Flashcards
Chemical purity
Cards in this deck (15)
- 1What is meant by purity?When there is only one substance present
- 2Why is purity important?Impurities in food substances or medical drugs can have harmful effects on our health, thus, they must be pure. Computer chips also need to be made by very pure silicon or the chip will not work properly.
- 3How to know if a substance is pure?Pure substances have sharp melting and boiling points, where temperatures of them changing stage is distinct. Melting and boiling points will be affected when substances have impurities.
- 4How do impurities affect a substance's melting/boiling point?-The melting and boiling point is no longer sharp- it melts or boils in a narrow range, the range increasing with the increase of impurities
- The boiling point is increased- the more impurities, larger the increase
-The melting point is decreased- the more impurities, greater the decrease - 5How are mixtures purified?By methods of filtration, decanting and centrifugation. The solid is washed to remove any excess solution after separation. Evaporation of solvents can also be sued to separate a dissolved solid from a liquid.
- 6Describe the relationship between a solution, solute and solventA solution contains a solid dissolved in a solvent. The dissolved solid is called the solute. The liquid that dissolves the solid is the solvent.
- 7Describe filtrationAn undissolved solid is separated from a solution or liquid by passing it through a filter paper or funnel. The solution passed through is the filtrate, and the solid remaining on the filter paper is the residue. The solid is then washed to remove solution and dried in an oven.
- 8Describe decantingDecanting is simply pouring off the solution. It is suitable for very heavy particles, such as separating sand from water.
- 9Describe centrifugationA centrifuge is a machine which spins the test tubes around at a very high speed, The spinning pulls the solid to the bottom of the tube. You then decant the liquid from the solid. The purification can be repeated by washing and breaking up the solid and centrifuge it again.
- 10Desribe crystallisationCrystallisation is the obtaining of a crystalline solid from a solution. The solution is gently heated in an evaporating basin to concentrate it. The solvent is evaporated until the crystallisation point, where crystals form quickly, is reached. The concentrated solution is then left to cool, with crystals formed at the bottom. The crystals are then filtered and dried.
- 11Describe fractional crystallisationThis is used when two dissolved substances have different solubilities at different temperatures. A warm concentrated solution containing two solutes is cooled. The solute with lower solubility form crystals, the higher solubility solute remains in the solution. The insoluble solute is removed by filtration.
- 12Describe solvent extractionThis can be used to separate two solutes dissolved in a solvent. This is especially useful if one solute is volatile. A second solvent is used to extract one of the solids- make sure the two solvents are immiscible.
- 13What is the difference between fractional and simple distillation?Simple distillation is used to obtain a solvent from a solution while fractional distillation separates a mixture of liquids with different boiling points.
- 14Where can simple and fractional distillation be used?Simple distillation can be used to get drinking water from salt water on a large scale. Fractional distillation can separate petroleum fractions and ethanol form water.
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- IGCSE Chemistry (C2) Flashcards on Chemical purity, created by Maxine Gill on 23/05/2016.
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- Maxine Gill
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