Important Terms In Surface Chemistry

Surface Chemistry 

 

Surface Chemistry 

Surface chemistry refers to the study of chemical processes that occur at the surfaces or interfaces of materials, such as solids, liquids, or gases. This includes phenomena such as adsorption, desorption, catalysis, corrosion, and oxidation that happen at the boundary between two phases.

Importance:

As a result of the critical roles that surface and interface play in several applications, such as catalysis (chemical reactions), corrosion of materials, electrochemistry, adhesion, lubrication, heterogeneous mixture, and purification procedures, among others, surface chemistry is significant in the field of chemistry. Scientists can create novel materials with desired features and enhance the effectiveness of many industrial processes by better understanding the mechanics and characteristics of surface chemistry. To create efficient products and procedures, many sectors, including biotechnology, electronics, medicine, energy, chemical manufacture, and environmental cleanup, rely on a thorough grasp of surface chemistry fundamentals.

Absorption:

Phenomena of absorption involve the transfer of matter or energy from an external medium into another medium. For example, in the process of absorption, a substance (the adsorbate) is transferred from one fluid or solid phase into another (the adsorbent), often resulting in the adsorbate being held or bound onto the surface of the adsorbent. This process can be influenced by various factors including temperature, pressure, time, surface area, and the physical and chemical properties of the adsorbate and adsorbent.

Types of Absorption:

There are various types of absorption, including:

A. Physical absorption:

This is the reversible process of gases and vapors being taken up into or adsorbed onto the surface of a solid or liquid.

B. Chemical absorption:

This is a process where a substance reacts with a solute to form a new compound. 

C. Molecular absorption: 

This is the process where the energy of a photon or radiant energy is absorbed by a molecule, leading to an increase in its internal energy.

D. Biological absorption:

This is the process by which living organisms absorb nutrients and other materials in order to carry out their metabolic functions. 

E. Sound absorption: 

This is the process where sound waves are absorbed by a material and converted into heat or other forms of energy.

Adsorbate and Adsorbent:

Adsorbate refers to the substance being adsorbed, while adsorbent refers to the material on which the adsorption occurs. 

Desorption:

Desorption is the process in which an adsorbed substance is released from an adsorbent material. It can occur naturally or be induced through external stimuli (e.g., heating). 

Sorption:

Sorption is a general term that refers to both adsorption and desorption, the process of attachment and detachment of molecules onto materials. 

Adsorption Isotherm:

Adsorption isotherm refers to the relationship between the amount of a gas or liquid adsorbed onto a solid surface and its equilibrium pressure or concentration. There are several types of absorption isotherms which are commonly used in surface chemistry research. These include:

A. Langmuir Isotherm: 

This is one of the most commonly used isotherms to describe adsorption of a gas onto a solid surface. It assumes that there are a limited number of adsorption sites on the surface of the solid, and that the adsorption of gas molecules onto these sites follows an equilibrium process. The Langmuir equation is expressed as Q = QmKc / (1 + Kc), where Q is the amount of adsorbate on the surface, Qm is the maximum amount that can be adsorbed and Kc is a constant related to the affinity of the adsorbate for the surface.

B. Freundlich Isotherm: 

The Freundlich isotherm is often used for heterogeneous surfaces where there is no specific adsorption site. It assumes that there is a certain degree of adsorption on all surface areas. This isotherm is expressed as Q = Kc^(1/n), where Q is the amount of adsorbate on the surface, K and n are constants related to the surface properties, and c is the concentration of adsorbate.

Overall, these absorption isotherms are essential in understanding how molecules are adsorbed on the surface of various materials, which contributes to the development of new materials and improved industrial processes.

Catalysis: 

Catalysis is a process in which a substance accelerates a chemical reaction without itself being consumed or changed. In surface chemistry, catalysis is the study of the surfaces of catalysts and the way they interact with reactant molecules to increase the rate of chemical reactions.

