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Surface Chemistry Chapter - Chemistry JEE Main

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Concepts of Surface Chemistry for JEE Main Chemistry

A study of a physical and chemical phenomenon that occurs at the interface of two phases including solid-liquid interface, solid-gas interface, liquid-gas interface, and the solid-vacuum interface is surface chemistry. Some of the related practical applications of Surface Chemistry are classified as surface engineering. Surface chemistry encompasses the concept such as semiconductor device fabrication, heterogeneous catalyst, fuel cells, self-assembled monolayers, and adhesives. Surface chemistry is said to be closely related to colloidal science and interface. Physics and interfacial chemistry are common subjects for both, but the methods are different. The colloidal and interface science studies microscopic phenomena that occur in heterogeneous systems due to the particularity of interface. 

What is Surface Chemistry?

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Roughly if we define the surface chemistry then it can be defined as the study of chemical reactions at interfaces. Surface chemistry is very much related to surface engineering which aims at modifying the chemical composition of the surface by the incorporation of the selected elements or the functional groups that produce various desired effects or improvement in the properties of the interface or the surface. Electrochemistry overlaps with surface chemistry. To the field of the heterogeneous catalyst, surface chemistry is of particular importance.

The addition of gas or liquid molecules to the surface is known as adsorption, this can be either due to chemisorption or by physio absorption. These two are included in surface chemistry. 

History and Chemistry

Heterogeneous catalyst, the field with which the surface chemistry started with pioneered by Paul Sabatier , Fritz Haiber on the Haber process. Irving Langmuir was also known as one of the founders of this field and the scientific generals on the surface of science. The Langmuir adsorption equation is used to model monolayer adsorption where all surface absorption sites have the same affinity for the adsorbing species and do not interact with each other. In 1947, Gerhard Ertl described for the first time the adsorption of hydrogen on the palladium surface by using a novel technique called LEED.

Similar studies are done with nickel, platinum and iron. Most of the recent development in the surface science includes the 2007 Nobel prize winner of Chemistry Gerhard Ertl’s advancements in surface chemistry, especially his interaction or investigation between carbon monoxide molecules and platinum surface.
The study of the phenomenon occurring on the surface of two substances is known as surface chemistry. This is very applicable in the day to day life and industrial use also.

In other words we can say that Surface Chemistry deals with all the other surface phenomena. 

Analysis Techniques

The study of surface analysis techniques involves both physical and chemical analysis techniques. Several methods that are modern probe the topmost that is 1-10 nm of surface exposed to vacuum. These involve X-ray photoelectron spectroscopy (XPS), angle-resolved photoelectron spectroscopy, low energy electron diffraction, thermal desorption spectroscopy, ion scattering spectroscopy, secondary ion mass spectrometry, dual-polarization interferometry, and other surface analysis methods included in the list of material analysis methods.

Vacuum is required for many of these techniques as they rely on the detection of electrons or ions as emitted from the surface under study. Ultra-high vacuum in general, is necessary to reduce surface combination. For the study of the interface, purely optical techniques can be used under a wide range of conditions.

Dual polarization interferometry, reflection-absorption infrared, surface-enhanced Raman spectroscopy, and some of the frequency generation spectroscopy can be used to probe solid-vacuum as well as solid-gas, and liquid-gas surfaces. Surface plasmon resonance which is of multi-parametric surface works in the solid-gas, solid-liquid, liquid-gas surfaces and can even detect the sub nanometric layers. 

