Surface Chemistry

1

Which one of the following characteristics is not correct for physical adsorption?

  1. Both enthalpy and entropy of adsorption are negative.
  2. Adsorption is spontaneous.
  3. Adsorption increases with increase in temperature.
  4. Adsorption on solids is reversible.
2

3 g of activated charcoal was added to 50 mL of acetic acid solution (0.06 N) in a flask. After an hour it was filtered and the strength of the filtrate was found to be 0.042 N. The amount of acetic acid adsorbed (per gram of charcoal) is:

  1. 54 mg
  2. 42 mg
  3. 36 mg
  4. 18 mg
3

Which of the following statement is incorrect regarding physissorptions?

  1. It occurs because of van der Waal's forces.
  2. More easily liquiefiable gases are adsorbed readily.
  3. Enthalpy of adsorption (ΔHadsorption) is low and positive.
  4. Under high pressure it results into multi molecular layer on adsorbent surface.
4

In Langmuir’s mode of adsorption of a gas on a solid surface

  1. the adsorption at a single site on the surface may involve multiple molecules at the same time.
  2. the mass of gas striking a given area of surface is independent of the pressure of the gas.
  3. the mass of gas striking a given area of surface is proportional to the pressure of the gas.
  4. the rate of dissociation of adsorbed molecules from the surface does not depend on the surface covered.
5

The disperse phase in colloidal iron (III) hydroxide and colloidal gold is positively and negatively charged, respectively. Which of the following statements is NOT correct?

  1. Coagulation in both sols can be  brought about by electrophoresis.
  2. Sodium sulphate solution causes coagulation in both sols.
  3. Mixing of the sols has no effect.
  4. Magnesium chloride solution coagulates, the gold sol more readily than the iron (III) hydroxide sol.
6

For a linear plot of log (x/m) versus log p in a Freundlich adsorption isotherm, which of the following statements is correct ? (k and n are constants)

  1. 1/n appears as the intercept.
  2. Only 1/n appears as the slope.
  3. log (1/n) appears as the intercept.
  4. Both k and 1/n appear in the slope term.