Surface Chemistry : Level 3

Which one of the following is an example of adsorption?

• ammonia in contact with water

• ammonia in contact with hydrogen gas

• silica gel in contact with water vapors

• None of above

In Freundlich Adsorption isotherm, the value of 1/n is

• 1 in case of physical adsorption

• 1 in case of chemical adsorption

• Between 0 and 1 in all cases

• Less than 0 all cases

Which of the following statements is incorrect regarding physisorption?

• It occurs because of van der Walls forces

• More easily liquefiable gases are adsorbed readily

• Under high pressure it results into multimolecular layer on adsorbent surface

• Enthalpy of adsorption (ΔH_adsorption) is low and positive

Rate of physical adsorption increase with

• Increase in temperature

• Decrease in pressure

• Decrease in temperature

• Decrease in surface area

The Langmuir adsorption isotherm is deduced using the assumption

• The adsorbed molecules interact with each other

• The adsorption takes place in multilayers

• The adsorption sites are equivalent in their ability to adsorb the particles

• The heat of adsorption varies with coverage

A plot of log x/m versus log p for the adsorption of a gas on a solid gives a straight line with slope equal to

• n

• 1/n

• log k

• -log k

In Langmuir's model of adsorption of a gas on a solid surface

• the adsorption at a single site on the surface may involve multiple molecules at the same time

• the mass of gas striking a given area of surface is proportional to the pressure of the gas

• the mass of gas striking a given area of surface is independent of the pressure of the gas

• the rate of dissociation of adsorbed molecules from the surface does not depend on the surface covered

Which one of the following characteristics is associated with adsorption?

• ΔG and ΔH are negative but ΔS is positive

• ΔG and ΔS are negative but ΔH is positive

• ΔG is negative but ΔH and ΔS are positive

• ΔG, ΔH and ΔS all are negative

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/n appears as the intercept

• Only 1/n appears as the slope

• log(1/n) appears as the intercept

• Both k and 1/n appear in the slope term

Activated charcoal is used to remove coloring matter from pure substances. It works by___________.

• Sorption

• Absorption

• Adsorption

• Bleaching