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Surface chemistry is concerned with the phenomena that take place at surface or the interface. The interface or the surface is represented by segregating the bulk phases with the use of a hyphen or a dash. For instance, the surface between gas and solid could be represented using gas/solid. Due to the complete incompatibility the gas and solid, there is no interfacial space between the gas and solid. The bulk phases are encountered in the field of surface chemistry could be pure solutions or compounds. The interfaces are typically couple of molecules in thickness, however its surface is dependent in the dimension of molecules of bulk phases. Numerous important phenomena, notable in particular are corrosion electrochemical process, heterogeneous catalysis dissolution and crystallization occur at the interfaces. The topic of surface chemical applications is a broad one, with many uses in industries, work and everyday life. Best JEE coaching in Dimapur.

To conduct surface research with precision is essential to have a perfectly smooth surface.¬†With a vacuum that is extremely high, on the range of 10-8-10-9 pascal, the possibility is there to get an super-clean surfaces of metals.¬†Solid materials with these clear surfaces must be kept in a vacuum or they’ll be covered with molecules of the principal components of air, specifically dioxygen, and diitrogen.¬†In this unit you will learn about the most important aspects of surface chemistry, such as catalysis, adsorption, and colloids such as emulsions, gels.¬†Surface ¬†There are numerous examplesthat show how the surface solids has the capacity to attract and keep those molecules from the substance with the substance it comes in contact.¬†The molecules are only present on the surface, and do not penetrate further in the middle.¬†The concentration of molecular species on the surface, rather than within all of the liquid or solid is referred to as the adsorption.

The molecular substance or species that is concentrated or forms on the surface, is referred to as adsorbate, and the substance on the surface of which the adsorption occurs is known as an the adsorbent.¬†Adsorption is fundamentally an effect of the surface.¬†Solids, especially in a states that are finely divided are characterized by their large surface which is why silica gel, charcoal, clay, alumina gel colloids, metallics in finely divided state and others.¬†serve as excellent absorbents.¬†Adsorption takes place (i) When gas such as O2 H2, CO, Cl2 or SO2 are placed in a closed vessel with charcoal that has been powdered, it is evident that the gas’s pressure inside the vessel is reduced.¬†The gas molecules are concentrated at its surface on the charcoal i.e. gas molecules are attracted to the surface.Best JEE coaching in Dimapur.¬†(ii) In the presence with an organic color, such as Methylene Blue, after the charcoal of animals is added, and the solution is shaken well and shaken, you can see that the filtrate becomes colorless.¬†

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The dye’s molecules are then deposited upon the surfaces of the charcoal i.e. they are absorbed.¬†(iii) Aqueous solutions of sugar that has been transported over animal charcoal, is colorless since the coloring substances are attracted by charcoal.¬†(iv) It is observed that the air is made dry when it comes in contact with silica gel as the water molecules become adsorbed onto surfaces of gel.¬†It is evident from these examples that solid surfaces are able to hold the molecules of liquid or gas through adsorbed properties.¬†The removal of the adsorbed substance from the surface where it has been attracted is referred to as desorption.¬†When adsorption occurs, substances are concentrated at the surface , and cannot penetrate through the surface into the majority of the adsorbent. In contrast, when it is absorption, the substance is evenly distributed across the entire solid.¬†Best JEE coaching in Dimapur.

For instance, if an untreated chalk stick is submerged in dye, the surface maintains the color of the ink because of the adsorption of colored molecules, while the solvent in the ink is absorbed deep into the sticks because of absorption.¬†When the chalk stick is broken it turns out to be white from the inside.¬†It is possible to distinguish in adsorption and absorption using the illustration from water vapour.¬†Water vapours are absorbed through anhydrous calcium chloride and then adsorbed with silica gel.¬†In the case of adsorption, it is the case that the concentration of the substance is increased only on the area of the adsorbent’s surface, when absorption is the case, the concentration is constant throughout the majority of the solid.¬†Both absorption and adsorption may occur simultaneously.¬†The term”sorption” is used to refer to both processes.¬†Adsorption occurs due to the nature of the particles on the surface of the adsorbent do not reside within the same environment as the particles within the bulk.¬†

In the adsorbent, all the forces that interact on the particle are interspersed. 5.1.1 Distinction between Absorption and absorption 5.1 The process of adsorption 5.1.2 Mechanisms that Adsorption operates 2015-16(20/01/2015) Surface Chemistry is balanced. However, on the surface , the particles are not enclosed by molecules or atoms that are of their own kind on all sides, which means they have unbalanced or even attracted forces.¬†The forces acting on the adsorbent play a role in attracting the adsorbate particles onto its surface.The degree of adsorption grows when the surface area per volume of the substance in a particular temperatures and pressure.¬†Another significant aspect that is associated with the process of adsorption is the heat generated by the adsorption.¬†In the course of adsorption, there’s always a reduction in residual forces on the surface, i.e. it is a less surface energy, which is reflected as heat.¬†Adsorption is usually an exothermic procedure.¬†That is, the H of adsorption is negative.¬†Best JEE coaching in Dimapur.

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When an element is adsorbed it’s freedom of movement of its molecules is limited.¬†This results in a decrease in the amount of entropy that the gas has after the adsorption process, i.e., S is negative.¬†Adsorption results in a the decrease in enthalpy, as well with a decrease in the entropy of the system.¬†In order for a process to be spontaneous, the thermodynamic condition is that, at a constant temp and pressure should have a negative value, i.e. that there must be a reduction in the Gibbs energy.¬†Based on equation, G = + TS, G could be negative if the H value is sufficient negative value, as – T is positive.¬†Therefore, in the adsorption process that is spontaneous, the mix of the two variables creates G negative.¬†As the process proceeds the H gets less and less negative until H is equal to TS and then G decreases to zero.¬†Best JEE coaching in Dimapur.The equilibrium state is achieved.¬†There are two kinds of adsorption of gas on solids.¬†If the accumulation in the form of gases on a solid happens because of van der Waals’ forces that are weak forces, then the adsorption process is known as physical adsorption, or physisorption.¬†

When gaz molecules, or the atoms have been firmly attached to the surface of the solid by chemical bonds, this is referred to as chemical adsorption or the chemisorption.¬†Chemical bonds could be ionic or covalent in the nature of things.¬†Chemisorption requires a significant amount of energy of activation and is hence, commonly called activated adsorption.¬†Both processes can occur at the same time, and it’s difficult to identify the nature of the adsorption.¬†Physical adsorption at a low temperatures could be transformed into chemical adsorption when the temperature is raised.¬†For example, dihydrogen is first adsorbed on nickel by van der Waals’ forces.¬†Hydrogen molecules then break apart into hydrogen atoms that are held onto the surface through chemical adsorption.¬†A few of the key characteristics of both kinds of adsorption can be found below the characteristics of the physisorption (i) Absence of specificity: The face of the adsorbent will not exhibit any preference for one particular gas, since van der Waals forces can be applied to any surface.¬†(ii) The nature of the adsorbate:

The quantity of gas that is adsorbed by a material is contingent upon the nature of the gas.¬†In general, readily gasses that are liquefiable (i.e. having higher temperatures at critical) are easily absorbed since Van der Waals’ force is more powerful at temperatures near critical.¬†For example, 1 gram of activated charcoal absorbs more sulfur dioxide (critical temperature 630K) and methane (critical temperature of 190K) that is still greater than 4.5 milliliters of dihydrogen (critical temperature 33K).¬†5.1.3 The types of adsorption 2015-16(20/01/2015) Chemistry 124 (iii) Reversible nature: The physical adsorption of gases by solids is usually reverse-able.¬†So, the Solid + Gas + Gas + Heat Gas is more readily adsorbed in the event that pressure increases, the volume of gas shrinks (Le-Chateliers’s theory) The gas is able to be eliminated by reducing pressure.¬†Because the process of adsorption is exothermic, physical adsorption is readily attainable at low temperatures, and it decreases as temperatures rise (Le-Chatelier’s theory).¬†(iv) Area of the the adsorbent.¬†Best JEE coaching in Dimapur.