Applications

In the era of modern industrialization, Surface Chemistry plays a very important role in various industrial techniques for chemical and energy conservation, information processing, material, environmental protection, health care, etc. The paramount importance of Surface Chemistry is reflected in the tremendous economic impacts made by these technologies. In several major industries, the role of Surface Chemistry is important. Technological development is a further challenge for Surface Chemistry

A catalyst’s work is to accelerate a chemical reaction without being consumed in the process. This is the role of a catalyst. For multiple processed products, in the chemical reaction a catalyst may promote the production of a specific product, which is referred to as the selectivity of the catalyst. The heterogeneous chemical reactions occur on the surface of solid catalysts and involve elementary surface chemical processes such as the reaction of adsorbed species and surface diffusion and desorption of the reaction products. The chemical reactions acceleration is due to the higher reactivity of the surface atoms that facilitates bond breaking and bond rearrangement of the adsorbed molecules. In 1800, the large-scale synthesis of important but simple bulk chemicals including ammonia, nitric acid, sulphuric acid, was the first industrial process based on heterogeneous catalysts


JEE Main Chemistry Chapters 2024

Adsorption: Physisorption and Chemisorption

Adsorption is a crucial phenomenon in surface chemistry, vital for various applications. It can be broadly categorized into physisorption and chemisorption.


Physisorption:

Physisorption is a physical adsorption where weak van der Waals forces hold gas or liquid molecules onto a solid surface. It's a reversible process involving a weak interaction between the adsorbate and the adsorbent. The adsorbate accumulates on the surface due to attractive forces without undergoing any chemical change. Physisorption occurs at relatively low temperatures and is affected by factors like surface area and temperature.


Chemisorption:

Chemisorption, on the other hand, involves a chemical reaction between the adsorbate and the surface atoms of the adsorbent. Covalent or ionic bonds form between the adsorbate and the surface, leading to a stronger and more stable attachment. Chemisorption typically occurs at higher temperatures and is specific to the nature of the adsorbate and adsorbent.


Factors Affecting Adsorption of Gases on Solids: Freundlich and Langmuir Adsorption Isotherms

Adsorption of gases on solid surfaces depends on several factors, including temperature, pressure, surface area, and the nature of both the adsorbate and the adsorbent. Freundlich and Langmuir adsorption isotherms are essential tools to understand the relationship between adsorbate concentration and adsorption.


Freundlich Adsorption Isotherm:

\[\frac{x}{m} = k_1P^{1/n}\]

The Freundlich isotherm describes multilayer adsorption on heterogeneous surfaces. Here, 

(x) is the amount of gas adsorbed per unit mass of the adsorbent, 

(P) is the pressure of the gas, 

$(k_1)$ is the adsorption equilibrium constant, and 

(n) is the Freundlich constant.


Langmuir Adsorption Isotherm:

\[\frac{x}{m} = \frac{k_2P}{1 + k_2P}\]

The Langmuir isotherm assumes monolayer adsorption on a homogeneous surface. 

(x) represents the amount of gas adsorbed, 

(P) is the pressure of the gas, 

$(k_2)$ is the Langmuir constant, and 

(m) is the mass of the adsorbent.


Adsorption from Solutions:

Adsorption from solutions involves the accumulation of solute molecules on the surface of a solid adsorbent. The process is influenced by factors like solute concentration, temperature, and surface properties of the adsorbent.


How Absorption can Be Distinguished from Adsorption?

S.No. 

Absorption 

Adsorption 

1.

The process of absorption is a property of bulk matter as it deals with the matter as a whole.


(Particles are uniformly present throughout the bulk matter)


The process of adsorption mainly takes place on the surface of the matter and hence it is termed a surface phenomenon. 


(Concentration of the particles at the surface is more than the bulk matter)


2. 

The absorbed substance is assimilated uniformly throughout the matter of the substance.

The adsorb substance is accumulated at the surface of the adsorbent only.

3. 

Absorption takes place at a constant rate.

The initial rate of adsorption is rapid. The rate however decreases gradually till the equilibrium is attained.

4. 

Energy is absorbed during this process.

Energy is given out in this process.

5. 

No visible effect of temperature on the process of absorption.

Low temperature facilitates the process of adsorption.

 

Types of Adsorption

The understanding of the nature of forces existing between the adsorbate and the adsorbent molecules helps us to classify the process of adsorption in the following two types:


  • Physical Adsorption 

  • Chemical Adsorption

                           

S.No.

Physical Adsorption 

Chemical Adsorption

1.

Weak van der Waals intermolecular forces exist between adsorbent and adsorbate.

