Question

The graph plotted between log x/m (where x is the mass of adsorbate and m is the mass of the adsorbent) vs. log P was found to be a straight line. The slope and intercept of line leads to 1/n and log K values. Find the wrong statement:

• A. The relation does not hold good at high pressures
• B. The relation fails when chemical adsorption takes place
• C. At a very low pressure, n = 1
• D. On increasing the pressure, the value of n decreases

Answer 1

The correct option is D On increasing the pressure, the value of n decreases

The correct option is (d)
This question talks about Freundlich adsorption isotherm. According to Freundlich isotherm
$\frac{x}{m}=k.P^{\frac{1}{n}}$
The plot of this equation will be:

From the graph,
a) At high pressure, adsorption becomes pressure independent. Thus, it does not hold good at high pressure.
b) Chemisorption is caused by chemical bond formation and it depends on the way how adsorbate particles react with the adsorbent. So the relation fails when chemisorption takes place.
c) In the initial part,the graph is almost a straight line.Thus it tells that the adsorption is directly proportional to pressure in this region. Hence at very low pressure n=1.
d) With an increase in pressure, the value of n increases because at high pressure adsorption becomes independent of pressure i.e. the equation at high pressure turns to be
$\frac{x}{m}=k.P^0$
This is possible only if value of n is large in high pressure.So the statement of option (d) is not correct.