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The amount of adsorption is increased when the its surface.¬†Therefore, metals that are finely divided and porous substances with huge surface areas are great for adsorbents.¬†(v) Adsorption’s enthalpy Physical adsorption is an exothermic reaction however the enthalpy associated with the process is very low (20to 40 kJ mol-1).¬†This is due to the fact that it is a result of the strong attraction that exists between molecules in gas and the surface is only due the weak van der Waals’ forces.¬†The characteristics of chemisorption (i) High specificity Chemisorption is very specific, and will only occur when there is the possibility of a chemical bond between the adsorbent as well as the adsorbate.¬†For instance, oxygen is attracted to metals because of oxide formation , and hydrogen is absorbed by transition metals because of the formation of hydrides.¬†(ii) Reversibility: Since Chemisorption is a process that involves the formation of compounds It is typically unreversible in the natural environment.¬†Best JEE coaching in Dimapur.

Chemisorption is an exothermic procedure, but the process is slow at low temperatures , on due to the high energy involved in activation.¬†Similar to most chemical changes the rate of adsorption increases when temperatures increase.¬†The physisorption of gas that is adsorbed at low temperatures may transform into chemisorption at high temperature.¬†The majority of the time, high pressure is favorable for the chemisorption.¬†(iii) Area of the surface: Similar to physical adsorption too, chemisorption grows with the increase in area of the absorbent.¬†(iv) Adsorption enthalpy Chemisorption has an enthalpy that is extremely high (80-240 kJ/mol ) due to the chemical bonding.¬†1.¬†It arises because of van der Waals’ forces.¬†2.¬†It’s not unique in nature.¬†3.¬†It is natural to be reversible.¬†4.¬†It is based on the nature of gas.¬†The gas that is more easily liquefiable are quickly absorbed.¬†5.¬†Adsorption’s enthalpy is very minimal (20-40 kJmol-1 )in this scenario.¬†1.¬†It’s due to the formation of chemical bonds.¬†2.¬†It is very unique in the nature of things.¬†3.¬†It’s irreversible.¬†4.¬†It is also dependent on the type of gas.¬†

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Gases that interact with the substance display the chemisorption.¬†5.¬†The enthalpy of adsorption can be high (80-240 kJ mo-1) in this instance.¬†Table 5.1 Comparative Analysis of Physisorption and Chemisorption Chemisorption 2015-16(20/01/2015) 135 Surface Chemistry The variance in the amount of gas that is absorbed by the adsorbent at a constant pressure can be represented by an equation known as an adsorption isotherm.¬†Freundlich isotherm of adsorption: Freundlich in 1909 provided an empirical correlation between the amount of gas that is absorbed by the an adsorbent of a unit mass and the pressure that is maintained at a certain temperature.¬†The relation can be expressed using the following equation: M = k.p 1. (n + 1.) … (5.1) in which x is the weight of gas that is adsorbed onto mass of the adsorbent. pressure P. K and n have constants, and depend on the characteristics of the adsorbent as well as the gas in a certain temperature.¬†The equation is typically expressed as an equation where the mass of gas that is absorbed per kilogram of the adsorbent is plotted against the pressure.¬†Best JEE coaching in Dimapur.

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These curves suggest that at a certain pressure there is a reduction in physical adsorption as a result of an increasing temperature.¬†The curves are always able to reach saturation at higher pressure.¬†Logarithms of equation.¬†(5.1) Log x M = log k + 1 log p … (5.2) The accuracy of the Freundlich isotherm is verified by plotting log x M on the y-axis (ordinate) as well as log p along the the x-axis (abscissa).¬†If it appears to be straight, then that means the Freundlich isotherm is true and not otherwise (Fig.¬†5.2).¬†Straight line slope provides the value 1 n .¬†The y-axis intercept yields the value of one logarithm. Freundlich isotherm explains the behavior of adsorption in a general way.¬†The number 1 n may be a value between 1 and 0 (probable range of 0.1 up to 0.5).¬†So equation (5.2) is valid over the pressure range.¬†5.1.4 Adsorption Isotherms Figure.¬†5.2: Freundlich isotherm 6.¬†The low temperature can be beneficial for Adsorption.¬†Best JEE coaching in Dimapur.¬†The adsorption rate decreases as you increase temperature.¬†7.¬†A minimal amount of activation energy is required.

It is dependent on the area of the surface. It grows with the increase in the surface area. 9. It forms multimolecular layer on the surface of the adsorbent under pressure high. 6. The high temperature is favorable for the adsorption process. The adsorption rate increases with the rise of temperature. 7. Sometimes, high activation energy is required. 8. It is also dependent on size of the surface. It also increases as the surface area. 9. It is a result of unimolecular layers. 195 K 244 K 273 K x m p Fig. 5.1 The Adsorption Isotherm 2015-16(20/01/2015) Chemistry 126 When1 1 = 0 and x m is equal to constant. The adsorption becomes dependent on pressure. When 1 n = the x m value is k the p i.e. x M p, the amount of Adsorption is directly affected by pressure. Both conditions are confirmed by experiments. The experimental isotherms are always seen to reach saturation when pressure is high. This cannot be explained with Freundlich isotherm. Therefore, it fails at high pressure. Solids are able to adsorb solvents from solutions as well. 

When a solution containing Acetic acid within water shakes using charcoal, a small portion that is acidic gets taken up by the charcoal, and the acid’s concentration diminishes within the solution.¬†The litmus solution, too, when shaken with charcoal turns colorless.¬†Its precipitate of Mg(OH)2 develops a blue hue when precipitated with magneson reagent.¬†The color is caused by the adsorption of magneson.¬†The following observations were observed in the context of adsorption occurring in the solutions: (i) Adsorption is less with increasing temperature.¬†(ii) The degree of adsorption grows by increasing the size of the surface that is adsorbent.¬†(iii) The amount of adsorption is dependent on the amount of solute in the solution.¬†(iv) The amount of adsorption is dependent on the characteristics of the adsorbent as well as the adsorbate.¬†The exact mechanism for the process of adsorption in solution is not yet understood.¬†Best JEE coaching in Dimapur.¬†The equation of Freundlich roughly describes the behavior of adsorption in solution, but with the exception that rather than pressure is taken into account, the concentration of solution considered, i.e., x M = kC 1/n …(5.3) (C C is the equilibrium value, i.e., when the adsorption process is completed).¬†

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If we calculate the logarithm in the equation above and calculating log x M = logk + 1 logC = n …(5.4) By plotting log x m and log C, a straight line is created that proves the accuracy for Freundlich isotherm.¬†It can be verified in a laboratory setting by using solutions of various concentrations of acetic acids.¬†Equal amounts of solution are added in equal quantities of charcoal in various flasks.¬†It is calculated within each flask, following the adsorption process.¬†The difference between the final and initial concentrations determine what is known as x.¬†With the equation above the the validity of Freundlich isotherm can be proved.¬†Adsorption is a phenomenon that has numerous applications.¬†Some of the most significant ones are as follows: (i) Production of high vacuum: The rest of the traces of air could be absorbed by charcoal in vessels that are evacuated by the vacuum pump, resulting in an extremely high vacuum.¬†Best JEE coaching in Dimapur.¬†The applications for Adsorption 2015-(ii) Masks for gas: A gas mask (a device that is made up of activated charcoal, or a mix of adsorbers) is typically used to breathe in coal mines in order to adsorb toxic gases.¬†

(iii) control of the humidity level: Silica as well as aluminum gels are utilized as adsorbents in removing humidity and removing moisture. (iv) Elimination of color-producing matter in solutions. Animal charcoal eliminates the colours of solutions by adsorbing colored impurities. (v) Heterogeneous catalysis The adsorption of the reactants onto the surface of the catalysts boosts the speed of reaction. There are many gaseous reactions with industrial significance that require solid catalysts. Manufacturing of ammonia with iron as catalyst, manufacturing of H2SO4 using a contact process , and using nickel finely divided in the hydrogenation process of oils are fantastic instances for heterogeneous catalysis. (vi) Removal of the inert gasses: Due to the different the degree of adsorption of gases through charcoal, a mix of noble gases may be separated using adsorption of coconut charcoal at various temperatures. (vii) Curing illnesses: A variety of medications are utilized to eliminate germs, by being coated with the particles. 

