Date of Graduation


Document Type


Degree Name

Bachelor of Science in Chemical Engineering

Degree Level



Chemical Engineering


Souto Melgar, Natacha


Diffusion is defined as the net transfer of a molecule from a high concentration region to a low concentration region. The concept of diffusion is used in a very important process called "desalination." Desalination is a separation process used to reduce the salt content dissolved in brackish water to make it suitable for human consumption, irrigation, and industrial use.

In desalination plants, it is important to monitor the constantly changing salt content of water, partly due to the diffusive effect. The main purpose of this experiment was to study the diffusion of NaCl in water at two NaCl concentrations. The diffusion was studied by measuring the change in conductivity of pure water as the brine diffuses into the water through the diffusion cell. In this experiment, the diffusion of 1M and 2M NaCl solutions was conducted and the diffusion coefficient of the NaCl determined experimentally. The experimental diffusion coefficients were compared at each NaCl and with a theoretical value. To conduct the experiment, an Armfield Diffusion Apparatus was used with a conductivity meter attached to a PC computer to take measurements of the conductivity over the course of 30 minutes. At 1M, the theoretical value was 2.2 x 10-5 cm2s-1,while the experimental results ranged from 2.20 x 10-5 cm2s-1 - 3.20 x 10-5 cm2s-1. At 2M, the theoretical value was 1.48 x 10-5 cm2s-1 and the experimental results ranged from 1.10 x 10-5 cm2s-1-2.80 x 10-5 cm2s-1. The percent error at 1M ranged from 0.25-45 % and at 2M, the percent error ranged from 3.27-89%. The cause of error for both experiments was determined to be more random than systematic since the coefficients varied significantly from each other. Recommendations for future experiments are to increase the run time, possibly change the solution mixing method, and take extra care to ensure the concentration of solution is not disrupted.


Diffusion, Fick's Law, Desalination