Colloids: 

Colloids are systems in which small particles are dispersed in a continuous medium. These particles are typically bigger than individual atoms or molecules but smaller than visible particles. Examples of colloids include milk, blood, and fog. In surface chemistry, the study of colloids includes the behavior of particles at interfaces and the effects of surface chemistry on the stability and properties of colloidal dispersions.

Emulsion: 

The act of combining two immiscible liquids—typically, oil and water—to create an emulsion results in a stable composition. An emulsion is the end product, and it can be either an oil-in-water (O/W) or a water-in-oil (W/O) emulsion. The concepts of surface tension, interfacial tension, and the adsorption of surfactants and stabilizing agents at the interfaces of emulsifying systems are all included in the study of emulsions in surface chemistry.

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Emulsions, Adsorption and Adsorption Isotherm 

Zeolites, Catalysis, Colloids Properties

 Zeolites, Catalysis, Colloids Properties

Here we will discuss about,

Zeolites

Catalysis

Homogenous catalysis

Heterogenous catalysis

Enzyme catalysis

Shape selective catalysis by zeolites

Properties of colloids

Zeolites

By definition, a zeolite is a "boiling stone." This is due to the fact that they are stones with very high heat retention rates. They are incredibly porous and have the capacity to hold water, thus when heated, a lot of steam is released from their surface.

Commercial manufacturing of zeolites with specific structural and chemical characteristics allows for the exploitation of zeolite qualities. Hydrocarbon separation, such as in “the refinement of petroleum, drying of gases and liquids, and the prevention of pollution through selective molecule adsorption are a few examples of commercial usage”.

Natural zeolites are found as cavity fills in mafic volcanic rocks, most likely as a result of liquid or vapour deposition. They develop a wide variety of crystalline formations with enormously regular open holes. There are roughly 40 naturally occurring zeolites, and many artificial or synthetic zeolites have also been created.

The ability of their structure to contain other molecules is by far its most intriguing characteristic. They feature structures resembling honeycombs, which makes them effective shape-selective catalysts.

Due to structural and chemical variations, reversible dehydration and cation exchange are made possible by the framework's ease of ion and water movement. The type of dehydration differs depending on how the structure's water is bound.

Zeolite

Shape Selective Catalysis (ZEOLITES)

In shape-selective catalysis, catalysis and the molecular sieve effect are combined. Here, the shape or size of the reactant or substrate causes the catalyst to display preference or selectivity towards it. The size or form of the substrates and products, as well as the catalyst's pore structure, all affect these catalytic reactions. Zeolites are a good illustration of this kind of catalyst.

By transition state selectivity or by excluding competing reactants depending on their molecular size, they function as shape-selective catalysts. Reactant shape selectivity occurs when some of the reactant molecules are too big to diffuse into the zeolite pores. On the other hand, product shape selectivity occurs when only items with the right dimensions may diffuse out of the zeolite pores.

Zeolites, which are crystalline aluminosilicates, are the most popular molecular sieves utilised for catalytic applications. The Bronsted acid (proton)-containing zeolite pore shown in Figure, it is the catalytically active site for acid-catalyzed processes such aromatics alkylation with olefins. It has 10 tetrahedral atoms arranged in a ring. The silicate structure gains one negative charge when one tetrahedral Si (+4 in its oxidation state) is swapped out for one a-l-, (+3 in its oxidation state), which must be counterbalanced by a positive charge, often an alkali metal cation like Na.

Proton form zeolite can be produced by the subsequent ion-exchange with NH 4 or protonic acid, followed by heat treatment, as shown in Figure. In molecular sieve structures, partial substitution of tetrahedral Al or Si molecules by other atoms (such as Fe, Ga, etc.) can result in the formation of metallosilicates, which have recently discovered some significant catalytic uses.

Shape Selective Catalysis (ZEOLITES)

Catalysis

A "catalyst" is anything that helps to speed up a process; the word comes from the Greek letter v, which means "to annul," "to untie," or "to pick up."

"The prefix kata, which means "an intensifying prefix," Additionally λύω (lúō, "loosen")."

