Among the following the number of curves not in accordance with Freundlich adsorption isotherm is ________.
(a)
(b)
(c)
(d)

Solution

Chemistry ma’am · 3 steps

Take logs of Freundlich's equation first, then check each graph's axes before you look at its shape.

1. Linear form. Freundlich's isotherm is x/m = kP^(1/n) with n > 1. Taking logs turns it into a straight-line equation.

   log x/m = log k + 1/n log P

2. What it predicts. Plot log x/m against log P. You get a straight line with positive slope 1/n and intercept log k on the log x/m axis. A graph fits only if it shows exactly this, with these axes.

   Graph	Axes	Shape	Fits Freundlich?
   (a)	log x/m vs log P	curve	No, the log form must be straight
   (b)	log x/m vs P	line through origin	No, x-axis is P, not log P
   (c)	log x/m vs P	line with intercept	No, x-axis is P, not log P
   (d)	log x/m vs log P	line with intercept log k	Yes

3. So. Only (d) follows the Freundlich isotherm. Graphs (a), (b) and (c) do not, so the answer is 3.

The common slip: 2. Matching graph (c) to the straight-line shape without noticing its x-axis is P, not log P, gives 2.

The idea to keep. For any isotherm question, write the log form first. Freundlich gives a straight line of slope 1/n and intercept log k, but only on a log x/m versus log P plot.

Answer from the NTA final answer key. Solution by PrepWiser.