0QUESTION
Nitric oxide becomes brown when released in air.
ANSWER
(i) Nitric oxide combines with oxygen when exposed to air to give nitrogen dioxide which is brown in colour.
(ii) Bi has little tendency to form pentahalides because + 5 oxidation state of Bi is much less stable than + 3 oxidation state due to inert pair effect.
QUESTION
Give reasons for the following observations:
(i) Leather gets hardened after tanning.
(ii) Lyophilic sol is more stable than lyophobic sol.
ANSWER
(i) The process of hardening of leather is known as tanning. Tannin, which is obtained from a mixture of polyhydroxy benzoic acids and contains negatively charged colloidal particles. Animal skin is colloidal in nature and has positively charged particles. When they are soaked in tannin, their mutual coagulation takes place and, thus leather becomes hard after tanning.
(ii) Lyophilic sols are more stable than lyophobic sols. This is due to the fact that lyophilic colloids are extensively solvated, i.e. colloidal particles are covered by a sheath of the liquid in which they are dispersed.
