Adsorption
Chapter Name : Surface Chemistry |
Sub Topic Code : 102_12_05_02_05 |
Topic Name : Adsorption |
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Sub Topic Name : Adsorption Isotherms |
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Introduction
• The adsorption process is usually studied through graphs known as adsorption isotherms. They depict the amount of adsorbate on the adsorbent as a function of its pressure at constant temperature. • In 1909, Freundlich expressed an empirical equation (called as the Freundlich Isotherm) for representing the variation in adsorption of quantity of gas adsorbed by unit mass of solid adsorbent with pressure. • The isotherm correctly established the relationship of adsorption with pressure at lower values but it failed to predict the value of adsorption at higher pressure.
Pre-Requisites:
• Introduction of adsorption • Adsorption mechanism • Types of adsorption
Activity:
When some activated carbon is added to benzene at a particular temperature say 25 *C, its concentration decreases due to adsorption of benzene on the carbon. Also the adsorption obeys the Freundlich isotherm relation.
Real Life Question:
When does the process of adsorption, once started stops?
Key Words / FlashCards
| Key Words | Definitions (pref. in our own words) |
|---|---|
| Adsorption | It is the phenomenon of accumulation of molecules of a liquid/gas on the surface of a solid. |
| Adsorbate | It is the substance which concentrates or accumulates at the surface of another substance. |
| Adsorbent | It is the substance on which adsorption occurs i.e. on which another substance gets accumulated. |
| Physisorption | When the forces of attraction existing between the adsorbate and the adsorbent are Vander Waal’s forces, the adsorption is called physical adsorption. |
| Chemisorption | When the forces of attraction existing between the adsorbate particles and the adsorbent are almost of the same strength as chemical bonds, the adsorption is called chemical adsorption. |
| Adsorption isotherm | It is the graph between the amounts of adsorbate (x) adsorbed on the surface of adsorbent (m) and pressure at constant temperature. |
| Freundlich Adsorption Isotherm | It is an empirical relationship between the quantity of gas adsorbed by unit mass of solid adsorbent and pressure at a particular temperature. |
Learning aids / Gadgets
| Gadgets | How it can be used |
|---|---|
| Benzene | Take some concentrated benzene. |
| Activated carbon | Add some activated carbon to benzene. |
Real life uses :
Treatment of waste water, controlling humidity.
Places to visit :
Laboratory.
Practical examples around us
| Examples | Explainations |
|---|---|
| Water treatment plant | Cleaning of wastewater is done using activated carbon (char-like material). Pollutants in the water get physically adsorbed on the surface of carbon leading to cleansing of water. Also isotherms are used to find out when the filters need to be changed. |
What you learn in Theory:
The relation that defines the process of adsorption.
What you learn in Practice:
How the graphs are used to find the optimum temperature and pressure conditions at which maximum adsorption takes place.