question_answer

  (a) Give one main difference between lyophilic and lyophobic colloids. (b) Explain. (i) Sky appears blue in colour. (ii) A freshly formed precipitate of ferric hydroxide can be converted to a colloidal sol by shaking it with a small quantity of ferric chloride.                                                                                                                                     [1+2]

Answer:

  (a)                           

Lyophilic colloids	Lyophobic colloids
Lyo-means liquid and philic-means loving (attracting). Thus, these colloids have strong interactions with the dispersion medium. These are stable and are also reversible colloids.	Lyo-means liquid and phobic means hating (liquid hating). These are sparing soluble in liquid and do not pass readily into colloidal state. Thus, they are less stable and irreversible.

[1] (b) (i) Sky appears blue in colour Dust particles along with water suspended in air scatter blue light which reaches our eyes (in visible range) and sky appears blue to us.   [1] (ii) When freshly prepared precipitate of is shaken with  there is adsorption of  ions on the surface. Thus, positively charged colloidal sol is formed.                                                           [1] Thus,