# Surface Chemistry   Share

## What is Surface Chemistry

Surface chemistry is the branch of chemistry which deals with the study of the type of surface and the species present on it. This anomaly is studied with the help of adsorption and colloidal state which are very useful to understand the chemical and physical characteristics of the substance. The properties of substances are different at the surfaces and in the bulk because the molecules that are present in the bulk are attracted symmetrically in all direction having zero net force but the molecules present at surface familiarize attraction unequally. In this unit, we will study a phenomenon related to the surface.

Since surface chemistry deals with the interaction of surfaces of one system with that of the other system. Some anomaly work on this principle such as:

• Catalysis

• Colloid formation

• Chromatography

• Electrode reaction

Surface Chemistry plays an important role in various chemical processes such as:

• In chemical industries, the principle of catalysis is used for the preparation of chemicals.

• Drug selection by doctors like syrup or tablets is based on the reactivity of medicine which depends on surface properties.

• In electrical industries, the use in the surface and interface of microchips used in computers.

• Protein adsorption on the walls of the intestine.

• Adsorption surface phenomena are used for vacuum formation.

## Notes for Surface Chemistry

In this part, the candidate will study the:

•  Important topics of the chapter

•  Overview

•  Related formulae

• Some important tips for the preparation of the chapter at best.

2. Catalysis

3. Colloids

4. Emulsions

## Overview of the Chapter Surface Chemistry

It has been known that the surface of a liquid is in a state of unsaturation due to the unbalanced or residual forces which act along the surface of a liquid. Similar to it, the surface of a solid may also have residual forces. Thus, the surface of a solid has a tendency to attract and to retain molecules of gas or liquids with which such surfaces come in contact. This phenomenon of surfaces is termed as adsorption. Differences between Adsorption and Absorption is that Adsorption is a surface phenomenon whereas absorption is a bulk phenomenon in which the substance is symmetrically distributed throughout the body of a solid or liquid to form a solution or a compound.

In the case of adsorption, the equilibrium is easily attained in a very short interval of time whereas in absorption the equilibrium takes place slowly.

According to Freundlich adsorption isotherm:

Taking the logarithm of the above equation we get :$log\frac{x}{m}= \, logk\, +\, \frac{1}{n}logP$

Examples of adsorption and absorption

(i) Water vapour is absorbed by anhydrous calcium chloride while it is adsorbed by silica gel.

(ii) Ammonia is adsorbed by charcoal while it is absorbed by water to form ammonium hydroxide.

NH3+ H2O $\rightarrow$  NH4OH

(iii) Decolourisation of sugar solution by activated charcoal is another example of adsorption. In this example, charcoal adsorbs the colouring material and thus decolourises the solution.

Following them, one will get to know about different types of adsorption, physical adsorption and chemical adsorption.

 S.No Physisorption Chemisorption 1. It is due to the van der Waal force of attraction. The adsorption takes place because of chemical bonds. 2. It is not specific in nature. It is specific in nature. 3. It is reversible. It is irreversible. 4. Enthalpy is low. Enthalpy is high. 5. Activation energy is not needed. High activation energy is needed. 6. Multimolecular layers on adsorbent are formed. Only unimolecular layers are formed.

After studying about adsorption the candidate will learn about catalyst. Catalyst is a substance which can change the speed of chemical reaction without undergoing any change in itself whether be it mass or chemical composition at the end of the reaction. This phenomenon is known as catalysis. Catalyst can be broadly divided into two categories:

1. Homogeneous catalysis: Here reactants and catalyst are in the same phase (liquid or gas)

2. Heterogeneous catalysis: Here reactants and catalyst are in a different phase.

Talking about the important features of solid catalysts the aspirant will learn about activity and selectivity. By activity of the catalyst, we mean its capacity to increase the speed of chemical reaction. Dependence of activity is on the strength of chemisorption. By selectivity of a catalyst we mean its ability to form particular products excluding others.Moving further in this chapter the candidate will learn about the classification of colloids on the basis of:

1. Size of particles of solute

2. The physical state of the dispersed phase and the dispersion medium

3. Nature of interaction between the dispersed phase and the dispersion medium

4. Types of particles of the dispersed phase

In this part of surface chemistry, the candidate will know about micelle formation, cleansing action of soaps, different methods of preparation of colloids, methods of purification of colloidal solutions and their respective properties which include

• Electrophoresis: Electrophoresis is done to confirm the charge on colloid particles. On applying the electric potential across the electrodes, colloid particles move towards one of the electrodes as shown in the figure given below:

• Coagulation or Precipitation(learning about Hardy-Schulze rule): Coagulation is the process when the charge is removed from the colloid particles and these particles come closer to each other and precipitate or coagulate.

• Brownian movement: This is the movement of colloidal particles which is observed under a powerful microscope. In this motion, colloidal particles move in zig-zag motion in solution.