It is characterized by chemical bond formation.

2.

It is a reversible process that is not dependent on the specific nature of molecules.

It is an irreversible process and is dependent on the specific nature of molecules.

3.

Gases that do not undergo compound formation with the adsorbent exhibit physical adsorption.

Gases that undergo compound formation with the adsorbent exhibit chemisorption.

4.

The heat evolved during physical adsorption is low and is negative.

The heat evolved during chemical adsorption is high and is negative.

5.

Low temperature favours physical adsorption. So, on supplying external heat its rate decreases.

High temperature favours the rate of chemical adsorption, especially in endothermic processes. So, on supplying external heat, the rate of adsorption increases.

6.

External activation energy is not required.

High external activation energy is required for chemisorption to take place.

7.

High pressure allows the particle to adsorb on the surface. Decrease of pressure causes desorption.

High pressure facilitates ease of chemisorption. However, a decrease in pressure does not cause desorption.

9.

The formation of multi-layers on adsorbent surfaces under high pressure is visible.

Formation uni-molecular layer is observed during chemisorption.

10. 

It is also known as physisorption. 

It is also known as chemisorption. 

11. 

For physisorption, the enthalpy of adsorption is low. 

For chemisorption, the enthalpy of adsorption is high. 

 

Catalysis: Homogeneous and Heterogeneous

Catalysis accelerates chemical reactions without being consumed in the process. It can be homogeneous or heterogeneous based on the phase of the catalyst concerning the reactants.


Homogeneous Catalysis:

In homogeneous catalysis, the catalyst is in the same phase as the reactants. It involves the formation of intermediate complexes and is widely seen in solution-phase reactions. Coordination compounds often act as homogeneous catalysts, speeding up reactions in organic and inorganic chemistry.


What is Homogeneous Catalysis and Catalyst? 

The catalyst that is present in the same phase as the reactants in the reaction is called homogeneous catalyst and this type of catalysis process is called homogeneous catalysis. 


Examples of Homogeneous Catalysis and Catalysts – 

  1. Hydrolysis of Sugar – In the hydrolysis of sugar reactants sugar (sucrose solution) and water are used in liquid states and the catalyst sulfuric acid is also used in the liquid state. The reaction is given below –

C12H22O11(l) + H2O(l) H2SO4(l)→ C6H12O6(l) + C6H12O6(l)

Sucrose                                            Glucose      Fructose

  1. Hydrolysis of the Ester – In the hydrolysis of the ester, the ester is taken in a liquid state with water (liquid) for the reaction in presence of catalyst hydrochloric acid which is also taken in a liquid state. The reaction is given below –

CH3COOCH3(l) + H2O(l) HCl(l)→ CH3COOH(l) CH3OH(l)


Heterogeneous Catalysis:

Heterogeneous catalysis occurs when the catalyst is in a different phase from the reactants. Solid catalysts, often metals or metal oxides, play a significant role in heterogeneous catalysis. They provide active sites where reactant molecules can bind, leading to increased reaction rates. Heterogeneous catalysis is widely used in industrial processes, including the production of ammonia and petroleum refining.


What is Heterogeneous Catalysis and Catalysts? 

The catalyst whose phase differs from that of the reactants in the reaction is called heterogeneous catalyst and this type of catalysis process is called heterogeneous catalysis. 

 

Examples of Heterogeneous catalysis and catalysts – 

  1. In Haber’s process of formation of ammonia, nitrogen and hydrogen are used in gaseous forms while catalyst iron is used in solid form. 

N2(g) + 3H2(g) Fe(s)→ 2NH3

  1. Formation of Sulfuric Acid – In this process sulfur dioxide (gas) is oxidized to sulfur trioxide (gas) by heterogeneous catalysis in presence of a solid V2O5 catalyst. Then sulfur trioxide is hydrolyzed to sulfuric acid. 

SO2(g) + O2(g) V2O5(s)→ 2 SO3(g)


Activity and Selectivity of Solid Catalysts:

Catalyst activity refers to the ability to enhance the reaction rate, while selectivity denotes the ability to direct the reaction toward specific products. Catalysts are often designed or modified to improve both these aspects, ensuring high efficiency and desired outcomes in chemical processes.