 Based on her innovative work in oxidation-reduction experiments, chemist Elizabeth Fulhame established the concept of catalysis and detailed it in a book in 1794. Gottlieb Kirchhoff, who discovered the acid-catalyzed conversion of starch to glucose, explored the first chemical process in organic chemistry to involve a catalyst in 1811. Later, in 1835, Jöns Jakob Berzelius coined the term "catalysis" to refer to processes that are sped up by components that do not change after the reaction. Prior to Berzelius, Fulhame conducted reduction experiments using water rather than metals.

Catalyst

Chemical reactions do not start because of a catalyst. The reaction does not use up a catalyst. As they react with reactants to produce intermediates, catalysts also help the final reaction product to be produced. A catalyst is capable of regeneration after the entire procedure.

Catalysts come in three different forms: solid, liquid, and gaseous. Metals or their oxides, such as halides and sulphides, are among the solid catalysts. As catalysts, semi-metallic substances including silicon, aluminium, and boron are also employed. The same is true for the employment of pure liquid and gaseous elements as catalysts. These substances are occasionally combined with the appropriate solvents or carriers.

A catalytic reaction is one in which their system contains a catalyst.

Types of Catalyst

Positive catalyst

Increase rate of reaction, for example, Iron oxide serves as a positive catalyst in Haber's process to create NH3, increasing the output of ammonia despite less nitrogen reacting with it.

Negative catalyst

Decrease the rate of reaction, for example, Acetanilide, which functions as a negative catalyst to slow down the rate of decomposition of hydrogen peroxide, retards the breakdown of hydrogen peroxide into water and oxygen.

Promoters

Increase the catalytic activity of catalyst, for example, Molybdenum or a combination of potassium and aluminum oxides function as Promoters in Haber's process.

Inhibitors

Decrease the catalytic activity of catalyst, for example, the catalyst palladium is poisoned with barium sulphate in quinolone solution to block the hydrogenation of alkyne to an alkene at the alkene level. The catalyst is also called the Lindler catalyst, used to prepare cis alkene from alkyne.

Homogenous catalysis

It is a type of catalysis in which physical state of reactant and catalyst are same.

Examples,

NO, H2SO4,Mno2 these are used as catalyst.

             

Homogenous catalysis

                 

Heterogeneous catalysis

Physical state of catalyst and reactant are different.

 

Examples,

Ni / pt and Fe act as catalyst.

     

Heterogeneous catalysis

                                            

Enzyme catalysis

The speeding up of a process by a biological molecule known as a "enzyme" is known as enzyme catalysis. The majority of these processes, including most enzymes, involve chemical reactions. Catalysis often takes place at a specific location inside the enzyme, known as the active site.

Proteins, either one protein chain or multiple chains in a multi-subunit complex, make up the majority of enzymes.

Properties of colloids

In nature, colloids are comparatively stable. The dispersed phase's particles continue to move continuously and are suspended in the solution. Colloids are referred to as heterogeneous in nature since they are made up of two phases, the dispersed phase and the dispersion medium. Colloids provide the impression of being a homogeneous solution even though they are heterogeneous in nature and comprise suspended particles. This is the case because the suspended particles are so small that the human eye cannot see them.

Ultrafilters, a type of specialized filter, are needed for filtration of colloids. They effortlessly filter through common filter papers without leaving behind any waste.

Brownian Motion of Colloids

The Brownian movement is a crucial characteristic of the scattered particles found in a colloidal solution. An ultramicroscope image of a colloidal solution reveals the colloidal particles to be moving continually in a zigzag pattern.

The colloidal particles are continuously attacked from all sides by the moving molecules of the dispersion medium. The Brownian movement gives the sol stability. It works against colloidal particles' gravitational pull and prevents them from settling, keeping the sol stable.

