Chapter 30, Problem 30.1QAP

Interpretation Introduction

Interpretation:

The meaning of electroosmotic flow and the reason for itsoccurrence needs to be explained.

Concept introduction:

When electric field is applied in a liquid, the ions present in the liquid moves under the influence of potential gradient. This flow of liquid is termed as electroosmotic flow. It is most obvious is those having small channels. It occurs in buffered solutions and natural water.

Answer to Problem 30.1QAP

Electroosmotic flow of liquid is caused by gradient in potential across the capillary tube on the flowing liquid that has dissolved ions. This is caused when the capillary walls get electrically charged.

Explanation of Solution

When a capillary tube is filled with fluid having dissolved ions, and electrical field is applied, the buffer ions move to respond to the electrical charges. As the solvent which is water is neutral, it remains stationary and the fluid ions move towards its electrodes with respect to the charges applied. Below is depiction of movement of electrons:

There is coulombic force induced by charges of ions in the solution wherein its net mobile charge causes electroosmotic flow. During this process of maintaining chemical equilibrium between the solid surface and solution, there is a layer of mobile ions termed as Debye layer that forms near the interface. Hence, by applying electric field to fluid the net charge in the layer gets induced and starts to move resulting in a coulomb force. This force is called electroosmotic flow.

Conclusion

Electroosmotic flow of liquid is caused due to a potential gradient across the capillary tube on the flowing liquid containing dissolved ions. This is caused when the capillary walls get electrically charged due to the application of electric field from outside.