• Charge on colloidal particles: Colloidal particles carry an electric charge. This charge can be negative or positive but it is always the same for all the particles.

Lastly, one will learn about Emulsions. The emulsion is a colloidal system consisting of immiscible liquids. e.g. milk is an emulsion in which particles of liquid fat are dispersed in water. In common, however, one of the liquids is water and the other, and oily substance insoluble in it. An emulsion is a heterogeneous system consisting of more than one immiscible liquids dispersed in one another in the form of droplets. Such systems possess extremely small stability which is made by the addition of surface-active agents, finely divided solids, etc.

## Formulae chart for Surface chemistry:

1. Freundlich adsorption isotherm:

2. Langmuir adsorption isotherm:       $\Theta =\, \frac{{K}'P}{1+KP} \, or\, \frac{x}{m}= \, \frac{aP}{1+bP} where\, a ,b\, are \, constant.$

3.  $\frac{x}{m}= \, KC^{\frac{1}{n}};\, C= concentration\, of\, solute\, in\, solution$

4. Zeta potential, $Z= \frac{4\pi \eta \mu }{D}$

## How to Prepare for Surface Chemistry?

There are some chapters in chemistry which are very hard to gear up with. One of the chapters is surface chemistry. Previously not many questions were asked from this chapter but in recent years since 2012 onwards, direct questions are asked from surface chemistry.

Colloids seem to be the most favorite topic of JEE. So, the aspirant should be thorough with each and every aspect related to colloids like:

1. Identifying different types of colloids

2. Methods of preparation of colloids

3. Electrophoresis

## Some important tips to prepare surface chemistry:

1. The candidate must spend ample amount of time in understanding and learning the concepts that too from NCERT.

2. An aspirant must practice theoretical problems from this chapter

3. One should practice more than one correct type questions from this chapter.

4. Various chemical phenomena like electrophoresis must be understood with utmost sincerity.

## Books prescribed:

First, you must finish the class XII NCERT textbook and solve each and every example and unsolved question given in it. Then for advanced level preparation like JEE and NEET, you must follow R.C. Mukherjee and P.Bahadur. You must definitely solve the previous year papers. Meanwhile, in the preparation, you must continuously write the mock tests for the depth of knowledge. Our platform will help you to provide with the variety of questions for deeper knowledge with the help of videos, articles and mock tests.

## Chemistry Chapter- wise Notes for Engineering and Medical Exams

 Chapters No. Chapters Name Chapter 1 Some basic concepts in chemistry Chapter 2 States of matter Chapter 3 Atomic Structure Chapter 4 Solutions Chapter 5 Chemical Thermodynamics Chapter 6 Equilibrium Chapter 7 Redox Reaction and Electrochemistry Chapter 8 Chemical kinetics Chapter 10 General Principle and processes of Isolation of metals Chapter 11 Classification of Elements and Periodic table Chapter 12 Hydrogen Chapter 13 p- block Elements Chapter 14 s-block Elements (Alkali and Alkaline Earth Metals) Chapter 15 Chemical Bonding and Molecular Structure Chapter 16 d- and f- BLOCK ELEMENTS Chapter 17 Coordination Compounds Chapter  18 Environmental Chemistry Chapter 19 Purification and Characterisation of Organic Compounds Chapter 20 Some Basic Principles of Organic Chemistry Chapter 21 Hydrocarbons Chapter 22 Organic Compounds containing Halogens Chapter 23 Organic Compounds containing Oxygen Chapter 24 Organic Compounds Containing Nitrogen Chapter 25 Polymers Chapter 26 Biomolecules Chapter 27 Chemistry in Everyday Life Chapter 28 Principles Related to Practical Chemistry

### Topics from Surface Chemistry

• Adsorption ( JEE Main ) (22 concepts)
• Physisorption and chemisorption and their characteristics ( JEE Main ) (11 concepts)
• adsorption from solutions ( JEE Main ) (1 concepts)
• Catalysis - Homogeneous and heterogeneous ( JEE Main ) (8 concepts)
• colloids and suspensions ( JEE Main ) (8 concepts)
• multimolecular, macromolecular and associated colloids (micelles) ( JEE Main ) (1 concepts)
• preparation and properties of colloids - Tyndall effect, Brownian movement, electrophoresis, dialysis, coagulation and flocculation ( JEE Main ) (5 concepts)
• Colloidal state- distinction among true solutions ( JEE Main ) (8 concepts)
• activity and selectivity of solid catalysts ( JEE Main ) (1 concepts)
• Emulsions and their characteristics ( JEE Main ) (1 concepts)
• INTRODUCTION TO SURFACE CHEMISTRY ( JEE Main ) (1 concepts)
• ADSORPTION AND ABSORPTION ( JEE Main ) (8 concepts)
• COLLOIDS ( JEE Main ) (18 concepts)
• CATALYSIS ( JEE Main ) (5 concepts)

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