Tyndall Effect

The Tyndall effect, which is shown by colloids, was first noticed by Tyndall in 1869. A bluish light illuminates the path of the beam when it passes through a colloidal solution that has been kept in darkness. The 'Tyndall effect and Tyndall cone' are terms used to describe the phenomena of light scattering by colloidal particles. Dispersed colloidal particles cause emissions that are analogous to ultraviolet and visible radiations when light strikes them. These reflected rays are lighted.

Tyndall Effect

Colloidal solutions' electrical characteristics

The dispersion medium has an equal and opposite charge to that of the colloidal solution's particles, which all carry the same kind of charge. The solution as a whole is electrically neutral because the charge on the dispersion medium balances the charge on the dispersed particles.

A colloid's scattered particles oppose one another because they have identical electric charges, which keeps them from settling and preserves the sol's stability. The colloidal sols can be divided into positive and negative charged sols depending on the type of charge.

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Surface Chemistry

Colloidal chemistry, Colloids 

Emulsion, Adsorption and Adsorption Isotherm 

Emulsion, Adsorption, Adsorption Isotherm

 

Emulsion, Adsorption, Adsorption Isotherm 

Surface Chemistry

In general, the study of chemical interactions at interfaces is referred to as surface chemistry. It has a lot in common with surface engineering, which tries to alter the chemical composition of a surface by adding particular elements or functional groups that have specific intended effects or that enhance the qualities of the surface or interface. The disciplines of heterogeneous catalysis, electrochemistry, and geochemistry all benefit greatly from surface science.

You must have pondered how the particles in some types of liquids stay continuously sustained not settling down. What precisely takes place at the boundary between phases? Surface chemistry is the area of chemistry that studies the interactions between different phases, particularly those between liquid and gas. Surfaces actively participate in processes such as chromatography, electrode reactions, colloid creation, and catalysis.

Adsorption

Adsorption is the word used to describe the accumulation of species at higher concentrations on a substance's surface as a result of intermolecular force. For instance, activated charcoal may absorb gases like H2, O2, and N2.

Enthalpy of Adsorption is the quantity of heat energy released when one mole of gas is adsorbed on the surface area unit of an adsorbent.

Adsorption

Molecules attach on the surface of solid.

Absorption

Molecules moves into the surface of solids.

Desorption

Molecules moves out of the solid surface or removing molecules from adsorbent.

Adsorbate

Substance that adsorbed on the solid surface is called Adsorbate, for example gas adsorb on solid surface.

Adsorbent

It the surface where adsorption occur, for example solid surface where gas adsorb is called adsorbent.

Types of Adsorption

Adsorption in surface chemistry is divided into two categories based on the strength of the interaction between the adsorbent and the Adsorbate.

(A) Physical Adsorption

Physisorption, also known as physical adsorption. Between adsorbent and adsorbate, a weak van der Waals force is present.

It has following Characteristics:

1.      It has forces of Van der Waals that are weak.

2.    The procedure can be undone. It lacks specificity in nature.

3.    This procedure has several layers.

4.     Low enthalpy of adsorption (between 20 and 40 KJ/mole).

5.       Very little activation energy

6.       Desorption process simply occur.

7. Affecting variables include pressure, temperature, and the surface area of the adsorbent.

 (B) Adsorption or chemisorption of chemicals

It is caused by the potent chemical interactions of the adsorbent and adsorbate.

Characteristics:

1.  Strong chemical forces are the nature of the forces, and nature is quite particular.

2.      It cannot be reversed

3. It is a single-layered technique with high adsorption enthalpies (between 40 and 400 KJ/mole).

4.      Extremely high activation energy

5.     Desorption is very challenging

6.   Factors influencing depend on Adsorbent surface area and adsorbate type Temperature.

Pressure's impact on a gas's adsorption on a solid

The ratio of gas adsorbed to the total gas is proportional to the gas pressure. Adsorption increases with pressure until a maximum is reached and then remains constant.

Temperature effects on gas adsorption on solids

Gases always adsorb onto solids in an exothermic manner. Physical adsorption adheres to the Lechatlier Principle, which states that as temperature rises, less gas is adsorbed. As temperature rises, chemisorption increases. It reaches its peak before declining. Adsorption isobars are obtained by graphing the proportion of gas adsorbed and temperature at constant pressure.