What is Adsorption Theory of Heterogeneous Catalysis? 

Modern Adsorption theory of heterogeneous catalysis is the mixture of moderate compound hypothesis and the old adsorption hypothesis or old adsorption theory. Old adsorption theory lacked specificity so there was a need for modern adsorption theory. 

 

According to the adsorption theory of heterogeneous catalysts, there are free valances in the catalyst on which reactant molecules get attached. The mechanism of the adsorption theory of heterogeneous catalysis involves the following steps –


  • Step 1. Diffusion of reactant molecules 

  • Step 2. Adsorption 

  • Step 3. Intermediate complex formation 

  • Step 4. Desorption 

  • Step 5. Diffusion of product molecules 


Step 1. Diffusion of Reactant Molecules – In this step reactant molecules get diffused towards the surface of the catalyst. 

 

Step 2. Adsorption – In this step reactant molecules get adsorbed on the surface of the solid catalyst or form loose bonds with the free valencies of the catalyst. 

 

Step 3. Intermediate Complex Formation – In this step adsorbed reactant molecules on the surface of the catalyst react with each other and form new stronger bonds with each other which leads to the formation of an intermediate. 

 

Step 4. Desorption – In this step intermediate converts into the product as it loses its affinity towards the catalyst. The product molecule gets desorbed from the surface of the catalyst. 

 

Step 5. Diffusion of Product Molecules – In this step desorbed product molecules from the surface of the catalyst gets diffused away from the catalyst. 


What is Shape Selective Catalysis by Zeolites? 

Shape selective catalysis is that type of catalysis which depends upon the pore structure of the catalyst and the size of the reactant and product molecules. Zeolite is a porous solid made up of silicon, aluminium and oxygen and a good shape-selective catalyst. It has cavities in its structure where ions or atoms or small molecules can reside. 


What is Enzyme Catalysis? 

Many enzymes also act as catalysts for many reactions. As enzymes catalyze many reactions which occur in our body, plants and animals. So, they are known as biochemical catalysts and the phenomenon is called biochemical catalysis. 


Characteristics of Enzyme Catalysis 

  • Highly efficient 

  • Very specific nature 

  • They perform best at optimum temperature and optimum pH

  • The activity of enzymes is increased in the presence of activators and coenzymes

  • Inhibitors can destroy or reduce the activity of enzymes 


Enzyme Catalysis and Its Mechanism:

Enzymes are biological catalysts crucial for life processes. They are highly specific and speed up biochemical reactions inside living organisms. Enzyme catalysis involves the formation of enzyme-substrate complexes, lowering the activation energy required for the reaction. Enzymes facilitate reactions in cells, ensuring metabolic pathways function efficiently.


Colloidal State: Distinction and Classification

Distinction Among True Solutions, Colloids, and Suspensions:

True Solutions: These are homogeneous mixtures at the molecular level, where solute particles are completely dissolved and cannot be distinguished under a microscope.


Colloids: Colloids are heterogeneous mixtures with dispersed particles larger than molecules but small enough not to settle rapidly. They exhibit the Tyndall effect, where light is scattered as it passes through the colloid.


Suspensions: Suspensions contain larger particles than colloids and can be observed with the naked eye. Unlike colloids, suspended particles settle over time due to gravity.


Classification of Colloids:

Colloids are classified based on the nature of the interaction between the dispersed phase and the dispersion medium.


Lyophilic Colloids: Also known as solvent-loving colloids, these have a strong affinity for the dispersion medium. The particles disperse readily, forming stable colloidal systems.


Lyophobic Colloids: Lyophobic colloids, or solvent-repelling colloids, do not have a strong affinity for the dispersion medium. They require the addition of a stabilizing agent to prevent coagulation.


Difference between Lyophilic and Lyophobic Sols 

S. No. 

Lyophilic Sol 

Lyophobic Sol 

1.