(viii) Froth floating process Low grade sulfur ore is concentrated by segregating it from silica as well as other earthy material by using Pine oil, and then frothing agents (see Section 6). (ix) Indicates adsorption: The surfaces of certain precipitates , such as silver halides, possess the ability of adsorbing dyes such as fluorescein, eosin, etc. and thus resulting in a distinctive color at the end of the spectrum. (x) Chomatographic analysis that is based on the adsorption phenomenon can be used for a variety of purposes within industrial and analytical fields. In-text Questions 5.1 Give two distinct features of Chemisorption. 5.2 What causes physisorption to decrease when temperature increases? 5.3 What makes powdered substances more effective as adsorbents than crystallized counterparts? When heated, potassium chlorate quickly, rapidly decomposes to give dioxygen. Best JEE coaching in Dimapur.

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Decomposition takes place within the range of 653-873K.¬†2KClO3 – 2KCl + 2O2 But, when a tiny amount Manganese dioxide gets added the process of decomposition occurs in a much lower temperature, i.e., 473-633K and at an faster rate.¬†Manganese dioxide that is added remains the same in terms of its weight and composition.¬†Similar to this it is possible for the rates of several chemical reactions can be affected due to the presence of a foreign chemical.¬†5.2 Catalysis 2015-16(20/01/2015) Chemistry 128 The study of the effects of various chemicals on rate in chemical reaction was initially done by Berzelius in 1835.¬†He proposed the term catalyst for these substances.¬†Substances that increase the speed of chemical reactions and themselves remain chemically and quantifiably unaltered after the reaction are called catalysts and the process is also known as catalysis.¬†You’ve already learned about the role of catalysts at Section 4.5.¬†Best JEE coaching in Dimapur.

Promoters and poisons substances that boost the performance of catalysts, while poisons reduce the effectiveness of catalysts.¬†For instance, in Haber’s method for the production of ammonia, molybdenum functions as an inducer for iron that can be utilized as catalyst.¬†(g) + 3H2 (g) + 3H2 (g) Fe(s) Mo(s) 2NH3 (g) Catalysis is broadly classified into two categories: (a) Homogeneous catalysis In the event that the reactants and catalyst are within one phase (i.e. gas or liquid) the procedure is termed homogeneous catalysis.¬†Here are some of instances of homogeneous catalysis (i) Oxidation of sulfur dioxide into sulphur trioxide by dioxygen when there are nitrogen oxides as catalysts within the lead chamber procedure.¬†2SO2 (g) + O2 (g) NO(g) 2SO3 (g) The reactants, sulphur dioxide, and oxygen, as well as the catalyst, nitrogen dioxide, are all part of one phase.¬†(ii) The hydrolysis of methyl acetate occurs through H+ ions provided with hydrochloric acids.¬†CH3COOCH3 (l) + H2O(l) HCI(l) CH3COOH(aq) + CH3OH(aq)¬†

The reactants and catalysts are present in identical phases.¬†(iii) The sugar hydrolysis is catalyzed by the H+ ions supplied by sulfuric acid.¬†(l) HSO (l) 2 4 C H O (aq) + C H O (aq) 6 12 6 6 12 6 Glucose fructose Solutions C H O (aq) + H O(l) 12 22 11 2 Solution Both the reactants as well as the catalyst are located in one phase.¬†(b) heterogeneous catalysis catalyst in which the catalyst and reactants are located in different phase is known as heterogeneous catalysis.¬†A few examples of heterogeneous catalysis can be found as follows: (i) Oxidation of sulfur dioxide into trioxide sulphur when while surrounded by Pt.¬†Pt(s) 2SO (g) 2SO (g) 2 3 The reaction is in a gaseous form while catalytic activity is solid state.¬†5.2.1 Homogeneous and heterogeneous catalysis 2015-16(20/01/2015) (20/01/2015) (ii) Combination of dihydrogen and dinitrogen to create ammonia in the presence iron that is finely divided in the Haber’s method.¬†Fe(s) 2NH (g) N (g) + 3H (g) 2 2 3 The reaction products are in a gaseous state, as the catalyst moves into solid state.¬†(iii) The oxidation process of ammonia into nitric dioxide with the help of platinum gauze as part of Ostwald’s procedure.¬†Best JEE coaching in Dimapur.

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Pt(s) 4NO(g) + 6H O(g) 4NH (g) + 5O (g) 3 2 The reaction products are in a gaseous condition and the catalyst in solid state.¬†(iv) The hydrogenation process of vegetable oils with the help of the finely separated nickel catalyst.¬†Ni(s) vegetables oils(l) + H (g) Vegetable ghee(s) 2. One of the reactants is in a liquid state, the other in gaseous state , while the catalyst remains in solid state.¬†This theory describes the mechanism behind heterogeneous catalysis.¬†The previous theory, also known as the adsorption theory of catalysis, claimed that reactants that are in gaseous states or in solution, are absorbed by their surfaces on the catalyst.¬†The increased concentration of the reactants on the catalyst’s surface enhances speed of the reaction.¬†Adsorption is an exothermic procedure and the heat generated by the process is used to boost the rate of reaction.¬†The catalytic reaction is explained by the concept that of an intermediate compound formationprocess, the theory he current adsorption theory is the amalgamation of the theory of intermediate compound formation and the traditional theory of adsorption.¬†Best JEE coaching in Dimapur.

The catalytic action is concentrated to the surfaces of catalysts. The mechanism is comprised of the following steps (i) The diffusion of reaction substances onto the surfaces on the catalyst. (ii) the adsorption of molecules of the reactant onto the surfaces of the catalyst. (iii) The occurrence of chemical reaction on the surface of the catalyst by the creation the intermediate (Fig. 5.3). (iv) The desorption of the reaction products off the surface of the catalyst and this makes the surface accessible for further reaction to occur. (v) diffusion of reaction products away the surface of the catalyst. The surface of the catalyst, in contrast to the interior of the bulk has liberated valencies, which serve as the place for the forces that attract chemically. In the event that a gas is into contact with a surface, its molecules will be stuck there by an unintentional chemical mix. If various molecules are absorbed together in a reaction, they could react, and result in the creation in the formation of brand new molecules. 

