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Important Terms and Their Definitions

Intermolecular forces: These are the forces of attraction that operate among the constituent particles (atoms, molecules or ions) of a matter.
Diffusion: It is the mixing of one gas with another. If the average kinetic energy of different types of molecules (different masses) is same, which are at thermal equilibrium is the same, then their average velocities are different.
Element: An element is a pure substance which cannot be split up into two or more simpler substances by any physical or chemical means. It is the simplest form of matter.


Metals: Copper, zinc, aluminium
Non-metals: Hydrogen, oxygen, chlorine, nitrogen
Metalloid: Boron, silicon, arsenic


Atomicity: It is the number of atoms present in a molecule.
Monoatomic: When only one atom is present in a molecule, it is said to be monoatomic, e.g. He, Ne, Cu, Ar etc.
Diatomic: When only two atoms are present in a molecule, it is said to be diatomic, e.g. O2, N2, H2 etc.
Polyatomic: When many atoms are present in a molecule, it is said to be polyatomic, e.g. S8, P4, O3 etc.
Compound: A compound is a pure substance formed from two or more elements combined together in a definite proportion by mass, e.g. NH4Cl, H2O, CO2, CaCO3 etc.
The properties of a compound differ entirely from those of its constituent elements.
Mixture: A mixture is a substance containing two or more pure substances in close contact and mixed together in any proportion in which each substance retains its own composition and properties.
Based on the composition, mixture is of two types:
Homogeneous mixture: It is a mixture of two miscible liquids in which different constituents are mixed uniformly. For example, air, sea water, sugar solution.
All solutions are homogenous.
Heterogeneous mixture: It is a mixture of two immiscible liquids or two solids in which various constituents are not mixed uniformly. Table 1.1 shows the classification of heterogeneous mixture.


mixture of oil + water, iron fillings + sulphur powder
All suspensions are heterogeneous.


Classification of Heterogeneous Mixture
Types Examples
Solid–solid mixture Sugar and salt
Solid–liquid mixture Sand and water
Solid–gas mixture Air trapped in the pores of soil particles
Liquid–gas mixture Oxygen in contact with water
Gas–gas mixtur Hydrogen and oxygen
Liquid–liquid mixture Water and oil
Alloys: An alloy is a homogeneous mixture of (a) two or more metals or (b) metals and non-metals. Different types of alloys and their respective components and uses are given in Table 1.2 through Table 1.6.
A mixture of two or more substances can be a solution, a suspension or a colloid.
Alloys of Copper, Their Components and Uses
Alloy Components Uses
Brass Copper and zinc Utensils, electrical appliances
Bronze Copper and tin Statues, bells, coins and utensils
German silver Copper, zinc and nickel Utensils, resistance coils, ornamental wares
Gun metal Copper, tin and zinc Barrels of guns, gears and castings
Alloys of Iron, Their Components and Uses
Alloy Components Uses
Stainless steel Iron, carbon, nickel and chromium Surgical instruments, utensils
Nickel steel Iron and nickel Utensils, drilling instruments
Alnico Iron, nickel, aluminium and cobalt In making magnets
Invar steel Iron, nickel and carbon In making pendulums
Nichrome Iron, nickel and chromium Heating coils
Steel Iron and carbon Pipes, nails, sheets and cutting tools


Alloys of Aluminium, Their Components and Uses
Alloy Components Uses
Alnico Aluminium, nickel cobalt and iron Permanent magnet
Duralumin Aluminium, copper, manganese and magnesium Pistons and rotating aircraft engine parts
Magnalium Aluminium, magnesium, copper, nickel and ti Airplane bodies, ladders etc.


