(General Science) CHEMISTRY - Solutions, Suspensions and Colloids

GENERAL SCIENCE: CHEMISTRY


General Science Note for IAS Exam

Solutions, Suspensions, and Colloids

The substance which dissolves in another substance to form a solution is called the solute, and the substance in which the solute dissolves is called the solvent. Solute particle can also be referred to as the ‘dispersed particles’ and solvent as the ‘dispersion medium’. The size of solute particles is minimum in solutions and maximum in suspensions. Solutions in which the solvent is water are called aqueous solutions and those in which the solvent is an organic liquid are called non-aqueous solutions.

Solutions


A solution is a homogeneous mixture. Examples: Salt solution, sugar solution, and soft drinks, vinegar, sea water, air and metal alloys like brass.

Important Characteristics of a Solution:

  • A solution is a homogenous mixture.
  • The solute particles are extremely small in size (less than 1nn in diameter). They cannot be seen even with a microscope.
  • The solute cannot be separated from the solvent by filtration.
  • A solution does not scatter light because the particles are extremely small.

Types of Solutions

  • Solid in solid: Metal alloys like brass (solution of zinc in copper), bronze (solution of tin in copper)
  • Solid in liquid : solution of sugar in water, copper sulphate in water
  • Liquid in liquid: Vinegar (solution of acetic acid in water)
  • Gas in liquid: Carbonated drinks like Coca- cola, soda-water
  • Gas in Gas: Air (solution of oxygen, carbon dioxide, argon, water vapour, etc., in nitrogen gas)

Suspensions


A suspension is a heterogeneous mixture in which particles of a solid are dispersed in the liquid without dissolving in it. Examples: Sand particles in water, mud in water, chalk particles in water, milk magnesia (magnesium hydroxide in water).

Important Characteristics of a Suspension:

  • A suspension is a heterogeneous mixture.
  • The solute particles in suspension are quite large (more than 100 nm in diameter).
  • The particles in a suspension can be seen easily.
  • The particles can be separated from the dispersion medium by filtration.
  • The particles of a suspension settle down on keeping.
  • As the particles are large, a suspension scatters the beam of light passing through it.

Colloids


A colloid is a type of solution in which the particle size of the solute is bigger than that of a true solution but smaller than that a suspension. Colloidal solutions are heterogeneous.
Examples:
Milk, blood, soap, starch solution, ink, jelly.

Important Characteristics of a Colloid:

  • A colloid is heterogeneous even thought it appears to be homogeneous.
  • The diameter of solute particles in a colloid is between 1nm and 100nm.
  • The particles of colloids cannot be seen even with a microscope.
  • A colloid can be separated by centrifugation but not by filtration.
  • The particles of a colloidal solution do not settle down on keeping.
  • A colloid scatters a beam light passing through it. Scattering of light by colloidal particles is known as Tyndall Effect.

Types of Colloids

Colloids can be classified into the following groups on the basis of the physical state of the dispersed phase medium:

  • Sol (tiny solid particles dispersed in a liquid). E.g. Soap solution. Starch solution, ink, paint
  • Solid sol (solid particles dispersed in a solid). E.g. Coloured gemstones like ruby, sapphire, emerald
  • Aerosol (a solid or liquid dispersed in a gas) E.g. Smoke, automobile exhausts, fog, mist, clouds, hairspray
  • Emulsion (small drops of a liquid dispersed in another liquid). E.g. Body lotion, milk butter
  • Foam (a gas dispersed in liquid). E.g. Shaving cream soap bubbles, fire-extinguisher foam
  • Solid foam (a gas dispersed in a solid). E.g. Sponge, bread, foam rubber
  • Gel (a network of solid particles dispersed in liquid). E.g. Gelatine, jelly, hair gel

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