Freundlich Isotherm MCQ - Practice Questions & Answers

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EASY

According to Freundlich adsorption isotherm, which of the following is correct ?

$\frac{x}{m}\propto P^o$

$\frac{x}{m}\propto P^1$

$\frac{x}{m}\propto P^{1/n}$

All the above are correct for different ranges of pressure

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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)

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

1/n appears as the intercept.

Only 1/n appears as the slope.

log (1/n) appears as the intercept.

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Concepts Covered - 0

Freundlich Isotherm

Freundlich adsorption isotherm:

Freundlich, in 1909, gave an empirical relationship between the quantity of gas adsorbed by unit mass of solid adsorbent and pressure at a particular temperature. The relationship can be expressed by the following equation:

$\frac{x}{m}= K.p^{1/n}$ (n>1)

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.

The relationship is generally represented in the form of a curve where mass of the gas adsorbed per gram of the adsorbent is plotted against pressure (Fig). These curves indicate that at a fixed pressure, there is a decrease in physical adsorption with increase in temperature. These curves always seem to approach saturation at high pressure.

Surface Chemistry Image 1

Logarithmic graph of Freundlich isotherm

Taking logarithm of eq. we get

$log\frac{x}{m}= log K+\frac{1}{n}log p$

The validity of Freundlich isotherm can be verified by plotting log x m on y-axis (ordinate) and log p on x-axis (abscissa). If it comes to be a straight line, the Freundlich isotherm is valid, otherwise not (Fig.). The slope of the straight line gives the value of $\frac{1}{n}$ . The intercept on the y-axis gives the value of log k.