixtures. Substances are mixed physically in a mixture. Element is a pure substance made up of only one kind of atoms. E.g. Sodium, Hydrogen, carbon
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Separation of mixtures Substances are mixed physically in a mixture
Element is a pure substance made up of only one kind of atoms. E.g. Sodium, Hydrogen, carbon • Compound is a pure substance made up of two or more elements combined chemically. E.g. water, alcohol, carbon dioxide, copper sulphate • Mixture is an impure substance consists of two or more substances mixed physically. E.g. Air, mud water, petrol, milk
Magnetic separation If one of the substances in the mixture is magnetic, we can separate it by using a powerful magnet. Eg: iron from a mixture of iron and sulphur
Filtration • If the solid does not dissolve in the solvent, we can filter the solid out by filtration • Chalk powder from a mixture of chalk powder and water
Decantation • A method to separate an insoluble solid from a mixture Eg: Mud from a mixture of mud and water
Separating funnel If two liquids are immiscible, they can be separated by using a separating funnel Eg. Oil and Water
Evaporation • If a solute is completely soluble in a solvent, evaporate the solvent to get the solute. (make sure that the solute does change on heating) • Evaporation is done in an evaporating dish. Eg: salt from salt solution.
Crystallisation • If the solute is dissolved in a solvent, we can get the pure solute by this method. • Sometimes the solute decomposes or evaporates water of crystallisation on complete drying. • A saturated solution is heated until point of crystallisation and then cooled. • Crystals will be formed at the walls of the container. Eg: Copper sulphate from copper sulphate solution.
Centrifugation This method is useful to separate a solid in a suspension The solid particles settle at the bottom of the test tube when it spins
Sublimation • Substances changes to gaseous state without passing through a liquid state is called sublimation. • If substance which slows sublimation is present in a mixture, we can separate it by this method. • Eg: Iodine from a mixture of iodine and sand
Distillation • This method is useful to separate a solvent from a solution. • A condenser is used in simple distillation • Eg: Water from salt solution
Fractional distillation • This method is used to separate two miscible liquids from their mixture. • Fractional distillation is done based on Boiling Points. • Eg: Alcohol and water from their mixture
Chromatography • This method of separation is used to see what coloured materials make up e.g. a food dye analysis. • The material to be separated e.g. a food dye (6) is dissolved in a solvent and carefully spotted onto chromatography paper. Allow a suitable solvent to run • Alongside it are spotted known colours on a 'start line' (1-5).
In chromatography there is a stationary phase and a mobile phase. • Mobile phase takes different components to different parts of the stationary phase. • The distance travelled by the components depends on the solubility of the component. • If the component is white, it is not visible. Then spray a chemical(like ninhydrin) over the paper so that the component will be visible. • Such chemicals used to make the components are called locating agents.
Chromatography can be used to identify the components in a mixture too. • Put several drops of the mixture on the base line. Put drops of suspected components also on the line. • Run the solvent. • See the components ran equal to the suspected ones. • In the chromatography on the right side, mixture M contains B, C, and D and not A
Another way to identify the components in a mixture is by calculating Rf values. • Each substance has a definite Rf value which you can find in reference sources. • Conduct the chromatography and calculate the Rf value for each component by the following method: • Rf= Distance travelled by the component Distance travelled by the solvent front • Compare the Rf value calculated with that of book value and identify the components.
Look at the chromatograph on right hand side. • Mixture M contains components A and B • Rf of A = 4.30 =0.26 16.80 • Rf of B = 10.20 =0.61 16.80 • Find which substances have the calculated Rf. • It means M contains these components.