In these sols, the dispersion phase has a strong affinity for the dispersion medium. 

In these sols, the dispersion phase has very less or no affinity for the dispersion medium. 

2.

They are more stable. 

They are less stable.

3.

They are reversible.

They are irreversible. 

4.

Colloidal particles have no charge. 

Colloidal particles carry either positive or negative charges. 

5.

They need no stabilizers during preparation.

They need stabilizers during preparation. 

6.

They are solvent loving colloids. 

They are solvent hating colloids.

7.

They are highly viscous sols.

They possess the same viscosity as the solvent. 

8.

When water is taken as a solvent, it is called hydrophilic sol. 

When water is taken as a solvent, it is called the hydrophobic solvent. 

9. 

Examples – Starch sol, egg albumin sol etc. 

Examples – Ferric hydroxide sol, aluminium hydroxide sol etc. 

 

Multimolecular Colloids: These colloids consist of aggregates of small molecules, forming clusters or micelles in the dispersion medium.


Macromolecular Colloids: Macromolecular colloids are large molecules like proteins, starch, or synthetic polymers dispersed in the medium.


Associated Colloids (Micelles): Micelles form when surfactant molecules aggregate in a solution, creating structures with a hydrophilic outer layer and a hydrophobic inner core.

Based on the physical state of the dispersed phase and dispersion medium – Colloids can be divided into 8 types based on the physical state of the dispersed phase and dispersion medium. All eight types of colloids are listed below –


Types of colloid 

Dispersed phase 

Dispersing medium 

Aerosol 

Liquid 

Gas 

Aerosol 

Solid 

Gas 

Foam 

Gas 

Liquid 

Emulsion 

Liquid 

Liquid 

Sol 

Solid 

Liquid 

Solid sol 

Gas 

Solid 

Gel 

Liquid 

Solid 

Solid sol 

Solid 

Solid 


Preparation of Colloids 

Colloids can be prepared by the following methods –


  • Chemical Methods – Double decomposition, hydrolysis, oxidation and reduction are the various chemical reactions that are used in the preparation of colloids through chemical methods. 

Example – SO2 + 2H2S Double decomposition→ 3S + 2H2

  • Electrical Disintegration or Bredig’s Arc Method – In this method metal electrodes are immersed in the dispersion medium and intense heat is produced which converts the metal into vapour. The vapour of metal gets condensed into particles of colloidal size. Example – gold sol, silver sol etc. 

  • Peptization – Peptization is the process of converting a precipitate into colloidal sol by shaking it with a dispersion medium in the presence of a small amount of electrolyte. The electrolyte used for this purpose is called a peptizing agent.

  • Purification of Colloidal Solution – Colloidal solutions generally contain some impurities like an extra amount of electrolytes etc. The process used for reducing the number of impurities to a requisite minimum is known as the purification of colloidal solution. Dialysis, electrodialysis, ultrafiltration are the main methods that are used in the purification of colloids. 

 

Applications of Colloids 

Colloids have various applications in many fields. Some uses of colloids are listed below –


  • Colloids are used in the foods and food industries at a large level. Many foods which we consume are colloidal. Such as milk, cheese etc. 

  • Colloids have various applications in the medicinal field as well. Many medicines which we use are in the form of emulsions. Antibiotics such as penicillin and streptomycin are given in the form of colloidal solutions so that they can be absorbed by the human body easily. 

  • Colloids are used in water purification. 

  • Sewage water contains impurities like dirt, stool, urine etc. which are dispersed in water. Thus, forms a colloidal system. These can be removed by electrophoresis. 

  • Smoke is also a colloidal system of carbon particles in the air. This can also be purified by electrophoresis. 

  • These are used in artificial rain as well. 

  • Rubber is obtained by a colloidal solution called latex through coagulation. 

  • Treatment of the skin of animals to get leather is called tanning. In the process of tanning, colloids are used. 


