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Solutions, suspensions and colloids


SOLUTIONS, SUSPENSIONS AND COLLOIDS


  • A Solution can be defined as a homogenous mixture of two or more non-reacting substances whose composition can also be varied within certain limits

 

Components of a Solution:

  • In a binary solution there are only two constituents or components. These are known as Solute and Solvent
  • The ‘substance which is dissolved’ in a liquid to make a solution is called solute, and the ‘liquid’ in which solute is dissolved is known as solvent.
  • The solute particles are also called ‘dispersed particles’ and solvent is also known as dispersion medium.
  • Solutions made by dissolving various solutes in water are called aqueous solutions.

 

Properties of Solution:

  • The important characteristic properties of a solution (or true solution) are as follows:
  • A solution is a homogeneous in nature which means that it has same composition through out.
  • All components or constituents in a solution are present in the same phase.
  • The size of solute particles in a solution is extremely small. It is less than 1 nm in diameter (1 nanometre = 10-9 metre).
  • The particles of a solution cannot be seen even with a microscope.
  • The particles of a solution are very small that they can even pass through the pores of even fine filter papers, so solute cannot be separated from the solvent by filtration.
  • The solutions are very stable. The particles of solute present in it do not settle down.
  •  A true solution does not scatter light (This is because its particles are very, very small).

 

SUSPENSIONS:

  • Those substances which are insoluble in water from suspensions.
  • A suspension may be defined as a defined as a heterogeneous mixture in which the solid particles are spread throughout the liquid without dissolving in it. They settle as precipitate if suspension is left for some time.
  • A suspension is a heterogeneous mixture in which the small particles of a solid are spread throughout a liquid without dissolving in it.
  • Chalk-water mixture, muddy water, milk of magnesia, sand particles suspended in water, and flour in water.

 

Properties of a Suspension:

  • The important characteristic properties of a suspension are given below:
  • A suspension is a heterogeneous mixture.
  • The size of solute particles in a suspension is quite large. It is larger than 100 nm in diameter.
  • The particles of a suspension can be seen easily.
  • The particles of a suspension do not pass through a filter paper. So, a suspension can be separated by filtration.
  • The suspensions are unstable. The particles of a suspension settle down after some time.
  • A suspension scatters a beam of light passing through it (because its particles are quite large).

 

COLLOIDS:

  • A colloid is a kind of solution in which the size of solute particle is intermediate between those in true solutions and those in suspensions.

Properties of Colloids:

  • The important characteristic properties of colloids (or colloidal solutions) are follows:
  • A colloid (or colloidal solution) appears to be homogeneous but actually it is heterogeneous.
  • The size of particles in a colloid (or colloidal solution) is bigger than those in a true solution but smaller than those in a suspension. It is between 1 nm and 100 nm in diameter.
  • The particles of most of the colloids (or colloidal solutions) cannot be seen even with a microscope.
  • The particles of a colloid (or colloidal solution) can pass through a filter paper. So, a colloid cannot be separated by filtration.
  • There are two phases in colloidal solution. They are known as dispersed phase and dispersion medium. The component present in smaller proportion is the dispersed phase while the one present in greater proportion is the dispersion medium.
  • The colloids (or colloidal solutions) are quite stable. The particles of a colloid do not separate out on keeping.
  • A colloid (or colloidal solution) scatters a beam of light passing through it (because its particles are fairly large).The particles present in a colloidal solution have size big enough to scatter or disperse the light rays present in the beam as they fall on them. As a result these rays as well as colloidal particles become visible. The scattering of light by colloidal particles is known as Tyndall effect. This effect is not observed in true solution as the size of particles in it is too small.
  • Depending upon the state of matter present in the dispersed phase and dispersion medium there are nine different types of colloidal solutions.

 

Common examples of colloids:

 

Sky appears blue:

  • There is no blue colour as such in the sky. Fine particles of dust etc. are always present in the atmosphere. When sun light falls on the particles, they scatter light with a blue colour or tinge. That is why sky appears blue.

 

Cleansing action of soap

  • Clothes become oily because of perspiration, when dust particles come in contact with the clothes they become dirty. Water cannot remove oil drops from the clothes. Soap helps in forming an emulsion between water and oil drops carrying dust. As a result, these are removed from clothes and they get washed.