The resulting molecules could disappear leaving the surface for the newly formed reactants.¬†This theory is the reason why the catalyst remains the same in terms of chemical composition and mass after the reaction, and it is efficient 5.2.2 the Adsorption theory of Heterogeneous catalysis 2015-16(20/01/2015) Chemistry 130, even in tiny quantities.¬†However, it does not explain the actions of catalytic promoters or catalytic poisons.¬†The most important characteristics of solid catalysts (a) activity The performance of a catalyst is dependent on the power of chemisorption to a great extent.¬†Reactants need to be fairly strongly absorbed by the catalyst to activate.¬†But, they should not be so heavily adsorbed that they become immobilized and leave other reactants with no room on the catalyst’s surface to allow adsorbing.¬†It was discovered that in the hydrogenation reaction the catalytic capacity increases from groups 5 to 11 metals , with the highest activity as shown by the groups 7-9 from the periodic.¬†Best JEE coaching in Dimapur.

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O(l) 2H Pt O(l) 2H (g) + O (g) 2 2 (b) Its selectivity characteristic of a catalyst’s selectivity is the ability of a catalyst to direct a process to yield a specific product at the same time, under similar conditions of the reaction, many different types of products are achievable.¬†The specificity of different catalysts with the similar reactants can differ.¬†For instance, starting with CO and H2 and using various catalysts, we can get different products.¬†Therefore, it is concluded that the activity of a catalyst is extremely selective in the natural world.¬†Therefore, a chemical that acts as a catalyst for one reaction might not be able to catalyze a different reaction.¬†The catalytic reaction which is dependent on the structure of the pores of the catalyst as well as how large the reactant and the product molecules is referred to as shape-selective catalysis.¬†Zeolites are great catalysts that are shape-selective due to their honeycomb-like structures.Best JEE coaching in Dimapur.

Aluminosilicates with a three-dimensional web of silicates wherein some silicon molecules are substituted aluminum atoms, resulting in Al-O-Si framework. The reactions occurring in zeolites depend on the shape and size of the reactant and product molecules, and also on their pores as well as the cavity within the Zeolites. They can be found in nature and synthesised to provide catalytic specificity. Zeolites are extensively employed as catalysts in industry of petrochemicals for cracking hydrocarbons as well as isomerisation. One of the most important catalysts used by zeolites in the oil manufacturing industry is called ZSM-5. ZSM-5 converts alcohols to gasoline (petrol) by dehydrating them and resulting in an encapsulation of hydrocarbons. Enzymes are complex organic nitrogenous compounds that are created by living animals and plants. They are protein molecules with a high molecular mass. They create colloidal solutions in water. 

They’re extremely efficient catalysts that catalyze a variety of reactions, particularly those that are associated to natural processes.¬†Many of the reactions that take place within the body of animals and plants in order to sustain the cycle of life are catalyzed by enzymes.¬†They are, therefore called biochemical catalysts. The process is called biochemical catalysis.¬†Numerous enzymes have been isolated in crystallized form by living cell.¬†The first enzyme was synthesized in the lab in 1969.¬†Here are the examples of reactions that are catalyzed by enzymes: (i) Inversion of cane sugar: The enzyme invertase converts sugar from cane into fructose and glucose.¬†(ii) conversion of glucose to ethyl alcohol The enzyme zymase turns glucose into ethyl Alcohol, and carbon dioxide.¬†Zymase 2C OH(aq) + 2CO (g) C H O (aq) 6 12 6 2 5 2 Glucose Etyl alcohol (iii) Conversion of maltose into starch: Diastase enzyme converts starch to maltose.¬†Diastase, nC H O (aq) 2(C H O ) (aq) + nH O(l) 6 10 5 n 2 12-22 11 Starch Maltose (iv) Conversion of maltose to glucose.¬†Best JEE coaching in Dimapur.

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Maltase enzyme converts maltose to glucose.¬†Maltase 2C H O (aq) C H O (aq) + H O(l) 12 22 11 2 6 12 6 Maltose Glucose (v) The decomposition of urea into ammonia as well as carbon dioxide: Urease’s enzyme is responsible for this decomposition.¬†Urease 2NH (g) + CO (g) H O CONH (aq) + O(l) 2 2 O(l) 2 2 2 3 (vi) In the stomach the pepsin enzyme transforms proteins into peptides. Meanwhile, in the our intestines, the pancreatic trypsin transforms proteins into amino acids via hydrolysis.¬†(vii) Transformation of milk into curd It is an enzymatic process that is caused by the lactobacilli enzymes found in curd.¬†5.2.4 Enzyme catalysis 2015-16(20/01/2015) Chemistry Characteristics of enzyme catalysis The catalytic process of enzymes is distinctive in its effectiveness and its high level of specificity.¬†The following features are shown through enzyme catalysts (i) The most efficient A single enzyme molecule can transform millions of molecules of the reactant in a minute.¬†Best JEE coaching in Dimapur.

(ii) Very specific Each enzyme is specialized to a particular process, i.e. the catalyst is unable to catalyze more than one reaction.¬†For instance the enzyme urease is responsible for an urea-hydrolysis alone.¬†It doesn’t catalyze hydrolysis of other amides.¬†(iii) Extremely active at optimal temperature: The speed that an enzyme reacts is maximum at a specific temperature, also known as the optimal temperature.¬†Between the two sides of the ideal temperature, enzyme activity declines.¬†The optimal temperature range for enzyme activity is 298 to 310K.¬†The body temperature of the human being is at 310K is suitable to enzyme-catalyzed reactions.¬†(iv) Extremely active in optimal pH A: The speed of an enzyme-catalysed process is the highest at a certain pH known as optimum pH which lies between pH values 7 and.¬†(v) Increased activity when activators and co-enzymes. enzyme’s activity increases in the presence of specific substances, also known as co-enzymes.¬†

It has been discovered that when a tiny non-protein (vitamin) is found in conjunction together with an enzyme its catalytic activity is significantly increased. Activators are typically metal ions, such as Na+, Mn2+ Cu2+, Co2+, etc. These metal ions, once weakly bound on enzyme molecules boost their catalytic capacity. Amylase when in contact with sodium chloride i.e., Na+ is catalytically extremely active. (vi) Effects of poisons and inhibitors: Similar to other catalysts, enzymes can also be blocked or poisoned due to the presence of specific substances. The inhibitors or poisons work with the functional groups active on the surface of enzymes and can reduce or remove the catalytic activities that the enzymes perform. The usage of many medications is a result of their function as inhibitors of enzymes within the body. Mechanisms of catalytic enzymes There are numerous cavities that are found in the colloidal surface from enzymes. They are of a distinctive form and have active groups, such as COOH, -NH2, -SH or -OH. Best JEE coaching in Dimapur.

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These are an active table 5.2 The Enzymatic Reactions Source Enzymatic reaction Invertase Yeast Sucrose Zymase Yeast with fructose and Glucose glucose РEthyl alcohol as well carbon dioxide diastase malt starch Maltose Maltase Yeast РРGlucose Urease Soyabean Urea Ammonia and Carbon dioxide Pepsin Stomach proteins РAcids amino acids Table 5.2 provides a summary of several important reactions that occur in enzymatic processes. 2015-16(20/01/2015) The surface of 133 Chemistry is a process that occurs in the surfaces of the enzyme particles. These molecules, which are part of the reaction (substrate) with a identical shapes, can be inserted into these spaces just as keys fit into the lock. Due to that there are active molecules an activated compound is formed that then breaks down and yields the product. Therefore, enzyme-catalyzed reactions could be said to be carried out in two steps. Step 1 Binding of enzyme to substrate, resulting in the activated compound. Best JEE coaching in Dimapur.

