Explain the following observations:
(a) Lyophilic colloids are more stable than lyophobic colloid.
(b) Coagulation takes place when sodium chloride solution is added to a colloidal solution of ferric hydroxide.
(c) Sky appears blue in colour.

Answer:

a) Particles of dispersed phase have great affinity for the dispersion medium. They are self stabilised because of strong attractive forces operating between the suspended particles and the dispersion medium. e.g. gums gelatin.

b) When freshly precipitate Fe(OH)₃ is shaken with little amount of dilute solution of FeCl₃ (electrolyte)
Peptization process takes place by converting the Fe(OH)₃ precipitate into colloidal solution positively charged solution of Fe(OH)₃.

c)  Transmitted light is made up of a spectrum of colors the longest wavelength of light are on red end of spectrum and the shortest wavelength areon the blue/ violet end of the spectrum.
When transmitted light such as sunlight enters ours atmosphere it colloide with dust and water droplet and scattered violet/blue light.
But because our eyes are more sensitive to blue color thus we see blue color of sky.