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Pure and Impure Substances |
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All matter can be broadly divided into two major groups "Pure" and "Impure". The term 'purity' has quite a different meaning in chemistry than in our day-to-day life. Normally when we refer to pure water, pure milk, etc., what is implied is that the water, milk etc., are free from harmful substances such as bacteria, fungi, viruses, etc. 'Purity' in chemistry is entirely of a different nature. When we say a substance is pure, it means that the substance is made of only one type of constituent particles. |
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Pure Substances |
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A pure substance is homogeneous, irrespective of its origin or method of preparation, and it consists of only one kind of particles e.g. hydrogen, oxygen, water, sodium chloride, etc. |
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Elements |
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An element is a pure substance which is made up of only one kind of atoms having the same atomic number. |
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Compounds |
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A compound is a pure substance that is formed by the combination of atoms of two or more elements. The atom in a compound is chemically combined in a fixed and constant proportion. |
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Impure Substances - Mixtures |
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The constituents of a mixture may be elements, compounds, or both. These substances may be present in any proportion and exhibit their individual properties. |
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Distinction Between Compound and Mixture |
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Separation of the Constituents of Mixtures - Sedimentation and Decantation |
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The separation of the various constituents of different mixtures depends on the properties of the constituents. Some of these properties are size, density, magnetic nature of particles, solubility, miscibility, differences in boiling and melting points, sublimability, diffusibility and absorbance. |
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Separation of the Constituents of Mixtures - Filtration |
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Filtration is the process of separating the solid from liquids by passing through a filter. |
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Separation of the Constituents of Mixtures - Evaporation |
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The process by which a soluble solid can be obtained from a solution by allowing the solvent to vaporize, is called evaporation. |
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Separation of the Constituents of Mixtures - Distillation |
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Distillation is a method used to separate a solute and a solvent from a solution. In evaporation, vaporization takes place and only the solute is obtained. However, distillation is actually a combined process of vaporization and condensation. In distillation, both the solvent and solid are separated and collected from the solution of a soluble solid. Firstly, the solvent is vaporized by boiling it, and the vapour obtained is cooled. When it condenses to from the distillate, the solute is left behind. |
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Separation of the Constituents of Mixtures - Use of Separating Funnel |
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Liquids that are immiscible in each other differ in their densities and so can be separated by making use of a separating funnel. |
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Separation of the Constituents of Mixtures - Sublimation |
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Sublimation is a direct change from the solid state to gaseous state, without passing through the liquid state. If a mixture contains two solids, one sublimable, and the other non-sublimable, they can be separated by the process of sublimation. The solid that sublimes, escapes in the form of vapours. When these vapours are collected on a cold surface, they condense to form the sublimable solid, known as the sublimate. |
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Separation of the Constituents of Mixtures - Chromatography |
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Chromatography is a method of separating and identifying various components in a mixture, which are present in small trace quantities. There are several types of chromatography, one of which is paper chromatography. It is extensively used in research and industry, to analyse and identify different dyes. In its simplest form, it can be used to separate and identify the different dyes in black ink. |
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Separation of the Constituents of Mixtures - Crystallization |
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Crystallisation is the process by which crystals are obtained from a saturated solution of a substance, by allowing the solvent to evaporate slowly. If there are any insoluble impurities in the solution, they can be removed by filtration. Then by slow evaporation pure crystals can be obtained. |
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Separation of the Constituents of Some Common Mixtures |
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Mud and water
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Summary |
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Pure substances are made up of only one type of constituent particles. They are homogenous and have a definite set of properties characteristic of themselves. |
