Colloid explain abd give example
Answers
Answer:
Definition: A colloid is a substance microscopically dispersed evenly throughout another substance. The dispersed-phase particles have a diameter between about 5 and 200 nanometers. Examples: Milk is an emulsion, which is a colloid in which both parties are liquids
Answer:
In simple terms, we can define colloids as a mixture where one of the substances is split into very minute particles which are dispersed throughout a second substance. The minute particles are known as colloidal particles.
Alternatively, we can also say that colloids are basically solutions in which solute particle size ranges from 1nm – 1000 nm. Colloids are heterogeneous in nature.
a) by oxidation
Colloidal sulphur can be obtained by passing oxygen gas through a solution of hydrogen sulphides. In this method any oxidising agent like HNO3, H3Br2 can also be used.
2H2S + O2 → 2H2O + 2S (Sulphur sol)
b) By double decomposition:
A solution of arsenic sulphide is obtained in this method. In this process hydrogen sulphide is passed through Arsenious oxide cold solution in water.
AS2O3 + 3H2S → AS2S3 + 3H2O Arsenic sulphide (sol)
c) By reduction:
A number of metals such as gold, silver, and platinum are obtained in a colloidal state by reacting the aqueous solution of these salts with suitable reducing agents such as formaldehyde, phenylhydrazine, hydrogen peroxide, stannous chloride etc.
2AuCl3 + 3SnCl2 → 3SnCl4 + 2Au (gold sol)
2AuCl3 + 3HCHO + 3H2O → 2Au + 3HCOOH + 6HCl
The gold sol prepared in the reduction of gold chloride solution has a purple colour and is called purple of Cassius.
d) By hydrolysis:
Many salt solutions are rapidly hydrolysed by boiling a dilute solution of their salts. For example, ferric hydroxide and aluminium hydroxide sols are obtained by boiling solutions of the corresponding chloride.
FeCl3 + 3H2O → Fe(OH)3 + 3HCl colloidal sol
Silicic acid sol is obtained by the hydrolysis by sodium silicate.
e) By double decomposition:
A sol of arsenic sulphide is obtained in this method. In this process hydrogen sulphide is passed through Arsenious oxide cold solution in water.
As2O3 + 3H2S → As2 S3 + 3H2O Arsenic sulphide (sol)
f) By excessive cooling:
A colloidal sol of ice is obtained in this process. Ice is taken in an organic solvent like chloroform ether. Sol of ice is obtained by freezing a solution of water in the solvent. The molecules of water are no longer in the solution separately combine to form particles of colloidal size.
h) By exchange of solvent:
In this process, colloidal sol of certain substances such as sulphur, phosphorus which are soluble in alcohol but insoluble in water can be prepared by pouring their alcoholic solution into water. For enough alcoholic solution of sulphur on pouring into water gives a milky colloidal solution of sulphur.
i) By change of physical state:
Sols of substance like mercury and sulphur are prepared by passing the vapour through cold water containing a suitable stabilizer such as ammonium salt or citrate.