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BACKGROUND
In 1909, Freundlich gave an empirical expression representing the isothermal variation of adsorbtion of a quantity of gas adsorbed by unit mass of solid adsorbent with pressure. This equation is known as Freundlich adsorption isotherm or Freundlich Adsorption equation.
Plotting a graph between log(x/m) and log p, we will get a straight line with value of slope equal to 1/n and log k as y-axis intercept.1,2
Aim of the expt
To verify Freundlich adsobtion isotherm and to determine the constants ‘k’ and ‘b’ invovlved in the isotherm equation.
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REQUIREMENTS
Apparatus : Reagent bottles,
Beakers,
Burette,
Pipette,
Stand,
Conical flask,
Const.
Temperature bath etc.
Chemicals : Distilled water,
Activated charcoal,
0.5 N acetic acid,
0.1N NaOH
Phenolphthalein indicator.
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PROCEDURE
Prepare 0.5N acetic acid solution and detemine its exact normality (NA) by titrating against 0.1N NaOH using phenolphthalein indicator (end point pink colour). Prepare following mixtures of acetic acid and distilled water in 5 separate reagent bottles and label them as A,B,C,D, and E.Add 1 gm of activated charcoal to each of the five reagent bottles and keep them in constant temperature water bath for 1 hr to attain adsorption equilibrium.Shake the bottle occasionally during the hour.Using dry glass-ware,filter all the mixtures separately.Titarte 10ml of filterate from each bottle against 0.1N NaOH using phenolphthalein as the indicator and determine corespnding effective normalitiesof each of the solution (N2).(End point pink colour.
Observation
- Water bath temp. = ……..oC
- Mass of activated charcoal (m) = ……..gm
-
Exact normality of acetic acid solution (NA) =……..
- Where, N1 = initial normality (before adsorption)
- = initial conc. Of acetic acid in gm equivalent/litre
- C = N2 = Equilibrium normality (at adsorption equilibrium)
- = equilibrium conc. Of acetic acid in gm equivalent/litre
- N1 – N2 = gram equivalent of acetic acid adsorbed per litre of solution
Calculation
- Calcuation of exact normality of acetic acid solution.
- Calculation of acetic acid adsorbed.
- Calculation of k and b
- Plot the graph of log (w/m) vs log C
-
Freundlich adsorption isotherm equation
| Log (w/m) = (1/b)log C + log K |
Observation table:
| Bottle | Distilled water (ml) |
Acetic acid (ml) |
Effective normality of acetic acid solution(N1) |
| A | 0 0 | 50 | 1×NA = |
| B | 10 | 40 | 0.8×NA = |
| C | 20 | 30 | 0.6×NA= |
| D | 30 | 20 | 0.4×NA = |
| E | 40 | 10 | 0.2×NA = |
| Bottle | N1 | C=N2 | Log C | W=3(N1-N2) | w/m =w | C/w/m |
| A | ||||||
| B | ||||||
| C | ||||||
| D | ||||||
| E |
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CONCLUSION
The values of constant of ‘k’ and ‘b’ of the Freundlich adsorption – isotherm equation are……… and………respectively.
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