E+S – 2. Decomposition of activated complex to create the product.¬†E + P A few of the key technical catalytic processes are described in Table 5.3 to provide an understanding about the value of catalysts in industrial processes.¬†5.2.5 Catalysts for Industry Process Catalyst Finely divided molybdenum promoter conditions that include 200 bar pressure as well as 723-773K temperature.¬†Today, a mixture of potassium oxide, and alumina is employed.¬†Platinised asbestos with a temperature of 573K.¬†The asbestos that is platinised or Vanadium Pentoxide (V2O5) Temperature 673-723K.¬†1.¬†Haber’s process for the manufacturing from ammoniaN2 (g) + 3H2 (g) 2NH3 (g) 2.¬†Ostwald’s method of manufacturing of the nitric acid.¬†4NH3(g) + 5O2(g) – 4NO(g) + 6H2O(g) 2NO(g) + O2 (g) – 2NO2 (g) 4NO2(g) + 2H2O(l) + O2(g) – 4HNO3(aq) 3.¬†Contact process for the production of sulfuric acid.¬†2SO2 (g) + O2 (g) 2SO3 (g) SO3(g) + H2SO4(aq) (aq) – H2S2O7(l) Oleum H2S2O7(l) + H2O(l) + H2O(l) 2H2SO4(aq)¬†

In Haber’s process hydrogen is created by the reaction of methane in the presence of NiO catalyst.¬†This process is known by the name steam reforming.¬†Why is it important to eliminate CO when ammonia is produced through Haber’s method?¬†5.5 Why is ester hydrolysis slow at the beginning, but it speeds up after a certain period of time?¬†5.6 How can we determine the function of desorption in catalysis.¬†The enzyme (catalyst) Substrate (reactants) Complex of enzyme-substrate Product of Enzyme E and S E – E + P E Active site S P P Figure.¬†5.4 Mechanism of the enzyme catalyzed reactions 2015-16(20/01/2015) Chemistry 134 We’ve learned during Unit 2 how solutions are homogeneous.¬†We also are aware that water containing sand when stirred produces the appearance of a suspension that slowly gets settled over time.¬†Between the extremes of solutions and suspensions we can find a huge range of systems known as colloidal dispersions, or colloids.¬†A colloidal is an heterogeneous system where the substance being dispersed (dispersed phase) in very small particles within another substance, referred to as dispersion medium.¬†Best JEE coaching in Dimapur.

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The main difference between a solution as well as the colloid is the size of the particle. In a solution the particles that compose it are small molecules or ions In a collloid, the dispersed phase could consist of particles from one macromolecule (such as synthetic polymer or protein) or an accumulation of many atoms molecules or ions. Colloidal particles are more massive than simple molecules, yet tiny enough to be suspended. Their diameter ranges from 1 to 1000 nanometers (10-9 to 10-6 meters). Colloidal particles possess a huge surface area per mass due to their tiny dimensions. Imagine a cube that has 1 cm sides. It covers an overall area of 6cm2 . If it was divided evenly into 1012 cubic cubes they are the size of colloidal particles that are large and possess a surface area of 60,000 square centimeters (or 6 sq m) . The huge surface area contributes to the unique properties of colloids that will be addressed in the next Unit. Best JEE coaching in Dimapur.

Colloids are classified according to on the basis of guidelines: (i) Physical state of dispersed and the dispersion medium (ii) Nature of the interaction between dispersed medium and dispersed phase (iii) The type of particles in the dispersed phase. Based on whether the dispersed phase or the dispersion medium are solidsor gases or liquids Eight types of colloidal systems could be created. A gas that is mixed with another gas creates a homogeneous mix which is not an actual colloidal system. Examples of the different kinds of colloids and their names typical of them are provided in Table 5.4. 5.4 classification of colloids of Colloids Dispersed Phase Solid Liquid Liquid Gas Medium for Gas Dispersion Solid Liquid gas Solid Gas Solid Liquid Type of colloids Solid Sol Sol Aerosol Gel Emulsion Aerosol Solid sol Examples of colored gem stones and glasses Paints Cell fluids Smoke dust butter, jellies, butter Fog from hair cream, mist clouds, sprays of insecticides, pumice stone Foam rubber Froth soap lather, whipped cream. 

Classification based on the Physical State of the Dispersed dispersion medium and Phase 2015-16(20/01/2015) 135 Chemical Surfaces A lot of well-known commercial items and nature objects can be classified as colloids.¬†For instance, whipped milk is a kind of foam, which is a gas that has been dispersed into liquid.¬†Foams for fighting fires that are used in emergencies at airport landings, are colloidal systems.¬†Most biological fluids are water-based sols (solids that are dispersed within water).¬†Within the typical cell, nucleic acids and proteins are colloidal particles that have been dispersed in an aqueous mixture of small molecules and ions.¬†From the many types of colloids described in Table 5.4 The most popular include sols (solids in liquids) and gels (liquids in solids) and Emulsions (liquids within liquids).¬†Best JEE coaching in Dimapur.¬†In this Unit we will pick on the discussion of’sols and emulsions.¬†In addition, it should be noted that if a liquid dispersion medium is water and the sol is referred to as hydrosol or aquasol. If you are using alcohol as the medium for dispersion, it’s known as alcosol, and the list goes on.¬†

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Based on the nature of the interaction between the dispersed and the media for dispersion, colloidal sols can be classified into two groups which are namely, the lyophilic (solvent attraction) as well as hydrophobic (solvent repelling).¬†When water serves as the medium used to disperse and the term used is both hydrophilic and hydrophobic.¬†(i) Lyophilic colloids The term ‘lyophilic’ refers to liquid-loving.¬†Colloidal sols that are directly created by mixing different substances, such as gelatine, gum, starch rubber. and the right liquid (the dispersion medium) are known as Lyophilic sols.¬†The most notable characteristic of sols like this is that they can be reconstituted if the dispersion media is separate from the dispersed portion (say through evaporate) sols can be reconstituted by mixing using the dispersion medium.¬†That’s why these sols are often referred to as reversible sols.¬†Top¬†JEE coaching in Dimapur.

Additionally, they are very stable and can’t be easily coagulated, as we will discuss in the future.¬†(ii) Colloids with lyophobic properties The word “lyophobic” means liquid-hating.¬†Substances that resemble the metals and their sulfuric compounds and so on. If they are mixed with dispersion medium, do not create an emulsified sol.¬†Colloidal sols of these substances can only be made using specific methods (as described in the next section).¬†Sols like this are known as lyophobic sols.¬†They are easily precipitated (or formed into coagulation) by the addition of small quantities of electrolytes by shaking or heating and are therefore not stable.¬†Furthermore, once they have been precipitated, they cannot provide the colloidal sol with a simple addition of dispersion medium.¬†Therefore, they are also known as irreversible sols.¬†Sols that are lyophobic require stabilising agents to help preserve their properties.¬†According to the nature of the particles that make up their dispersed phases, colloids can be classified as multimolecular macromolecular, and colloids with a connection.¬†(i) Colloids with multimolecular structure¬†

When dissolving, a huge number of atoms or compounds of an element assemble together to form species that have dimensions in the range of colloidal (1-1000 millimeters). The species produced are known as multimolecular colloids. For instance, a gold sol could contain particles of different dimensions with a large number of atoms. Sulphur sol comprises particles that contain thousands or more S8 sulfur molecules. 5.4.2 Classification based on the The nature of the interaction between Dispersed Phase and the Dispersion Media 5.4.3 Classification based on type of particles of the Dispersed Phase Multimolecular, Macromolecular and Related Colloids 2015-16(20/01/2015) Chemistry 136 (ii) Macromolecular colloids Macromolecular colloids (Unit 15) in the right solvents form solutions where the size of macromolecules can be within the range of colloidal. Top JEE coaching in Dimapur.