Adsorption Isotherms

Isotherm means constant temperature, so at constant temperature amount of gas adsorbed on adsorbent with pressure expressed by using curve this is called adsorption isotherm.

Isotherm of Freundlich Adsorption

The quantity of gas a unit mass of solid adsorbent can adsorb and pressure at a specific temperature can be empirically related, according to German scientist Freundlich, in 1909.

                                     x/m = k.P^1/n (n > 1)

where, at pressure "P," "x" is the mass of the gas adsorbed on the mass "m" of the adsorbent. The constants "k" and "n" depend on the characteristics of the gas and the adsorbent at a specific temperature.

To illustrate the relationship, a graph representing the mass of the gas adsorbed per grams of the adsorbent is shown against pressure. Physical adsorption here reduces as temperature rises at a fixed pressure. When the pressure is high, the curves saturate. Taking the log of the above equation now,

                                  Log x/m = log k + 1/n log P.

We can plot log x/m on the y-axis and log P on the x-axis in order to examine the reliability of the Freundlich isotherm. The Freundlich isotherm is true if the plot displays a straight line; otherwise, it is false. The intercept on the y-axis provides the value of log k, whereas the slope of the straight line provides the value of 1/n.

Freundlich Adsorption Isotherm

Limitations

Value of 1/n ranges between o and 1 only so,

When x/m is constant and 1/n = 0, the adsorption is free of pressure dependence. The amount of adsorption is directly proportional to pressure when 1/n = 1, x/m = k P, or x/m P.

Results from experiments back up both of the conditions mentioned. The experimental isotherms appear to always approach saturation at high pressure. Freundlich isotherm fails at high pressure because it cannot account for this observation.

The adsorption of gases on solids under higher pressure is not covered by it.

Isotherm of Langmuir Adsorption

At greater pressures, the Freundlich adsorption isotherm fails, indicating that his theory is not totally accurate. Langmuir presented a novel idea in 1916 that takes into account the influence of chemical (intermolecular) interactions. The Langmuir adsorption isotherm is the mathematical equation he developed for the adsorption phenomena based on the kinetic molecular theory of gases.

 

θ = bP / (1 + bP)

where,

θ is of the surface covered by species that have been absorbed

The adsorption coefficient is b.

P is the pressure being used.

Assumptions

The Langmuir adsorption isotherm requires the following presumptions in order to function:

1.      The solid surface must be uniform.

2.      It ought to contain a set quantity of adsorbent surface.

3.      Only one molecule can adsorb at each location (mono-layered adsorption).

4.      A monomolecular layer is where molecules can only adsorb.

5.      In the vapour phase, the adsorbed gas acts perfectly.

6.      The molecules that are adsorbed do not interact.

7.      At their dynamic equilibrium, the rates of adsorption and desorption become equal.

Emulsions

Emulsions are liquid-based colloidal solutions that contain both the dispersed phase and the dispersion medium.

Paints, colours, milk, and vanishing cream, for instance. Surface chemistry divides emulsions into two categories based on the dispersion medium:

Water and Oil Emulsions

This involves dispersing oil or fat droplets in water. Consider milk.

Oil Emulsions with Water

The water droplets in this are mixed with the oil. For instance, vanishing cream.

Emulsions are prone to instability; hence emulsifiers are typically added to improve stability. Example: Casein is a natural emulsion found in milk.

Emulsion applications

They are utilised in syrups, Paints, Toothpaste, Fat Digestion, Colorants and dyes

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Colloidal chemistry, Colloids 

What is Colloidal chemistry, Colloids ?

Colloidal chemistry, Colloids

 

Colloids

 

 Here you will learn about introduction of colloids, their classification and preparation methods.

Introduction of Colloids:

In a solid, liquid, or gaseous media, one or more components are dispersed as relatively large solid particles or liquid droplets to form a mixture known as a colloidal mixture. A colloid's particles are frequently electrically charged, remain scattered, and do not settle as a result of gravity.

