Liquid - Liquid Diffusivity Experiment

AIM: Estimation of Diffusivity for a liquid-liquid system

OBJECTIVES: To determine the diffusivity for a liquid-liquid system at room temperature.

PRINCIPLE/ THEORY:

The diffusion coefficient is determined by using the relation
DAB = 1/ Bt ln(n1- n2)/ (n3-n4)
Where Bt is the cell constant {(2 * 104 – 3 * 104) m-2}
(n1- n2) = Initial conc. Difference
(n3- n4) = Final conc. Difference

Determination of Diffusivity Experiment Set Up

Cell constant can be determined by conducting experiments with a solution of known diffusivity.

EQUIPMENT USED: Liquid-liquid diffusion apparatus

MATERIALS USED: NaOH, H2O

EXPERIMENTAL PROCEDURE:

1. Prepare approximately 0.1N standard oxalic acid solution (N1) by weighing required amount.
2. Prepare approximately .01N solution of NaOH and HCl.
3. Standardize these solutions by titrating acid Vs NaOH (N2) and NaOH Vs HCl (N3).
4. Prepare a 1N solution of NaOH in a reagent bottle of 500 ml capacity. Pipette out 10 ml of this solution and dilute it exactly to 100 ml in a volumetric flask. Pipette out 10 ml of this diluted solution.
5. Titrate this solution against standard HCl solution and determine its concentration (N4). The cons. Of the NaOH solution in reagent bottle will be equal to N5=N4 x X dilution factor (10).
6. Clean the cell and the solvent section with the distilled water and dry the cell by keeping in a dissector for about 15-min.
7. Fill the solvent bottle with the solvent (water) and carefully locate it in the water bath.
8. Adjust the bath temperature to the required level by means of the regulator.
9. Fill the cell with 10 ml of the solution prepared in the reagent bottle. Place it in the outer bottle containing the solvent such that the liquid levels in both the inner and outer bottles are the same. That is essential to create hydraulic balance and to prevent the bulk flow of fluids. Simultaneously the magnetic stirrer is switched on with a very low speed and the stopwatch is started.
10. Carry out the experiment for a known time (20min.) stop the stirrer and immediately withdraw the solute bottle from the outer bottle. The solvent in the outer bottle is analyzed for its cons. by titrating with the std. HCl.
11. Repeat the experiment for different temperatures to find out the effect of temperature on diffusivity coefficient.

OBSERVATIONS:

Conc. Of Oxalic acid = N1 g mol / lt

Conc. Of NaOH = N2 ­­, ,

Conc. Of HCl = N3 , ,

Conc. of NaOH in 100 ml std.flask = N4 , , 

Conc. of NaOH in reagent bottle = N 5 , ,

Volume of NaOH solution taken = V1 ml

Volume of water taken = V2 , ,

Initial conc. Of NaOH in the cell = n 1 gmol/lt

Initial conc. Of NaOH in Water = n 2 gmol/lt

Final conc. Of NaOH in the cell = n 3 gmol/lt

Final conc. Of NaOH in Water = n 4 gmol/lt

DATA ANALYSIS/CALCULATIONS: 

The diffusion coefficient is determined by using the relation 

DAB = 1/ Bt ln(n1- n2)/ (n3-n4)

Where Bt is the cell constant ( to be determined)

(n1- n2) = Initial conc. difference

(n3- n4) = Final conc. difference

Cell constant can be determined by conducting experiments with solution of known diffusivity.

RESULT: 

The diffusion coefficient of NaOH in water is = m2/min.