Alloys of Lead, Their Components and Uses
Alloy Components Uses
Solder Lead and tin Printed circuit boards use solder joints to mount components and create a circuit
Typemetal Lead, antimony and tin Type founding and hot metal type setting
Alloys of Nickel, Their Components and Uses
Alloy Components Uses
Alumel Nickel, manganese, aluminium and silicon Thermocouples
Chromel Nickel and chromium Thermocouples
Cupronickel Nickel, copper, iron and manganese Propellers, crankshafts and hulls of premium tugboats
Monel metal Nickel, copper and iron Musical instruments such as trumpets, electric bass strings etc.
Solution: A solution is a homogeneous, molecular mixture of two or more substances.
A solution contains two components:
  1. Solvent: The liquid in which a substance is dissolved (medium of dispersion) is called a solvent.
  2. Solute: The substance which is dissolved in a solvent to produce a solution is called a solute particle.
In general, the substance present in smaller proportion in a solution is called the solute, whereas the one present in greater proportion is called the solvent.
Aqueous solution: It is a solution produced by dissolving a substance in water, e.g. NaCl in water, CuSO4 in water etc.
Non-aqueous solution: When solutions are obtained by dissolving a solute in liquids other than water such as alcohol, acetone, carbon tetrachloride and carbon disulphide, then it is called as non-aqueous solution. For example, I2 dissolved in CCl4.
Universal solvent: Water being polar in nature dissolves more substances than any other solvent. Hence it is known as the universal solvent.
True solution: When the solute particles are dispersed between the particles of the solvent, it is called a true solution.
Depending on the amount of solute dissolved, solutions can be divided into two classes as shown in Figure 1.3.
Solubility: The amount in grams of a solute dissolved in 100 grams of a solvent to make a saturated solution is called the solubility of the solute in the given solvent at a given temperature and pressure of the solution.
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  • The solubility of gases in liquids decreases with rise in temperature, but increases with increase in pressure.
  • The solubility of solids in liquids generally increases with rise in temperature, but hardly changes with change in pressure.
  • When a solute is added to a solvent, its freezing point decreases and boiling point increases.


Suspension: It is a heterogeneous mixture in which small particles of a solid do not dissolve but remain suspended throughout the mass of the liquid or gas.
The size (diameter) of the particle is of the order of 10–5 cm or larger.
Colloid: It is a heterogeneous solution in which the size of the solute particles lies between that of particles in a true solution and that of those in a suspension. It ranges from 10–7 to 10–5 cm. They show the following effects:
  1. Brownian movement: Colloidal particles are in a state of constant and rapid zig-zag motion called Brownian movement. It arises due to collisions of colloidal particles with molecules of the solvent.
  2. Tyndall effect: The scattering of light by colloidal particles is called Tyndall effect.
  3. Electrophoresis: The colloidal particles are electrically charged. Under applied electric field, the colloidal particles move towards an electrode.
The movement of charged colloidal particles under the influence of an electric field is known as electrophoresis. It is used to study the mixtures of proteins, enzymes etc.
Separation of components of a mixture:
Solid–solid Solid–liquid Liquid–liquid
(i) Sublimation
(ii) Magnetic separation
(iii) Solvent extraction
(iv) Winnowing
(i) Filtration
(ii) Sedimentation
(iii) Evaporation
(iv) Distillation
(v) Centrifugation
(i) Separating funnel
(ii) Fractional distillation

 This method is used to separate a sublimable solid from a non-sublimable solid, e.g. separation of a mixture of salt and iodine.
Magnetic separation: This method is used to separate a magnetic solid from a non-magnetic solid, e.g. separation of iron filings from sulphur.
Solvent extraction: This method is used to separate a solid which is soluble in a solvent from an insoluble solid, e.g. separation of sulphur from charcoal.
Winnowing: This method is used to separate lighter particles from heavier particles by blowing air by the force of wind, e.g. separation of paddy from husk.
Filtration: This method is used to separate the mixture of insoluble solid from a liquid, e.g. separation of chalk from water.
Sedimentation: This method is used to separate the mixture of insoluble solid (but settles down) from a liquid, e.g. separation of sand from water.
Evaporation: This method is used to separate a mixture of a soluble solid from a liquid, e.g. separation of common salt from water.
Distillation: This method is used to separate a mixture of soluble liquid components having different boiling points, e.g. separation of benzene from toluene.
Centrifugation (separation of particles of different densities): This method is used to separate immiscible liquids or solids from liquids by the application of centrifugal force. The separation proceeds slowly by gravity and hence can be speeded up enormously in centrifugal equipment, e.g. separation of cream from milk, separation of sugar crystals from molases.
Chromatography: Used to separate components of a mixture which exhibits nearly the same chemical properties and present in trace amounts. It is based on the principle that components of a mixture get separated due to difference in adsorbtion on an adsorbent, e.g. f-block element are separated by this method.
Separating funnel: It is a method to separate a mixture of immiscible heavier liquid from an immiscible lighter liquid, e.g. separation of water and oil.
Fractional distillation: This method is used to separate a mixture of miscible liquids with different boiling points, e.g. separation of methyl alcohol and water.

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