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प्रश्न
Explain graphically Freundlich adsorption isotherm.
उत्तर
Graphical representation of the Freundlich adsorption isotherm:
Variation of x/m with P according to Freundlich equation (Adsorption isotherm)
- Freundlich proposed the following empirical equation for the adsorption of a gas on a solid.
`"x"/"m" = "k P"^(1//"n")` (n > 1) ....(i)
where.
x = Mass of the gas adsorbed
m = Mass of the adsorbent
`"x"/"m"` = Mass of gas adsorbed per unit mass of adsorbent
P = Equilibrium pressure
k and n are constants which depend on the nature of adsorbate, adsorbent and temperature. - The graphical representation of the Freundlich equation is as shown in the adjacent plot of `x/m` vs ‘P’.
- In case of solution, P in the equation (i) is replaced by the concentration (C) and thus,
`"x"/"m" = "k C"^(1//"n")` ....(ii)
- By taking logarithm on both sides of the equation (ii), we get
`log "x"/"m" = log "k" + 1/"n" log "C"` ...(iii) - On plotting a graph of log `"x"/"m"` against log C or log P, a straight line is obtained as shown in the adjacent plot. The slope of the straight line is `1/"n"` and intercept on Y-axis is log k.
- The factor `1/"n"` ranges from 0 to 1. Equation (iii) holds good over a limited range of pressures.
a. When `1/"n"-> 0, "x"/"m" ->` constant, the adsorption is independent of pressure.
b. When `1/"n" = 1, "x"/"m" = "kP", i.e., "x"/"m" prop "P"`, the adsorption varies directly with pressure.
c. The experimental isotherms tend to saturate at high pressure.
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संबंधित प्रश्न
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