CEBU INSTITUTE OF TECHNOLOGYU N I V E R S I T Y

Physical Chemistry IILaboratory

ADSORPTION FROM SOLUTIONS: ACETIC ACID ON CHARCOAL

TITLE OF EXPERIMENT

JOELREY M. TAGAMABSChE

ENGR. ROSARIO DANGININSTRUCTOR

I. ABSTRACT

The adsorption of acetic acid in activated carbon is measured and the results were compared to the Freundlich adsorption isotherm,

xm

= kCn

Where 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 solution and 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 the activated carbon drained with the acetic acid solution.

II. OBJECTIVE

To determine the values of k and n of the Freundlich adsorption isotherm.

III. APPARATUS AND MATERIALS

25 mL Burette100 mL calibrated flask2 small long stemmed funnels9 cm filter paper20 g of active charcoal250 mL of 0.50 M CH3COOH150 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 phenolphthalein as 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, the temperature were kept constant at 25 OC. The mixtures were filtered through the 9cm filter paper. From the most concentrated mixture, sample were taken accordingly, 5 mL, 10 mL, 25 mL, 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 ReversibilityThe charcoal left at the filter paper was transferred to a 100 mL volumetric

flask using a wash bottle to ensure that nothing adheres to the filter paper. Volume was set to 100 mL.Shaken frequently at an interval for 30 minutes. The solution was filtered and titrated with standard NaOH solution.

V. SKETCH

VI. TABULATED DATA AND RESULTS

Table1. Raw Data taken after Titration

HAc, Acetic Acid Solution, M

V, volume of 0.100 M NaOH, ml

0.50 26.00.250 23.00.125 24.7

0.0625 26.90.0313 23.00.0156 7.70

Left: The Mixture of Acetic acid solution and activated charcoal.

Bottom Left: Improvised water bath to keep solutions at 25oC.

Bottom Right: Filtration Setup

Below: End Point, Reverse

Table 2.Calculation Summary

Co V C X= Co-CX/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 -0.94500.125 26.9 0.2690 0.0981 0.0491 -1.0083 -1.3089

0.0625 23.0 0.0230 0.0395 0.0198 -1.4034 -1.70330.0313 7.70 0.0077 0.0243 0.0122 -1.6144 -1.91360.0156 2.30 0.0023 0.0133 0.0067 -1.8761 -2.1739

Figure 1. Graph of log (X/m)vs. log C

VII. CALCULATIONS

Let Co = initial concentration of the acetic acid solution

C = final concentration of the acetic acid solution after adsorptionX = concentration of the adsorbed acid

= Co – Cm = weight of the carbon used

= 2 gramsV = volume of the base

-2.4 -2.2 -2 -1.8 -1.6 -1.4 -1.2 -1 -0.8 -0.6 -0.4

-2

-1.8

-1.6

-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

1; -0.3242

2; -0.674

3; -1.0083

4; -1.4034

5; -1.6144

6; -1.8761

R² = 0.999643576156136

log x/m vs. log C

log x/m

log C

y = 0.9935x + 0.2855

Determine the concentration of the acetic acid solution after adsorption from the volume of the base titrated.

C = V (concentrationof the base)Volumeof the solution

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 the Freundlich equation:

xm

= kCn

the validity of the isotherm can be tested by taking its natural logarithm. The equation then becomes

log10 X/m = log10 k + n log10 C

If log10 X/m is plotted against log10 C, a straight line results with the slope equal to n and the intercept equal to log10 k.

From figure 1, we have identified that the graph follows a straight line after regression with R2 = 0.9996. Therefore, from the plot, values of k and n can now determined to be

n = 0.9935k = 0.2855

VIII. CONCLUSION

The adsorption of the acetic acid in charcoal follows the Freundlich adsorption isotherm. It is also evident that adsorption decreases as the concentration of the solution decreases. Thus, k value remains constant at a given temperature.

IX. REFERENCES

Atkins, Peter and de Paula, Julio. Atkins Physical Chemistry, 7th edition. W.H. Freeman and Company, 2006

http://gmuphyschemlab.pbworks.com/f/expt6-1.pdf

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