Basic Concepts of Chemistry

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Basic Concepts of Chemistry : : Atoms and Molecules | Properties of Colloids

Chemistry is the branch of science which deals with the study of matter, its physical and chemical properties, the physical and chemical changes which it undergoes and the energy changes that accompany these processes.

Matter : Matter is anything that has mass and occupies space.

It can be changed from one form to another or into energy but can never be completely destroyed.

Elements of Chemistry

An element is a substance which can neither be broken nor built from two or more simple substances by any physical or chemical method.

Or in other words an element is a pure substance which contains only one kind of atom, e.g., Fe (Iron), Na (Sodium) etc.

Types of Chemistry Elements

  • Metals
  • Non – Metals
  • Metalloids

Compounds of Chemistry

A compound is a pure substance which contains more than one kind of element or atom in fixed proportion by weight e.g., NaCl (Sodium chloride), SO2 (Sulphur dioxide), etc.

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Types of Chemistry Compounds

  • Organic Compounds
  • Inorganic Compounds

The properties of a compound are completely different from those of its constituents.

Mixtures in Chemistry

A material containing two or more elements or compounds in any proportion is a mixture. It can be separated into its constituents, e.g., Air, Milk, Paints, Cements etc.

Types of Mixtures in Chemistry

Homogeneous : A mixture is said to be homogeneous if its composition is uniform throughout.
Heterogeneous : A mixture is said to be heterogeneous if its composition is not uniform.

The properties of a mixture are the properties of its constituents. A mixture with definite boiling point is known as azeotropic mixture.

Separation of Mixtures in Chemistry

  • Sublimation : In this process, a solid substance passes directly into its vapours on application of heat, and when vapours are cooled, they give back the original substance, e.g., iodine, napthalene, benzoic acid etc.
  • Sedimentation and Decantation : This method is used when one component is liquid and the other is insoluble solid.
  • Crystallization : This method is based on the difference in solubility of the various compounds in a solvent, e.g., mixture of KNO3 and NaCl can be separated by this process.
  • Filtration : It is used for quick and complete removal of solid suspended particles from a liquid (or gas) by passing the suspension through a filter.
  • Evaporation : In this method the solution is heated so that the solvent vaporises to give the solute (solid substance) e.g., salt can be obtained from salt solution.
  • Distillation : A mixture of two substances, only one of which is volatile, can be separated by this process, e.g., NaCl can be separated from water by distillation.
  • Fractional Distillation : This process is used if both the components of a mixture are volatile. It is based on the difference of boiling points, e.g., the various fractions of crude petroleum can be separated by this process.
  • Steam distillation : It is used to separate a liquid (should be immiscible with water) from a mixture by heating with steam, e.g., lemon oil, toluene, nitrobenzene etc.
  • Mechanical Separation : Two immiscible liquids can be separated by using a separatory funnel e.g., oil and water.
  • Magnetic Separation : Two solids one of which is magnetic substance can be separated by this method.
  • Atmolysis : In this process a mixture of gases can be separated based on their rates of diffusion, e.g., Isotopes of uranium (U235 and U238) are separated by converting them into gaseous UF6.
  • Chromatography : This is the most versatile separation method which can be applied to solid, liquid or gas. In this method the components of a mixture are adsorbed on a suitable adsorbent at different rates and thus get separated, e.g., to separate coloured materials from dyes, green vegetables, ink etc.

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