EXPERIMENT 3

LIQUID DIFFUSION APPARATUS

1. Objective

Understanding the calibration of different mol of CaCO3 to obtain Cm value.

Demonstration of liquid diffusion.

Determine the diffusion coefficient of CaCO3 solution in deionized water.

2. Introduction

Diffusion can be described as a mixing process on a microscopic scale, caused by the

molecular motion of the particles. In liquids it is a slow process, and this slowness is

responsible for its importance. It can be the rate determining step in many mass transfer

operations, such as distillation, extraction, and in industrial reactions using porous catalyst. It

controls, for instance, the release of flavour from food. Therefore, knowledge of diffusion

rates is important for the design of process equipment. The common models can describe

molecular diffusion in multicomponent liquids is a generalisation of Fick’s Law to

multicomponent system. Fick’s law is a phenomenological description of diffusion for binary

liquid systems. Molecular diffusion describes the relative motion of individual molecules in a

mixture induced by their thermal energy causing random, irregular movements. But it may

also arise from pressure gradients, temperature gradients, external force fields, and

concentration gradients. The resulting net diffusion flux is down the potential gradient, i.e. in

the case of a concentration gradient from regions of higher to lower concentration until

uniformity of the system is reached.

3. Equipment

LEGEND

A = J- Tube stand

B = J- Tube with honeycomb

C = Conductivity probe

D = Conductivity meter

E = Magnetic stirrer

F = Liquid vessel

4. Safety and precaution

Be careful when handling the glassware

Do not attempt to change the setting of the digital conductivity meter

Wear protection glove and eyewear when preparing the test solution

5. Procedure

5.1 Pre-procedure

1. Before conducting the experiment read the safety instruction.

2. Before lab sessions read and understand the theory for liquid diffusion.

3. The accessories need to be prepared for the experiment.

5.2 Experiment Procedure

Experiment A

1. The solution for 0.001, 0.0012, 0.0014, 0.0016, 0.0018 and 0.002 M of CaCO3 was

prepared.

2. The conductivity value for all the different M of CaCO3 was determine by using the

conductivity probe and meter (C,D).

3. The reading was recorded in the table provided.

4. The graph of concentration of Ca2CO3 versus conductivity (Siemens) was computed. The

slope of this line is the (CM).

5. By using deionized water clean and washed the probe to removed all traces of salt after

finished the experiment.

Experiment B

1. The solution of 0.1 M CaCO3 was prepared.

2. The number of capillaries (holes) of the PVC round plate in the J-tube (B) was

determined. (the diameter is 2mm while the height is 6.8mm)

3. The higher end of the J-tube was clamped to the J-tube clamper (A). During clamping the

J tube need to be careful.

4. CaCO3 solution was poured into the J-tube until the liquid just reached the tops of the

capillaries. The excess solution need to wipe kindly by using soft tissue.

5. The conductivity probe (C) was inserted to the liquid vessel (F). The cable are ensured

connected to the digital conductivity meter (D).

6. The digital meter was connected to laboratory 240V AC power supply. The power supply

was switched on.

7. The liquid vessel was placed on the magnetic stirrer (E). The white magnetic bar was

placed into the liquid vessel.

8. 1000ml of deionized water was poured into the test vessel (F).

9. The magnetic stirrer was switched ON. Regulated the stirring speed to about 200 rpm.

10. The conductivity meter was switched ON. Reading shown in the meter was ensured.

11. The J-tube was placed into test vessel. During this procedure make sure that is careful. No

solution should be dropped to the deionized water.

12. The test vessel was filled with small amount of deionized water until the capillary tops

are submerged approximately 5mm below the surface of the water.

13. Start the stop watch when the capillary tops was submerged.

14. Kindly take the conductivity value for every 5 minutes elapsed until 30 minutes.

15. Removed all the glassware and rinse with deionized water after the experiment is done.

16. Disposed the test liquid in the laboratory sink.

6. Results

Experiment A

Concentration (Mol/L) Mass (g) Conductivity (µS)

0.001 0.05 204

0.0012 0.06 201

0.0014 0.07 206

0.0016 0.08 202

0.0018 0.09 205

0.002 0.10 203

CaCO3 = 100.23 g, Volume of solution: 500ml = 0.5 L

Calculation for Determining the Mass of CaCO3

To prepare 0.001 M, 0.0012 M, 0.0014 M, 0.0016 M,0.0018 M, 0.002 M solution;

