CEBU INSTITUTE OF TECHNOLOGY U N I V E R S I T Y Physical Chemistry II Laboratory ADSORPTION FROM SOLUTIONS: ACETIC ACID ON CHARCOAL TITLE OF EXPERIMENT JOELREY M. TAGAMA BSChE ENGR. ROSARIO DANGIN INSTRUCTOR
I. ABSTRACT The adsorption of acetic acid in activated carbon is measured and the results werecompared to the Freundlich adsorption isotherm, = kCnWhere m is the weight of the charcoal and k and n are constants. The method used is carried out through a beaker where mixing of the aceticacid solutionand activated carbon occurs. At equilibrium, the concentration of the acetic acid is determined.The weight, x of solute adsorbed is equal to the change in molar concentration of the solution,Co-C, solute and the volume of the solution. x = (Co-C) MV To demonstrate that the type of adsorption is reversible, water is introduce to theactivated carbon drained with the acetic acid solution.
II. OBJECTIVE To determine the values of k and nof the Freundlich adsorption isotherm. III. APPARATUS AND MATERIALS 25 mL Burette 100 mL calibrated flask 2 small long stemmed funnels 9 cm filter paper 20 g of active charcoal 250 mL of 0.50 M CH3COOH 150 mL of standard 0.10 M NaOH IV. PROCEDURE A. Standardization of CH3COOH Five (5) mL samples of CH3COOH were titrated with 0.100 M NaOH using phenolphthaleinas indicator. After an hour, the equilibrium concentrations were determined. B. Preparation of the test samples Two (2) grams of charcoal were weighed and placed each of the six (6) 250 mL flask.CH3COOH solution is placed to each flask with the concentrations as follows: 0.50 M, 0.25 M ,0.125 M, 0.0625 M, 0.0313 M, 0.0156 M. Shaken at frequent intervals with cover for an hour, thetemperature were kept constant at 25 OC. The mixtures were filtered through the 9cm filterpaper. From the most concentrated mixture, sample were taken accordingly, 5 mL, 10 mL, 25mL, and 50 mL of the remaining two. C. Titration of the test sample Samples were titrated with the 0.100 M NaOH using phenolphthalein as indicator.Duplicate titrations were made. D. Demonstration of Reversibility
The charcoal left at the filter paper was transferred to a 100 mL volumetric flask using awash bottle to ensure that nothing adheres to the filter paper. Volume was set to 100mL.Shaken frequently at an interval for 30 minutes. The solution was filtered and titratedwith standard NaOH solution.V. SKETCH Left: The Mixture of Acetic acid solution and activated charcoal. Bottom Left: Improvised water bath to keep o solutions at 25 C. Bottom Right: Filtration Setup Below: End Point, Reverse
VI. TABULATED DATA AND RESULTSTable1. Raw Data taken after Titration HAc, Acetic Acid Solution, M V, volume of 0.100 M NaOH, ml 0.50 26.0 0.250 23.0 0.125 24.7 0.0625 26.9 0.0313 23.0 0.0156 7.70Table 2.Calculation Summary Co V C X= Co-C X/m log C log (X/m) 0.50 26.0 0.0260 0.4740 0.2370 -0.3242 -0.6253 0.250 23.0 0.0230 0.2270 0.1135 -0.6740 -0.9450 0.125 26.9 0.2690 0.0981 0.0491 -1.0083 -1.3089 0.0625 23.0 0.0230 0.0395 0.0198 -1.4034 -1.7033 0.0313 7.70 0.0077 0.0243 0.0122 -1.6144 -1.9136 0.0156 2.30 0.0023 0.0133 0.0067 -1.8761 -2.1739Figure 1. Graph of log (X/m)vs. log C log x/m vs. log C 0 -2.5 -2 -1.5 -1 -0.5 0 -0.2 -0.6253, -0.3242 -0.4 R² = 0.9996 -0.6 y = 0.9935x + 0.2855 -0.945, -0.674 -0.8 -1.3089, -1.0083 -1 log C -1.2 -1.7033, -1.4034 -1.4 -1.9136, -1.6144 -1.6 -1.8 -2.1739, -1.8761 -2 log x/m log x/m vs. log C 0
VII. CALCULATIONS Let Co = initial concentration of the acetic acid solution C = final concentration of the acetic acid solution after adsorption X = concentration of the adsorbed acid = Co – C m = weight of the carbon used = 2 grams V = volume of the base Determine the concentration of the acetic acid solution after adsorption from the volumeof the base titrated. C=Where volume of the solution = 100 mL, concentration of the base = 0.100 M Calculate X from the difference of the initial and final concentrations, Co – C. From theFreundlich equation: = kCnthe validity of the isotherm can be tested by taking its natural logarithm. The equation thenbecomes log10 X/m = log10 k + n log10 CIf log10 X/m is plotted against log10 C, a straight line results with the slope equal to n andthe intercept equal to log10 k. From figure 1, we have identified that the graph follows a straight line afterregression with R2 = 0.9996. Therefore, from the plot, values of k and n can nowdetermined to be n = 0.9935 k = 0.2855
VIII. CONCLUSION The adsorption of the acetic acid in charcoal follows the Freundlich adsorptionisotherm. It is also evident that adsorption decreases as the concentration of the solutiondecreases. Thus, k value remains constant at a given temperature. IX. REFERENCESAtkins, Peter and de Paula, Julio. Atkins Physical Chemistry, 7th edition. W.H. Freeman andCompany, 2006http://gmuphyschemlab.pbworks.com/f/expt6-1.pdfViewed on September 1, 2012http://www.fpharm.uniba.sk/fileadmin/user_upload/english/Physical_Chemistry/5-Adsorption.pdfviewed on Septemer 1, 2012