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These systems are referred to as macromolecular colloids.¬†These colloids are very robust and look like real solutions in many ways.¬†Examples of macromolecules that naturally occur include starch, cellulose as well as enzymes and proteins as well as those made by humans. include nylon, polythene, synthetic rubber, polystyrene and so on.¬†(iii) Colloids with a common chemistry (Micelles) They are certain substances that in small amounts act as normal strong electrolytes however, at higher concentrations they show colloidal behavior because of an accumulation of particles.¬†The aggregated particles that result are referred to as micelles.¬†They are also known as colloids that are associated.¬†Micelles form when they take place only at a certain temperature, known as”kraft temperature (Tk) and above a specific concentration known as the critical micelle concentration (CMC).¬†After dilution, the colloids transform back into individual micelles.¬†Top¬†JEE coaching in Dimapur.

Surface active agents like the synthetic and soaps are part of this category.¬†For soaps there is a CMC is between 10-4 and 10-3 mol L-1.¬†They contain both lyophilic and lyophobic parts.¬†Micelles can contain as many than 100 molecules.¬†The mechanism behind micelle formation Let’s take the case that soap products contain.¬†Soap is either sodium or potassium salt from a higher fat acid, which can be identified by the name RCOO-Na+ (e.g. sodium stearate, CH3 (CH2 )16COO-Na+, which is the main ingredient in numerous bars of soaps).¬†When it is dissolved in water it splits into RCOO+ and Na+ ions.¬†The RCOO- ions however, comprise two components: the long chain of hydrocarbons R (also known as a”non-polar tail”) that has a Hydrophobic (water repelling) and the polar group COO (also known as a polar-ionic head) that is hydrophilic (water affectionate).

Hydrophilic and hydrophobic components of the stearate ion.¬†¬†(a) Grease on the cloth (b) Stearate ions that are arranged in the vicinity of the grease droplet, and (c) Droplet of grease is surrounded by the stearate particles (micelle made) (a) (b) (c) (c) RCOO- ions are consequently, on the surface. They have their COO- groups present in water and the chains of hydrocarbons R remaining away from it, and remaining at the surface.¬†However, at a critical micelle concentration the anions are dragged into the majority of the solution, and then aggregate to form a spherical shape , with their hydrocarbon chains facing towards the center of the sphere. the COO- portion remaining onto the surface that makes up the sphere.¬†The resulting aggregate is called an ionic micelle’.¬†Top¬†JEE coaching in Dimapur.¬†The micelles could contain more than 100 Ions.¬†In the case of the detergents e.g. salt laurylsulphate CH3 (CH2 )11SO4 Na+ the pole group is -SO4 together with the long chain of hydrocarbons.¬†Therefore, the mechanism for micelle formation in this case is the same as for soaps.¬†

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The cleansing action of soaps has been said earlier that micelles are made up of an hydrophobic hydrocarbon with a similar the central core. The cleansing power of soap is because soap molecules form micelles around the droplet of oil in an arrangement that the hydrophobic portion of the stearate ions are in the oil droplet while the their hydrophilic component emerges from the grease droplet, similar to bristles (Fig. 5.7). Because the polar groups react with water and the droplet of oil that is surrounded by stearate ions are being pulled into water and then removed from the dirt surface. So soap aids in emulsifying and washing away fats and oils. This negatively charged layer surrounding the globules stops them from colliding and creating aggregates. Some of the most effective methods to prepare colloids are: (a) Chemical methods Colloidal dispersions are made through chemical reactions that result in the formation of molecules through two decompositions, an oxidation reduction, or hydrolysis. Top JEE coaching in Dimapur.

These molecules will then aggregate and lead to the formation of sols.¬†As2O3 + 3H2S- Double decomposition as2S3 (sol) + 3H2OSO2 +2H2S – The process of oxidation 3S(sol) + 2H2O 2 AuCl3 + HCHO + 3H2O – reduction 2Au(sol) + 3HCOOH FeCl3 + 3H2O hydrolysis Fe(OH)3 (sol) and 3HCl (b) Electrochemical disintegration or Bredig’s arc method This procedure is characterized by dispersion and condensation.¬†Colloidal sols made of metals like silver, gold platinum. They can be made by Stearate ion water¬† ¬†(b) Ionic micelle Figure.¬†5.6: (a) Arrangement of stearate-containing ions on the surface of water with low levels of soap. (b) arrangement of stearate-containing ions within the majority of water (ionic micelle) at the critical micelle concentrations of soap. 5.4.4 The preparation of colloids 2015-16(20/01/2015) Chemistry 138 5.10: Electro-dialysis medium.¬†5.10 Electro-dialysis medium Ice bath 5.10: Medium Ice-bath.¬†5.9 Dialysis using this method.¬†In this method, an electric sparks are hit between electrodes of metal that is immersed into the disperssion medium (Fig.¬†5.8).¬†

The intense heat created vapourizes the metal, and it expands to form particles with a colloidal shape. (c) Peptization could be described as the process of changing a precipitate into the form of colloidal sol through shaking by dispersion medium, in the presence of a tiny quantity of electrolyte. The electrolyte utilized for this purpose is known as peptizing agent. This technique is used typically to transform the freshly prepared precipitate to colloidal sol. When peptization is performed, the precipitate absorbs some of the electrons from the electrolyte onto its surface. This results in the formation of negative or positive charges on the precipitates that will eventually split into smaller particles that are that size as a collloid. When colloidal solutions are prepared, they typically contain a high quantity of electrolytes as well as other impurities that dissolve in water. The presence of electrolyte are essential to maintaining the integrity of the solution greater quantities cause coagulation. Therefore, it is essential to lower the amount of these impurities insoluble to a minimum. Top JEE coaching in Dimapur.

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The method used to reduce the quantity of impurities to a minimum called elimination of colloidal solution. The purification process of colloidal solution is accomplished by using these methods: (i) Dialysis: Dialysis is the process that removes a dissolving substance of a colloidal liquid diffusion via an appropriate membrane. Because particle (ions as well as tiny particles) in a real solution can travel through the animal membrane (bladder) or parchment paper or cellophane sheets but not particulate matter, the membrane may be used to dialysis. The device employed for this is known as dialyser. A bag with a suitable membranes that contain liquid colloidal is placed in a vessel , through which water that is fresh is always moving (Fig. 5.9). The ions and molecules diffuse across the membrane and into the surrounding water, and the pure colloidal solution remains in the background. (ii) Electro-dialysis: Typically dialysis is very slow. It is possible to speed it up through the use of an electrical field when the substance that dissolves within the colloidal impure solution only serves as an electrolyte. 

This process is referred to as electrodialysis.¬†The solution of colloidal particles is put in a bag made of a suitable membranes while water is removed.¬†Electrodes are placed inside the container as shown in Figure.¬†5.10.¬†The ions in colloidal solutions flow outwards to oppositely charged electrodes.¬†5.4.5 The purification process of Colloidal Solutions Fig.¬†5.8 Bredig’s arc method 2015-16(20/01/2015) Surface Chemistry 139 Eye Microscope Tyndall cone scattered light source of colloidal solution Figure.¬†5.11 Effect of Tyndall (iii) Ultrafiltration (Ultrafiltration) is the method of segregating the colloidal particles from solvents and soluble substances present within the solution using specially designed filters that can be permeable to any substance other than colloidal particles.¬†Colloidal particles are able to pass through regular filter paper due to they are big.¬†But, the pores of filters can be smaller by imbibing with collodion solution in order to stop the movement in colloidal particle.¬†Top¬†JEE coaching in Dimapur.