Any substance, including thin films and fibers, with at least one dimension in this general size range, which covers a range of around 10⁷ to 10³ cm, is referred to as a colloid. This term also refers to any substance that contains particles that are significantly larger than atoms or regular molecules yet too small to be visible to the unassisted eye.

Simply we say that colloids are heterogeneous solutions in which one substance is broken down into very small size particle and disperse into second substance thoroughly. Their particle size ranges between 1 to 1000nm. Colloids' dimension, which falls between atomic and bulk dimensions, is the cause of many of their intriguing characteristics.

Surface and Interface

The word "surface" is used to refer to a phase boundary in chemistry. A surface does not have thickness geometrically, only area. However, chemically, it is an area where the properties of one phase and the phase next to it differ. This transformation happens over at least molecular-scale distances. Therefore, for us, a surface has a thickness that, when we want a purely geometric description, we may envision it reducing to zero. In this context, the word interface is sometimes employed. This phrase just emphasizes that the surface of interest is the zone that separates two phases.

Difference between solution, suspension, and colloids 

Difference

Colloids classification

There are four types of colloids and they further subdivided into different types.

Sols and gels can be change into one another and these are reversible this phenomenon is called as thixotrpy.

(A) Based on physical state

1.Emulsions

These are solutions in which dispersion medium and dispersed phase are both liquid. These can be two types,

i) Oil in water

Oil is dispersed phase and water is dispersion medium. For example, milk.

ii) Water in oil

Water act as dispersed phase and oil act as dispersion medium. For example, vanishing cream.

2. Gels

Solid act as dispersion medium and liquid act as dispersed phase like butter.

3. Aerosols

Air is present as dispersion medium in these colloids. Examples include, dust , smoke and clouds.

4. Solid solutions

In these types of solution solid is used as dispersion medium and other substance act as dispersed phase, like gemstone. 

(B) Colloid classification based on affinities to the carrier fluid

Lyophilic and Lyophobic are the terminologies used to describe colloidal "particles" based on their affinity to the fluid in which they are disseminated. Literally, these words imply "solvent loving" and "solvent fearing," respectively. The phrases hydrophilic or hydrophobic are frequently used when referring to a medium or solvent made of water. However, when used to categorize colloids, the distinction is not always clear-cut. This nomenclature is especially helpful when assessing surface activity such as the wettability of a surface.

1.Lyophilic colloids

The term "lyophilic colloids" is typically used to describe soluble macromolecules with colloidal-sized individual particles (macromolecules like proteins or synthetic polymer chains). However, there are colloidal macromolecules with both lyophilic and lyophobic components (such as proteins with hydrophobic (hydrocarbon) portions and hydrophilic (peptide and carboxyl groups) portions).

 Micelles are a type of spontaneously forming small molecule cluster that forms in aqueous solutions (mostly) of specific compounds (therefore these are often called association colloids). Micelle production resembles phase separation because micellization begins at a specific concentration, known as the critical micelle concentration. The micelles, however, allow the distinct tiny molecules to maintain their individuality.

2.Lyophobic colloids

Lyophobic sols are irreversible, cannot recycle. There particles are visualized by using ultra microscope. For example, Metallic sols like Ag, gold etc.

(C) Dispersion medium-based classification

1.Acrosols

Dispersed medium is particles of air like smoke

2.Hydrosols

Water is present as dispersion medium in these colloids, like starch.

3.Alcosols

In these types of colloids alcohol is used as dispersion medium.

D) Sol Particles Based Classification

These are of two kinds,

1. Multi-molecular colloids

These colloids are formed by using Bredig^,s method like metallic sols(multi molecular sols). Their particles have van der walls forces. Their separation occurs easily and these are lyophobic unstable colloids.

2. Macromolecular colloids

As the name suggest their molecules are of big size, they are formed by demolition of macromolecular substances which convert into colloids size rang. Dispersed phase particles are polymers having large size. Naturally occurring macromolecules are enzymes, proteins etc. These are lyophobic colloids.

