The properties of Suspensions and Colloids

Suspensions

It is a heterogeneous mixture in which the diameter of its particles is larger than 1000 nm and it can be distinguished by the naked eye , such as the sand in the water and Chalk’s powder in the water .

Properties of Suspensions

  1. A heterogeneous mixture 
  2. The diameter of its particles is larger than 1000 nm .
  3. The suspended particles precipitate , if it is left for a short time without shaking .
  4. The suspended particles can be be seen by the naked .
  5. The suspended particles can be separated by filtration because filter paper ( ultra filtration membrane ) can hold the suspended particles , while the water passes through it .

Colloids

It is a heterogeneous mixture in which the diameter of its dispersed particles ranges between 1 : 1000 nm and it can be distinguished by the electron microscope .

Properties of Colloids

  1. A heterogeneous mixture ( apparently homogeneous ) .
  2. The diameter of the dispersed particles is 1 – 1000 nm .
  3. The dispersed particles do not precipitate , if they are left for a short time without shaking .
  4. The dispersed particles can be seen by the electron microscope only .
  5. The dispersed particles can’t be separated by filtration .
  6. The shape depends on its concentration : Concentrated colloids appear as milk or clouds , Diluted colloids appear clear .

The colloid is an intermediate case between the solution and the suspension because the diameter of colloid particles is in the range 1 : 1000 nm , which is smaller than that of suspension ( > 1000 nm ) and larger than that of solution ( < 1 nm ) .

Colloids

Colloids

How can you distinguish between the colloid and the true solution ?

By allowing a beam of light from a lamp to fall on each one , The colloid scatters the light because the size of the colloid particles is large enough , this phenomenon is known as Tendal’s phenomenon .

The colloidal systems

They consist of Dispersed phase and Dispersed medium

Dispersed phase ( like the solute in the solution ) , It is the substance that forms the colloidal particles .

Dispersed medium ( like the solvent in the solution ) , It is the medium in which the colloidal particles are dispersed .

Classification of colloidal systems according to the state :

Classification of colloids

Classification of colloids

There is no gas-gas colloidal system because mixed gases are homogeneous mixtures , whereas the colloid is a heterogeneous mixture .

When an amount of egg white is whipped by an electric mixture , A colloidal system ( gas in liquid type ) is formed .

Preparation methods of Colloids

There are two methods which are Dispersion method and Condensation method .

Dispersion method : The substance is crushed into small particles until its diameter reaches between ( 1 : 1000 nm ) , then added to the dispersed medium with stirring such as starch in hot water and cappuccino coffee .

Condensation method : The small particles are collected together into larger particles have the same volume of the colloid particles , by some processes like Hydrolysis , Oxidation – reduction .

Such as in the reaction of hydrogen sulphide with sulphur dioxide , where the atoms of sulphur in the water form colloid .

Sugar dissolves in the water forming a solution , but milk powder disperses in the water forming a colloid because the size particles of sugar after dissolving is 1 nm , but that in case of milk powder ranges between 1 : 1000 nm .

Chalk’s powder forms a suspension in the water because the size of chalk’s particles is > 1000 nm .

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