The standard collodion is composed of 4% of nitrocellulose mixed with a mixture of ether and alcohol. Ultra-filter papers can be made by soaking the filtering paper with a collodion solutionand it is then hardened by formaldehyde, and drying it. In this way, when using ultra-filter papers, the particles of colloidal are separated from the all other substances. Ultrafiltration is a slow procedure. To accelerate the process, suction or pressure is used. The colloidal particles that are left on the ultra-filter paper later stirred by new dispersion media (solvent) to produce an undiluted colloidal solution. Different properties that can be observed in colloidal solution are listed below: (i) Colligative properties because colloidal particles are bigger aggregates, the amount of particles present in the colloidal solution is smaller than an actual solution. Top JEE coaching in Dimapur. Therefore, the values of the colligative properties (osmotic pressure, lower the vapour pressure and depression of freezing point, and elevation of boiling points) are in a small range in comparison to those observed by real solutions with the similar concentrations. 

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Tyndall effect If a homogeneous mixture of solutions in darkness is viewed in its direction, it looks to be clear and, if seen from a position at exactly right angles with the direction of the light the beam of light, it looks completely dark. Solutions that are colloidal when viewed in the same manner can appear to be fairly transparent or clear when viewed with beam of light, but they exhibit an opalescence ranging from moderate to intense when observed at angles that are right to the path through the light beam, i.e. that the path of the beam gets illuminated by a blue light. This phenomenon was first discovered by Faraday and was later investigated in depth with Tyndall and is known by the term Tyndall effect. Its brighter cone light is known as Tyndall cone (Fig. 5.11). This Tyndall effect is caused by it being the case that particles of colloidal nature scatter light all over space. The reflection of light illuminates direction of light in the dispersion of colloidal particles. Top JEE coaching Centre in Dimapur.

The Tyndall effect is visible when a movie is projected inside the theater hall because of the scattering of light caused by smoke particles and dust that are found in the hall.¬†Tyndall effect can be observed only when two of the following conditions are met.¬†(i) The size of the dispersed particles is not more that the wavelength of light source as well as (ii) Refractive indexes of the dispersed and the dispersion medium are very different in terms of magnitude.¬†5.4.6 Characteristics of Colloidal Solutions 2015-16(20/01/2015) Chemistry 140 Tyndall effect is used to differentiate between a colloidal and a true solution.¬†Zsigmondy in 1903 employed the Tyndall effect to design an instrument known as the ultramicroscope.¬†A bright stream of light focused on the colloidal solution in glass vessels.¬†The focal point of the light is then observed using an optical microscope that is in a straight line towards the light beam.¬†Colloidal particles are seen as glowing stars against the dark background.Ultramicroscope doesn’t render particles themselves visible, but only detects the reflection of light by them.¬†

Therefore, the ultramicroscope doesn’t provide any details regarding the dimensions and shapes of particles colloidal.¬†(iii) Color The color of colloidal solutions is determined by its wavelength. emitted by dispersed particles.¬†Its light wavelength also is determined by the size and the nature of particles.¬†The color of colloidal solutions will change depending on the way that the viewer receives light.¬†For example, a solution of water and milk is blue when seen through the reflection of light, and red when it is viewed with transmitted light.¬†Gold sol that is the purest form is red As the size of the particles increase it becomes purple, and then blue and then gold.¬†(iv) Brownian movement when colloidal solutions can be examined with a powerful ultramicroscope they appear be in a continuous zig-zag movement across the area of view.¬†The motion was first noticed by Robert Brown, the British botanist Robert Brown, and is called Brownian movements (Fig.¬†5.12).¬†The motion is not dependent on how the colloid is formed, but is dependent on the dimensions of the particles as well as the its viscosity.¬†Less size, and smaller the viscosity, the faster the movement.¬†Top¬†JEE coaching Centre in Dimapur.

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The Brownian motion has been explained as a result of the unbalanced bombardment of particles by the molecules in the medium of dispersion. The Brownian movement is characterized by an effect of stirring that is unable to allow particles to settle, and is thereby at the root of stability for sols. (v) The charge on particles of colloidal origin: These particles have the charge of electricity. Its characteristics are same for all particles present in a colloidal solution, and can be negative or positive. A list of common sols and the nature of charge that their particles carry are listed below Hydrated metallic oxides e.g. Al2O3 .xH2O CrO3 .xH2O and Fe2O3 .xH2O and others. Basic dye stuffs, e.g., methylene blue sol. Haemoglobin (blood) Oxides, e.g., TiO2 sol. Metals e.g. Copper gold, silver sols. Metallic sulphides e.g. Sb2S3 as 2S3 , CdS sols. Acid dye stuffs e.g. Eosin, Congo Red Sols. Sols made of gum, starch gelatin, clay charcoal, and so on. Sols positively charged Sols that are negatively charged. 5.12 Brownian movement 2015-16(20/01/2015) 14 Surface Chemistry. This charge of sol particles is due at least one of the of the reasons such as. due to the capture of electrons by sol particles when they are electrodispersed of metals, due to the preferential absorption of ions from solutions and/or due to the formation of an electrochemical double layers. 

The adsorption of ions preferentially is the most well-known reason. Sol particles acquire negative or positive charge through the preferential adsorption of either neutral or positive ions. If more than two ions reside in the dispersion media it is common for them to be absorbed by the ion which is shared with the colloidal particle typically takes place. This is explained by using these examples: (a) When silver solution when added to the potassium iodide solution the silver iodide precipitated in the solution adsorbs Iodide ions out of the dispersion medium. The colloidal sol that is negatively charged is formed. When KI solution is added into AgNO3 solution, a positively charged sol is formed due to the adsorption Ag + ions in dispersion medium. Top JEE coaching Centre in Dimapur. AgI/I- AgI/Ag Negatively charged Positively attracted (b) In the event that FeCl3 is added to an excess of hot water and hot water, a positively charged solution of hydrated ferric oxide gets created due to the adsorption of Fe3+ions. When ferric chloride is added NaOH the negatively charged sol forms through the adsorption and resorption of OH ions. Fe2O3 .xH2O/Fe3+ Fe2O3 .xH2O/OHPositively charged, 

Negatively charged, having obtained a positive or negative charge via selective adhesion on the surface of the colloidal particle in the manner described earlier, this coating draws anti-ions from the medium, forming another layer, as illustrated below. AgI/I K+ AgI/Ag I The combination of two layers of opposing charges surrounding particles colloidal is referred to as Helmholtz electric double layer. According to current theories one layer of electrons are secured and is called a fixed layer, while the second layer is mobile and is referred to as diffused layer. Because separation of charge is the place where potential exists and charges, the charge of opposite charges in the diffused and fixed parts in the two layers result in a variance in the potential between the two layers. The potential difference between the fix layer as well as the diffused layer with opposite charges is known as the electrokinetic potential , also known as Zeta Potential. Top JEE coaching Centre in Dimapur.

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The presence of equally identical charges for colloidal particles responsible for stabilizing the colloidal solution since the forces of repulsive between charged particles that have the identical charges stop the colloidal particles from aggregating or coalescing as they get closer to each other. (vi) Electrophoresis The presence of colloidal particles charged is proven by an electrophoresis test. If an electric potential is applied to two platinum electrodes that are immersed in colloidal solutions, the colloidal particles are able to move toward either electrode. The motion of colloidal particles when subjected to an electric current is known as electrophoresis. Particles that are positively charged travel toward the cathode whereas negatively charged particles move away from it. Top  coaching Centre for JEE in Dimapur.

particles move towards the cathode. This is evident in the following experiment setup (Fig. 5.13). When electrophoresisis prevented, i.e. particle movement is stopped through a suitable method it occurs that the medium of dispersion starts to move within an electric force. This phenomenon is referred to as electroosmosis. (vii) Retention or coagulation: sols with lyophobic properties can be explained by the existence of charge upon colloidal particle. If, in some way, the charge is eliminated, particles will be closer to each other , and they will form an aggregate (or coagulate) and then settle in the gravity force. In the process of settlement colloidal particles is known as precipitation or coagulation of the sol. The coagulation process of sols with lyophobic properties is accomplished by the following methods: (i) By electrophoresis The colloidal particles travel toward electrodes that are charged in opposite directions, and are discharged and then precipitated. 