100 g/ mol x 0.001 mol/L = 0.1 g/L x 0.5 L = 0.05 g

100 g/ mol x 0.0012 mol/L = 0.12 g/L x 0.5 L = 0.06 g

100 g/ mol x 0.0014mol/L = 0.14 g/L x 0.5 L = 0.07 g

100 g/ mol x 0.0016 mol/L = 0.16 g/L x 0.5 L = 0.08 g

100 g/ mol x 0.0018 mol/L = 0.18 g/L x 0.5 L = 0.09 g

100 g/ mol x 0.002 mol/L = 0.2 g/L x 0.5 L = 0.1 g

Experiment B

Concentration = 0.1 M, Volume of solution: 50 mL = 0.05 L

Calculation for Determining the Mass of CaCO3

100 g/ mol x 0.001 mol/L = 0.1 g/L x 0.05 L = 0.005 g

Time (Minute) Conductivity (µS)

0 190

5 190

10 190

15 191

20 191

25 192

30 192

Graph for experiment A :

Graph for experiment B :

For experiment B, the diffusion of CaCO3 can be determined using the following equation;

D = (4∙V∙X / M∙N∙ d2Π∙CM) x (Dk/Dt)

Where

D = diffusion

V = volume of water container for the J tube (1000mL)

X = height of J tube

M = moles of CaCO3

N = number of capillary on J tube

d = diameter of J tube

CM = slope value from experiment 1

(Dk/Dt) = slope value from experiment 2

7. Discussion

From experiment A, it can be observed that the values given off by the conductivity meter

fluctuates to inconsistent values. The value changes so well that it is as though as the

concentration is increased (0.001M, 0.0012 M so forth) they have no direct relation with the

conductivity displayed. This is due to the amount of moles of calcium carbonate in the

solution that is too low, not every particle within the solution participates actively in the

reaction with water.

Experiment B is somewhat similar to experiment A. As time lapses, the conductivity

meter increases but lands flat under certain interval. For instance, during the first 10 minutes,

the value remains at 190 µS before it rises to 191µS 5 minutes later. The experiment ends

after it is conducted for 30 minutes and the final value reads 192 µS. Difference with

experiment A is that the value gradually increases with time, instead of fluctuating

inappropriately when more concentrated mixture is introduced to the conductivity meter.

Reason why this phenomenon occurs is because the solution used is only at 0.1 M of calcium

carbonate, therefore large difference of value cannot be expected.

8. Question

8.1 Give three (3) example of liquid phase diffusion phenomenon in the environment.

Diffusion phenomenon of sugar molecules from high concentration to low one.

Diffusion phenomenon when one drop of ink is spreading in a cool and hot water.

Diffusion phenomenon when I2 molecules are spreading in alcohol.

8.2 Describe why conductivity can be use as a parameter to measure the rate of mass

transfer in this experiment.

The parameters to describe the retention properties of the liquid and the capillary

movement of the liquid were determined by using experiment. The conductivity can

use to measure the rate of mass transfer because the readings are accurate and this is

one the equipment that suitable to use in laboratory and easier to handle.

9. Conclusion

The objective of the experiment is to understand the calibration of different mol of CaCO3 to

obtain Cm value. Besides that, it is aimed to demonstrate the diffusion of liquid. It is also

conducted to determine the diffusion coefficient of CaCO3 solution in deionized water.

Based from the experiment, it is found that diffusion, a mixing process on a

microscopic scale, caused by the molecular motion of the particles, of calcium carbonate in

water can be observed and determined by it’s conductivity. This is done by conducting the

experiment based on the instructions found in this written report. On that basis as well, safety

aspects was not neglected. Glassware was handled with care, the setting of the conductivity

meter was not readjusted and necessary protective gear was worn when preparing the test

solution.

Knowledge of diffusion rates is important for the design of process equipment.

Therefore this is the reason why the experiment was conducted, so to provide students with

necessary exposure, especially with a simple experiment as such.

10. Reference

http://iopscience.iop.org/0508-3443/6/4/306/.../0508-3443_6_4_306.pdf

www.legionbrothers.com/products_heat.html

www.mechanicalduniya.com/.../practical-list-for-heat-and-mass.html