 

Colloidal solution preparation

Lyophilic sols are stable sols because of strong interaction forces among the medium and phase. There preparation occurs by using different methods.

(A) Condensation method

Condensation method, in this method solute particles of small size condense and form dispersion phase.

1.Chemical method

i) Oxidation

Colloids of Sulphur are obtained by this method, oxygen is passed into the solution of hydrogen sulphide by using an oxidizing agent, HNO₃, H₃Br₂ etc.

 2H₂S + O₂ → 2H₂O + 2S (Sulphur sol)

ii) Double Decomposition

Arsenic sulphide sol is prepared by using arsenic oxide cold solution and passing hydrogen sulphide gas through this solution in water.

AS₂O₃ + 3H₂S → AS₂S₃ + 3H₂O Arsenic sulphide (sol)

iii) Reduction

Pt, Au and silver metal colloids are formed by this method. Reducing agents like phenyl hydrazine, hydrogen peroxide, formaldehyde etc. are used. Metals are converted into aqueous solution of their salts than reacted with reducing agent.

Gold sols are called as purple of Cassius because these are prepared by the reduction of gold chloride solution that has purple color.

2AuCl₃ + 3SnCl₂ → 3SnCl₄ + 2Au (gold sol)

2AuCl₃ + 3HCHO + 3H₂O → 2Au + 3HCOOH + 6HCl

iv) Hydrolysis

Different types of salt solutions are hydrolyzed rapidly by boiling. As an example, aluminum hydroxide and ferric hydroxide are formed by this method as,

 FeCl₃ + 3H₂O → Fe(OH)₃ + 3HCl colloidal sol

If sodium silicate is hydrolyzed than silicic acid sols are formed.

v) Colling

Excesses Colling method, in this method colloidal sol of ice are formed. Ice act as organic solvent in this method like chloroform ether and sol of ice is formed by Colling the water solution an solvent till its freezing point. Water molecules separate in solution and combine together to form colloidal size particle.

vi) Changing physical state and solvent

If the solvent in which solutions are normally formed and the state in which solutions exist as stable is changed then their true structure is changed because the forces disturbed their molecules and solutions convert into colloidal solutions. For example, Mercury and Sulphur sols are formed by using cold water which contains stabilizer like ammonium salt is passed through mercury and Sulphur (physical state change).

Sulphur and phosphorus solution are soluble in alcohol but not soluble in water their sol can be formed by passing their alcoholic solution into water (solvent change). Milky solution formed.

(B) Dispersion Method

These techniques involve the breaking up of a substance's (suspension) big particles into smaller ones. The strategies listed below are used.

1.Mechanical dispersion

This technique involves first grinding the material into large particles. To create a suspension, it is next combined with a dispersion medium. A colloidal mill is then used to grind the suspension.

It comprises of two metallic color’s moving at an extremely fast 7000 revolutions per minute in the opposing direction, almost touching each other. The mill's dyes are spaced apart in such a way as to subject a coarse suspension to a strong shearing force, producing particles of colloidal size. This technique can be used to create a colloidal solution of black ink, color, lacquers, and colors.

2. Electrical Dispersion or Bredig’s Arc Method

The preparation of gold, copper, silver, or platinum sols is done using this technique. The metal that needs to be turned into a sol is fashioned into a two-electrode device and submerged in a dispersion medium like water or another liquid.

Ice is used to keep the dispersion medium chilly. The electrodes are connected by an electric arc. A colloidal solute is produced by and given great heat. For stability and cooling purposes, electrolytes are utilized in this procedure.

3. Peptization

Peptization is the process by which a freshly made precipitate is changed into a colloidal solution. In this method, the Peptization agent, also known as the peptizing agent, is added in smaller amounts along with the electrolyte.

 

See more , Surface chemistry

Zeolites, Catalysis, shape selective catalysis and prosperity 

Emulsions, Adsorption, Adsorption Isotherm