Examples of Colloids 

We see many colloidal solutions around us. Many food items such as cake, milk, bread, butter, ice cream fruit juices, whipped cream etc. are examples of colloids. Apart from these fog, mist clay etc. are also examples of colloids. We are providing a list of examples of colloids with their dispersed phase and dispersing medium below –


Dispersed Phase 

Dispersing Medium 

Examples 

Liquid 

Gas 

Fog, mint 

Solid 

Gas 

Smoke, automobile exhaust 

Gas 

Liquid 

Shaving cream 

Liquid 

Liquid 

Milk 

Solid 

Liquid 

Mud 

Gas 

Solid 

Foam, rubber 

Liquid 

Solid 

Jelly, butter 

Solid 

Solid 

Garnet, citrine 

 

Properties of Colloids 

Colloids show the following properties –


  • It is a heterogeneous mixture. 

  • The size of colloidal particles is very small. Their particle size ranges between 1-1000 nanometers. 

  • It shows a Tyndall effect. It means it scatters the beam of light and shows its path through itself. 

  • They don’t settle down when left undisturbed for some time. it means colloidal solutions are quite stable. 

  • They cannot be separated by a filtration process. 

  • They can be separated by centrifugation. 

  • Colloidal particles show Brownian movement


1. Tyndall Effect:

The Tyndall effect is the scattering of light by colloidal particles. When a beam of light passes through a colloidal solution, it becomes visible due to the scattering of light by the dispersed particles. This phenomenon is employed in fields like optics and is a useful tool to distinguish between colloids and true solutions.


2. Brownian Movement:

Brownian movement refers to the random and continuous motion exhibited by colloidal particles when suspended in a liquid medium. This erratic movement results from the particles' collision with solvent molecules. Brownian motion plays a vital role in various colloidal applications and is a fundamental aspect of colloid science.


3. Electrophoresis:

Electrophoresis is the movement of charged colloidal particles in an electric field. The particles migrate towards the electrode of opposite charge. This property is used in various laboratory techniques for separating and analyzing colloidal particles based on their charge and size. Electrophoresis is critical in fields like biochemistry and biotechnology.


4. Dialysis:

Dialysise is the process of separating colloidal particles from ions or smaller molecules using a semipermeable membrane. The colloidal solution is placed in a bag or tube made of the dialyzing membrane, and solvent molecules and small ions pass through the membrane, leaving behind the colloidal particles. Dialysis is used for purifying and concentrating colloidal dispersions.


5. Coagulation and Flocculation:

Coagulation and flocculation are processes that destabilize colloidal dispersions by inducing the aggregation of colloidal particles. Coagulation results in irreversible clumping of particles, while flocculation forms loosely aggregated structures. These processes are often employed in water treatment and wastewater purification to facilitate the removal of colloidal impurities.


6. Emulsions and Their Characteristics:

Emulsions are colloidal systems consisting of two immiscible liquids, typically an oil and water, where one liquid is dispersed as small droplets in the other. Emulsifying agents, often known as surfactants or emulsifiers, are added to prevent the separation of the two liquids. Emulsions have distinct characteristics:


Stability: Emulsions can be either stable or unstable, depending on the balance between attractive and repulsive forces among the dispersed droplets. Stable emulsions resist separation over time.


Examples: Common examples of emulsions include milk (an oil-in-water emulsion) and mayonnaise (a water-in-oil emulsion).


Applications: Emulsions are widely used in various industries, including food and cosmetics, for products like salad dressings, creams, lotions, and more.


What is Emulsification?

Emulsification is the process of creating an emulsion. It involves mixing the two immiscible liquids together in a way that breaks up the droplets of the dispersed phase into very small droplets that are stable and do not coalesce. Emulsification can be carried out using a variety of methods, including mechanical agitation, high-shear mixing, and the use of emulsifiers. 


Appearance: Can vary depending on the method used

Stability: Can be unstable if not properly emulsified

Examples: Mixing oil and water with an emulsifier, using a high-shear mixer

Note: All emulsions are a result of emulsification, but not all mixtures of two immiscible liquids are emulsions.


