The properties of Suspensions and Colloids
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
- A heterogeneous mixture
- The diameter of its particles is larger than 1000 nm .
- The suspended particles precipitate , if it is left for a short time without shaking .
- The suspended particles can be be seen by the naked .
- 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 .
Properties of Colloids
- A heterogeneous mixture ( apparently homogeneous ) .
- The diameter of the dispersed particles is 1 – 1000 nm .
- The dispersed particles do not precipitate , if they are left for a short time without shaking .
- The dispersed particles can be seen by the electron microscope only .
- The dispersed particles can’t be separated by filtration .
- 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 ) .
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 :
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 .