Question:

Adsorption of a gas on a metal oxide surface follows Freundlich adsorption isotherm. At $300\text{ K}$, the slope and intercept of this isotherm are 2 and 1.0 respectively. What is the value of $\frac{x}{m}$ when the pressure of the gas is 4 bar?

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Always double check if the intercept given is using base 10 logarithm or natural logarithm.
In standard textbooks, Freundlich log-plots are plotted with $\log_{10}$ by default, meaning Intercept = $1.0 \implies k = 10$.
Updated On: Jul 22, 2026
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The Correct Option is C

Solution and Explanation

Step 1: Understanding the Question:
The question is based on the Freundlich adsorption isotherm.
We are given the experimental parameters (slope and intercept) of the logarithmic isotherm plot at 300 K and need to calculate the extent of adsorption ($\frac{x}{m}$) at a specific pressure of 4 bar.

Step 2: Key Formula or Approach:
The Freundlich adsorption isotherm equation is:
\[ \frac{x}{m} = k P^{1/n} \] Taking the logarithm of both sides:
\[ \log \left( \frac{x}{m} \right) = \log k + \frac{1}{n} \log P \] Comparing this with the equation of a straight line ($y = mx + c$):
Slope = $\frac{1}{n}$
Intercept = $\log k$

Step 3: Detailed Explanation:

• From the given data:
Slope ($\frac{1}{n}$) = 2.
Intercept ($\log k$) = 1.0 $\implies k = 10^{1.0} = 10$.
Pressure ($P$) = 4 bar.

• Let us substitute these values back into the original Freundlich equation:
\[ \frac{x}{m} = k P^{1/n} \] \[ \frac{x}{m} = 10 \times 4^2 \] \[ \frac{x}{m} = 10 \times 16 = 160 \]

• Thus, the value of $\frac{x}{m}$ is 160.


Step 4: Final Answer:
The value of $\frac{x}{m}$ is 160.
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