Mechanism of Emulsification

Many different chemicals and physical processes and mechanisms can be involved in the process of emulsification. The mechanism of emulsification can be based on the following three theories –


Surface Tension Theory – According to surface tension theory, emulsification takes place by the reduction of interfacial tension between the dispersed phase and the dispersion medium. 


Repulsion Theory – According to repulsion theory repulsion force between the particles of the dispersed phase cause them to remain dispersed in the dispersion medium. The emulsifying agent makes a film over one phase which makes globules of that phase and these globules repel each other. 


Viscosity Modifications – Some emulsifying agents increase the viscosity of the medium. Due to an increase in the viscosity of the medium, globules of the dispersed phase remain dispersed in the dispersion medium. 


Properties of Emulsions 

Properties of emulsions are listed below –


  • Emulsions contain both a dispersed phase and a dispersion medium.

  • The boundary between the dispersion phase and dispersed medium is called “interface”. 

  • They have a cloudy appearance.

  • They show various colours depending on the dilution. Such as, the emulsion appears white if it scatters the light equally. If it is diluted it will appear blue while if it is concentrated, then it will appear yellow. 

  • It shows the Tyndall effect. 

  • The particle size of a dispersed phase in emulsions may vary.

  • Generally, emulsions are inherently unstable, exposure to energy and power ultrasound is needed to form a stable emulsion.

  • Emulsion particles form dynamic inhomogeneous structures on a small length scale. 

  • Both the phases of emulsion may get separated If it is kept undisturbed for a longer period or in absence of an emulsifying agent. 


Types of Emulsions 

Broadly, Emulsions can be divided into two types –


  • Simple Emulsions 

  • Complex Emulsions 


Simple Emulsions – Simple emulsions are those emulsions that are formed by either dispersing oil in water or water in oil. Simple emulsions can be divided into the following two types –


  • Water in oil emulsion 

  • Oil in water emulsion 


Water in Oil Emulsion – If the dispersed phase is water and the dispersion medium is oil in the emulsion, then these types of emulsions are called water in oil emulsions. It is also called W/O types of emulsions. 


In these types of emulsions, water is an internal phase and oil is an external phase. Cold cream, butter etc. are examples of water in oil emulsions.

 

Oil in Water Emulsion – If the dispersed phase is oil and the dispersion medium is water in the emulsion, then these types of emulsions are called oil in water emulsions. It is also called O/W types of emulsions.


Complex Emulsions – Complex emulsions are also called multiple emulsions. In these types of emulsions, a complex system exists in which both oils in water and water in oil emulsion exist together and are stabilized by surfactants. These can be divided into the following types –


Water - in – oil – in - water emulsion

Oil – in – water – in – oil emulsion  


Water - in – Oil – in - Water Emulsion – These are also called W/O/W emulsions. In these types of emulsions oil droplets enclosing water, droplets are dispersed in water. These are double emulsions of O/W emulsion and W/O emulsion. 


Oil – in – Water – in – Oil Emulsion - These are also called O/W/O emulsion. In these types of emulsions water droplets enclosing oil, droplets are dispersed in the oil phase. These are double emulsions of O/W emulsion and W/O emulsion. 


This ends our coverage on the summary of the unit “Surface Chemistry”. We hope you enjoyed learning and were able to grasp the concepts. You can get separate articles as well on various subtopics of this unit such as what is adsorption? Colloids, Emulsions etc. on the Vedantu website. We hope after reading this article you will be able to solve problems based on the topic. We have already provided detailed study notes or revision notes for this unit, which you can easily download by registering yourself on the Vedantu website. Here in this article, we have discussed the unit in a summarized way with an emphasis on important topics of the unit.  If you are looking for solutions to NCERT Textbook problems based on this topic, then log on to the Vedantu website or download Vedantu Learning App. By doing so, you will be able to access free PDFs of NCERT Solutions as well as Revision notes, Mock Tests and much more.


Emulsifying Agents Examples and Significance

Some of the emulsifying agent example are:


  1. Lecithin: This phospholipid, found in egg yolks and soybeans, exhibits both hydrophilic and hydrophobic properties, making it an effective emulsifying agent.

