Difference Between Absorption and Adsorption

The key difference between absorption and adsorption is that in absorption, one substance (matter or energy) takes another substance into that substance whereas in adsorption only the surface level interactions are taking place.

Sorption is the process where one substance takes up or holds another substance. This can be a chemical phenomenon since chemical bonds involved in taking up and holding two substances. Sorption is advantageous in some occasions, but sometimes it is disadvantageous too. For example, sorption can reduce ground-level water contamination. When we add contaminants to the soil, they are attracted to soil; thus, their movement to underground soil layers slows down. Eventually, this will result in low contamination. As sorption reactions occur quickly, it takes less time. Sorption can be of two types, absorption and adsorption.

CONTENTS

1. Overview and Key Difference
2. What is Absorption
3. What is Adsorption
4. Side by Side Comparison – Absorption vs Adsorption in Tabular Form
5. Summary

What is Absorption?

In absorption, one substance is taken up into the physical structure of the other substance. The substance, which is absorbing into another substance, is the “absorbate.” The substance that absorbs the absorbate is the “absorbent.”

For example, if an organic molecule goes inside a solid particle (soil particle), then the organic molecule is the absorbate, and the soil particle is the absorbent. The absorbent can be a gas, liquid or a solid, whereas the absorbate can be an atom, ion or a molecule. Normally, absorbate and the absorbent are in two different phases.

Absorption property of chemicals is used in various occasions. For example, this is the principle behind liquid-liquid extraction. Here, we can extract a solute from one liquid to another liquid, because the solute is more absorbed in one liquid than the other when they are in the same container. In order to absorb, the absorbent should have a porous structure or enough space in which the absorbate can accommodate. Moreover, the absorbate molecule should have a suitable size, to go inside the absorbent structure. Further, the attractive forces between two components facilitate the absorption process. Same as a mass; energy also can undergo absorption (into substances). This is the foundation behind spectrophotometry. There, atoms, molecules or another species absorb light.

What is Adsorption?

In adsorption, a substance or energy is attracted to a surface of another matter. The attracted substance is “adsorbate”, and the surface is “adsorbent.” The attraction between organic materials and activated charcoal is an example of adsorption. Organic material is the adsorbate in this occasion, and the adsorbent is activated charcoal.

Another example of adsorption is attracting protein onto biomaterial. Adsorption occurs in three types, physical adsorption, chemisorption, and electrostatic adsorption. In physical adsorption, weak van der Waals forces are the attracting forces. In chemisorption, the attraction is taking place via a chemical reaction between the adsorbent and the adsorbate. As the name suggests, in electrostatic adsorption, electrostatic interactions are forming between ions and the surfaces.

What is the Difference Between Absorption and Adsorption?

Summary – Absorption vs Adsorption

Absorption and adsorption are two forms of sorption processes. The difference between absorption and adsorption is that, in absorption, one substance (matter or energy) takes another substance into that substance whereas in adsorption only the surface level interactions are taking place.

Reference:

1. “Sorption.” Wikipedia, Wikimedia Foundation, 28 Feb. 2018. Available here  
2. Helmenstine, Anne Marie, Ph.D. “Absorption – Chemistry Glossary Definition.” ThoughtCo, Jun. 24, 2014. Available here 

Image Courtesy:

1.’Absorption vs adsorption’By Daniele Pugliesi (CC BY-SA 3.0) via Commons Wikimedia