Experiment 5 Surface Chemistry Adsorption OF Acetic ACID ON Activated Carbon PDF

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EXPERIMENT 8 SURFACE CHEMISTRY:ADSORPTION OF ACETIC ACIDON ACTIVATED CARBONObjectiveTo study the adsorption isotherm of acetic acid by activated carbonIntroductionSurface chemistry is the branch of chemistry that deals with process of adsorption thatoccurs on the surface of a liquid or solid. Adsorp...

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EXPERIMENT

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SURFACE CHEMISTRY: ADSORPTION OF ACETIC ACID ON ACTIVATED CARBON

Objective To study the adsorption isotherm of acetic acid by activated carbon Introduction Surface chemistry is the branch of chemistry that deals with process of adsorption that occurs on the surface of a liquid or solid. Adsorption is found in most natural physical, biological, and chemical systems and it is very important particularly for industrial purposes. The most common process involving adsorption process in industry is waste water treatment. The term adsorption is used to describe the process that occurs when a gas or liquid or solute called adsorbate accumulates on the surface of adsorbent forming a molecular or atomic film. The adsorbent can be a solid or more rarely a liquid. The adsorbate may be held on the surface either by physical attraction forces or chemical forces. The adsorption due to physical adsorption is called physisorption while the adsorption due to chemical affinity is called chemisorption. Adsorption is usually described through isotherms, that is, functions which relate the amount of adsorbate on the adsorbent with pressure of gas or concentration of liquid. There are several models of isotherms available in literature that can be used to discuss the process of adsorption such as Langmuir isotherm, Freundlich isotherm, BET isotherm and so on. Each isotherm differs from each other by the assumptions that must be made while working with these models of isotherms. In general, the amount of adsorption, Y is expressed as number of moles of adsorbate per mass of adsorbent. The amount of adsorption increases with the concentration or pressure of the adsorbate. The increase is rapid at first but as the surface of adsorbent fills with adsorbate, the rate of adsorption, dY/dc decreases. As the surface of the adsorbent becomes full, further increases in concentration would not contribute in increase of the amount adsorbed. The amount adsorbed when the surface is covered with a monolayer of the adsorbate is called Ymax. At a given concentration, the amount adsorbed decreases with increasing temperature. The Freundlich adsorption isotherm can be represented as Y = kc1/n

(1)

where Y = the amount of adsorption in of moles of adsorbate per mass of adsorbent c = concentration in mol dm3 k and n are experimentally determined constants 43

A linear form of Equation (1) is

log Y  log k  1 n log c

(2)

To test the validity of the Freundlich isotherm, a plot of log Y against log c should give a straight line with slope equal to 1/n and the y-intercept equal to log k. The equation for the Langmuir isotherm is

c c 1   Y kYmax Ymax If the system follows the Langmuir isotherm, then the plot of c/Y against c is a straight line with a slope equal to 1/Ymax and the y-intercept equal to 1/kYmax. Apparatus 1. 2. 3. 4. 5. 6. 7. 8.

250 cm3 conical flask 20 cm3 beaker burette 25 cm3 pipette 100 cm3 measuring cylinder Filter funnel Retort stand Parafilm

1. 2. 3. 4.

Activated charcoal (carbon) 0.4 M acetic acid, CH3COOH 0.1 M sodium hydroxide, NaOH Phenolphthalein indicator

Chemicals

Procedure 1. Weigh about 1.5 g of activated charcoal into each of the dry glass-stoppered flasks. 2. Prepare a series of acetic acid of various concentrations according to the Table 8.1. Use a 100 cm 3 measuring cylinder to measure the required amount of 0.4 M acetic acid and then dilute with distilled water to exactly the 100 cm3 mark. 3. Pour the prepared acetic acid solution (100 cm3) into each of the glass-stoppered conical flask containing charcoal. Swirl the flask vigorously and let them stand for a week. 4. Filter the solutions.

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Table 8.1 : Suggested volumes of 0.4 M acetic acid to be diluted to 100 cm3 Sample Volume 0.4 M acetic acid (cm3) 1 100 75 2 50 3 25 4 5 10 5 6 5. Titrate a suitable volume (refer to Table 8.2) of the filtrate with the standard 0.1M NaOH using phenolphthalein as indicator. Use a pipette to measure accurately the required aliquot. Table 8.2 : Volume of filtrate required for analysis of sample Sample Volume of filtrate (cm3) 1 10 10 2 10 3 4 25 25 5 6 40 6. Repeat the titration three times for each sample.

Results and Discussion 1.

Tabulate your results and for each sample, calculate a) the molarity of the diluted acetic acid. b) the molarity of the acetic acid in equilibrium with the adsorbent c) Y, the number of moles of acetic acid adsorbed per gram of adsorbent.

2.

Prepare suitable tables containing the quantities needed to test the validity of the Freundlich and Langmuir isotherms. Plot the isotherms and calculate the Freundlich and Langmuir parameters (where available). Discuss the observed results.

Questions 1.

The data below relate to the adsorption of N2 on rutile (TiO2) at 75 K. Confirm that they fit a BET isotherm in the range of pressure reported, and determine Vmon and c. p/Torr V/mm3

1.20 2.35

14.0 559

45.8 649

87.5 719

127.7 790

164.4 860

204.7 950

At 75 K, p* = 570 Torr. The volumes have been corrected to 1.00 atm and 273 K and refer to 1.00 g substrate.

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Experiment 8: Adsorption of acetic acid on activated carbon 1.

Pre laboratory preparation: All the pre laboratory calculations and experimental flowcharts must be clearly presented in this sheet.

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2.

Data sheet for Experiment 8 Sample Mass of activated carbon (g) Titration: Volume of NaOH (cm3) Trial 1 Trial 2 Trial 3 Average volume of NaOH (cm3)

1

2

3

4

5

4

5

Calculation: Sample Initial concentration of diluted acetic acid (mol dm3) (c) Final concentration of diluted acetic acid (mol dm3) Concentration of acetic acid (adsorbed) in equilibrium with the adsorbent (mol dm3) Amount in mole of adsorbed acetic acid per g charcoal (y)

1

2

3

Log c Log y c/y

Lecturer’s / Instructor’s signature: Date: 47

References: 1.

Beran J.A. (2009), Laboratory Manual for Principles of General Chemistry. 8 th edition, John Wiley & Sons, NJ.

2.

Emil J. Slowinski ,Wayne C Wolsey, William L Masterton, Judith W Peisen (1997), Chemical Principles in the Laboratory with Qualitative Analysis, Saunders College Publishing.

3.

Morris Hein, Leo R Best, Robert L. Miner (2006), Foundations of Chemistry in the Laboratory. 12th Edition, John Wiley.

4.

Nelson J. H., Kemp K. C. (2005), Chemistry the Central Science Laboratory Experiments, 10th Edition, Prentice Hall.

5.

Nowell J.W. Baird H.W., Crockford H.D., Getzen F. W. (1976), Laboratory Manual of Physical Chemistry.

6.

Rendle P.M, Vokins D., Davis P. (1967), Experimental Chemistry – A Laboratory Manual.

7.

Shoemaker D. P (1989) Experiments in Physical Chemistry, International Edition, McGraw-Hill.

8.

Sime Rodney J. (1990), Physical Chemistry – Methods, Techniques and Experiments, Saunders Golden Sunburst Series, Saunders College Publishing.

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