  2. Sodium Stearoyl Lactylate (SSL): This synthetic emulsifier is commonly used in food products, particularly in ice cream and baking mixes, to enhance stability and prevent syneresis.

  3. Monoglycerides and Diglycerides: Derived from fats and oils, these molecules possess both hydrophilic and hydrophobic properties, enabling them to stabilize emulsions effectively.

  4. Gum Arabic: This natural gum, obtained from the acacia tree, is a hydrophilic colloid that acts as an excellent emulsifier due to its ability to form a protective film around dispersed droplets.

  5. Carrageenan: Extracted from seaweed, carrageenan is another hydrophilic colloid that serves as a potent emulsifier, particularly in dairy products like yogurt and cheese.

  6. Xanthan Gum: Produced by the fermentation of glucose, xanthan gum is a hydrophilic colloid that enhances emulsion stability due to its ability to form a network around dispersed droplets.

  7. Agar-agar: Derived from red seaweed, agar-agar is a hydrophilic colloid with excellent emulsifying properties, often used in desserts and confectionery products.

  8. Soaps and Detergents: These amphiphilic molecules, containing both hydrophilic and hydrophobic regions, facilitate emulsion formation by reducing interfacial tension and preventing droplet coalescence.

  9. Proteins: Certain proteins, such as casein and whey protein, can act as emulsifiers due to their ability to form complexes with both oil and water molecules.

  10. Starches: Modified starches, such as acetylated distarch adipate (ADA), can act as emulsifiers by forming a protective film around dispersed droplets and preventing phase separation.


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JEE Main Surface Chemistry Study Materials

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JEE Main States of Matter Practice Paper


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Conclusion

In this article, we'll dive into the world of Surface Chemistry, a crucial topic for JEE Main. We'll explore its fundamental concepts, problem-solving strategies, and key insights. You can expect to grasp the essential principles of this topic and find solutions to common questions. Our goal is to make sure all the information you need is conveniently accessible in one place. Students can freely access PDFs containing explanations, definitions, and practice questions. This comprehensive resource will significantly aid you in your exams, ensuring a strong understanding of Surface Chemistry.

FAQs on Surface Chemistry Chapter - Chemistry JEE Main

1. In Surface Studies Why is it Important to have a Clean Surface?

It is necessary to have a clean surface as it facilitates the adsorption of the desired gases. If the surface is covered by the film of air then it will not be available for adsorption of the desired gases. Therefore, it is very important to have a clean surface in the surface studies, which is the study in surface chemistry. 

2. Why is the Adsorption Reaction always Exothermic?

The adsorption reaction is always exothermic because when gas is adsorbed on a solid surface, immediately it’s movement is restricted leading to a decrease in the entropy of the gas. For a process to be spontaneous,G should be negative. Here, S is negative, so H has to be negative to make G negative, so adsorption is always exothermic.

3. What is the Role of Desorption in the Process of Catalysis?

The role of desorption in the process of catalysis can be defined as the phenomenon where a substance is released from or through the surface, it is opposite of the sorption process. Desorption helps in the catalyst to make it free for the next reaction. 

4. What is Emulsification?

Emulsification is a process in which two immiscible liquids are mixed together to form a stable dispersion of one liquid in another. In other words, it is the process of creating a suspension of tiny droplets of one liquid (the dispersed phase) in another liquid (the dispersion medium). The dispersed phase droplets are typically much smaller than the size of the dispersion medium molecules.

5. What are the key topics covered in the Surface Chemistry chapter for JEE Main Chemistry?

The Surface Chemistry chapter in JEE Main Chemistry includes topics such as adsorption, catalysis, colloids, and Langmuir adsorption isotherm, offering a comprehensive understanding of surface phenomena.

6. How can Vedantu help in mastering the Surface Chemistry chapter for JEE Main preparation?

Vedantu provides expert guidance, personalized learning, and interactive sessions focused on Surface Chemistry. With access to practice materials and flexible scheduling, students can reinforce their understanding and excel in JEE Main Chemistry.