Give reasons for the following :
(a) Leather gets hardened after tannig
( b) `Fe Cl_3` is preferred over KCl in case of a cut leading to bleeding .

Explanation

Animal skin is colloida in nature and has positively charged partices ,whereas taninng consits of negatively charged colloidal particles .When animal skin is soaked in tanning mutual coagulation takes palce and as a result,leather gets hardened .
( b) This is because the valency of iron in ferric chloric is 3+ whereas that of potassium in KCL is 1+ The higer the better is the coagulation efficieny of the compond .Also ferric chloride is more compatible with skin than KCl.
( c) At high pressure `1/n=0` ,hence extent of adsorption becomes of pressure .