Question

Observe the given adsorption isotherm carefully and choose the correct option.
(i) These curves indicate that at a fixed temperature, there is a decrease in physical adsorption with increase in pressure.
(ii) These curves always seem to approach saturation at high pressure.
(iii) $\frac{x}{m}=k{p}^{1/n}$(n>1) is generally represented by this isotherm.
(iv) These curves indicate that at a fixed pressure, there is a decrease in physcial adsorption with increase in temperature.

• A. (i) and (iii) only
• B. (ii) and (iv) only
• C. (ii), (iii) and (iv) only
• D. All of these

Answer 1

Answer: (C)

(ii), (iii) and (iv) only

Freundlich gave an empirical relationship between the quantity of gas adsorbed by a unit mass of solid adsorbent and pressure at a particular temperature. The relationship can be expressed by the following equation:

$⟹$ $\frac{x}{m}=k\times$$(p{)}^{\frac{1}{n}}$

where $x$ is the mass of the gas adsorbed on mass m of the adsorbent at pressure $P,k$ and $n$ are constants which depend on the nature of the adsorbent and the gas at a particular temperature.

Here, the value of n should be always greater than one so as to equation be valid for a range of values.

• At higher pressure, the curves approach to a saturation level and the equation becomes invalid at higher pressures.
• If the pressure is fixed, the temperature and physical adsorption are inversely related.

Hence, here option C gives the combination of correct statements.