Solved Examples on Surface Chemistry: 

Question: 1 Rate of physisorption increases with                (IIT JEE 2003)

a) decrease in temperature

b) increase in temperature

c) decrease in pressure

d) decrease in surface area 

Answer: a 

Solution:In physisorption, adsorbate is held on the surface of adsorbent by van der Waals forces only. The attraction between surface of adsorbent and the absorbate particles decreases with increase in temperature and vice versa.

Hence, the correct option is A.

Question:2 Among the following, the surfactant that will form micelles in aqueous solution at lowest molar concentration at ambient condition is-         (IIT JEE 2008) 

a) CH₃(CH₂)₁₅N(CH₃)₃Br

b) CH₃(CH₂)₁₁OSO₃Na

c) CH₃(CH₂)₆COONa

d) CH₃(CH₂)₁₁N(CH₃)₃Br

Answer: a

Solution: Critical concentration for micelle formation decreases as the molecular weight of hydrocarbon chain of surfactant grows because in this case true solubility diminishes and the tendency of surfactant molecules to associate increases.

Hence, the correct option is A.

Question: 3 Which of the following electrolytes is most effective coagulating agent for Sb₂S₃?  (IIT JEE 2009S)

a) Na₂SO₄

b) CaCl₂

c) Al₂(SO₄)₃

d) NH₄Cl

Answer: c

Solution: As Sb₂S₃ is a negative sol, so will be the most effective coagulating agent due to higher positive charge at Al (Al³⁺).

Hence, the correct option is C.