(ii) Mixing two sols with opposite charges Sols with opposite charges when mixed in close proportions, neutralize their charges, and then become fully or in part precipitated. The mixture of hydrated ferric dioxide (+ve sol) and arsenious sulfur (-ve sol) will result in precipitated form. This kind of coagulation is known as mutual co-coagulation. (iii) Through boiling when a sol is heated, the adsorbed surface is disturbed because of more collisions with molecules in the dispersion medium. This decreases the charge on particles and eventually causes them to settle down as precipitates. (iv) Through persistent dialysis: During prolonged dialysis, the traces of electrolyte that is present in the sol disappear virtually completely, and the colloids are unstable and then begin to coagulate. (v) Through the adding electrolytes: If the electrolyte in excess is added to the colloidal particles become precipitated. Top  coaching Centre for JEE in Dimapur.

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The reason for this is that colloids are in contact with ions that carry charges that are opposite to those they carry.¬†The result is neutralisation that leads to their cohesion.¬†The element responsible for neutralising the charge on particles is known as the coagulating the ion.¬†Negative ions cause precipitation from positively charged sol, and the reverse is true.¬†It has been found that the higher the valence of the ion flocculating added to the solution, the higher its ability to cause precipitation.¬†The term “coagulation” is derived from the the Hardy-Schulze rule.¬†When coagulating an ion that is negative the flocculating power is in the following order of: Ba2+ > Al3+Similar to the coagulation process of a positive sol, the flocculating strength is in the following order: [Fe(CN)6] 4- > PO4 3- SO4 2Cl – The minimal amount of electrolytes measured in millimololes per Liter needed to cause the precipitation of sol within two hours is known as the coagulating value.¬†Top¬† coaching Centre for¬†JEE¬†in Dimapur.

The less the amount required is, the greater the coagulating capacity of an Ion. Fig. 5.13: Electrophoresis 2015-16(20/01/2015) Surface Chemistry Coagulation of Sols with lyophilicity Two factors contribute to the stability and durability of the lyophilic sols. They are the charge and the solvation of colloidal particles. If these two elements are eliminated and a lyophilic sol is formed, it can be treated as a coagulant. This is accomplished (i) by using an electrolyte or (ii) by adding a solvent suitable for the task. When solvents like alcohol and Acetone are added to hydrophilic sols, dehydration of the dispersed phase takes place. In this case the presence of a small amount of electrolyte could cause the formation of coagulation. Colloids are protected Lyophilic sols tend to be more robust than sols that are lyophobic. This is because the colloids of lyophilic origin are highly solved, i.e., colloidal particles are covered with a thin layer of liquid within which they are dispersed. Lyophilic colloids possess the unique characteristic that protects colloids that are lyophobic. 

If a lyophilic solution is placed in the sol of a lyophobic the lyophilic particles create an outer layer over lyophobic particles, and protect them from electrolytes. Lyophilic colloids that are used for this purpose are known as protective colloids. They are colloidal systems that consist of liquids and liquids, i.e., the dispersion of finely separated droplets within another liquid. When a mixture made up of two impermeable or partially miscible liquids are shaken, the dispersion of the one liquid into the other liquid is created. This is known as an emulsion. In general, one or both liquids are water. There are two kinds of Emulsions. (i) Oil dispersed into the water (O/W kind) as well as (ii) water dispersed into oils (W/O kind). In the first case water acts as a dispersion medium. Examples of this kind of emulsion include milk and the disappearing of cream. In milk, the fat is dispersed into water. Top  coaching Centre for JEE in Dimapur. In the second method oil functions as a dispersing medium. Examples of this kind are cream and butter. 

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Emulsions made of oil in water can be unstable, and in some cases they split into two layers upon the surface. To stabilize an emulsion, a fourth component , referred to as an emulsifying agent, is typically added. The emulsifying agent creates an interfacial layer that is formed between the suspended particle and medium. The most common emulsifying agents used for emulsions of O/W are gums, proteins and synthetic and natural soaps and others. For W/O heavy metal salts of long chain alcohols, lampblack and more. Emulsions can be dilute with any quantity of dispersion medium. However the dispersed liquid, once mixed, creates a distinct layer. The droplets that form Emulsions are typically negatively charged and may be caused to form by electrolytes. They also exhibit Brownian movement as well as the Tyndall effects. Emulsions can be broken down into constituent liquids through cooling, heating, freezing, centrifuging, and so on. Top  coaching Centre for JEE in Dimapur.

A majority of the materials that we encounter in our daily lives include colloids. The food we consume, the clothes that are we put on, wood furniture we use, the homes we live in, and the newspapers we read are mostly made up of colloids. 5.5 Emulsions Water and oil within oil Oil. 5.14 Types of Emulsions 5.6 Colloids ColloidsColloids Around the world 2015-16(20/01/2015) Chemistry 144 High-voltage electrode (30000 voltages or more) Free of carbon particles. Precipitated ash Smoke The following are fascinating and interesting instances of colloids (i) Sky blue: Dust particles with the air suspended in water scatter blue light that is visible to our eyes, and the sky appears as if it is blue. (ii) fog rain, mist and fog: When a massive amount of air, which is a mixture of dust particles is cool to below its dewpoint, water vapors from the air settle on the surface of the particles, forming tiny droplets. 

These droplets that are colloidal, they continue to flounder in the air, forming fog or mist. Clouds are aerosols that contain small droplets of water suspended within air. Due to moisture in the upper air, colloidal droplets of water get larger and larger in size until they fall as rain. In some instances, rain falls when two clouds with opposite charges meet. There is a possibility to create fake rain through the throwing of electric sand or spraying sol carrying charges that are that is opposite to the charge on clouds from an aircraft. (iii) Food products like butter, milk Halwa, ice creams and fruit juices. They are all colloids in either form or. (iv) Blood is an insoluble solution made up of albuminoid. The styptic activity of ferric chloride and alum solution results in the blood coagulation, to form a clot, which will stop bleeding. Top  coaching Centre for JEE in Dimapur.

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(v) Soils Fertile soils are naturally colloidal in which humus functions as an anti-inflammatory colloid.¬†Because of their colloidal nature soils are able to absorb moisture and nourishment materials.¬†(vi) Delta formation The water of the river is a colloidal mixture of clay.¬†Sea water is a source of electrolytes.¬†When water from rivers meets sea and the electrolytes in sea water cause a coagulation of the clay’s colloidal solution leading to its deposition, resulting in the creation of delta.¬†Application of colloids Coloids are extensively utilized in industry.¬†Here are a few instances: (i) Electrical precipitation of smoke The smoke is a colloidal solution made up of solid particles like arsenic, carbon dust, etc. In air.¬†Smoke, before it exits the chimney, passes through a chamber that contains plates that have a charge contrary to the one the smoke particles carry.¬†The particles that come into contact with the plates loose their charges and are precipitated.¬†Top¬† coaching Centre for¬†JEE¬†in Dimapur.

The particles then settle to the ground in the chamber. The precipitator is referred to as Cottrell precipitator (Fig.5.15). (ii) Water purification: Water that comes from natural sources usually has suspended impurities. Alum is added into the water to break down the suspended impurities, making water safe for drinking. (iii) Medical: The majority of the medications come from colloidal substances. For instance, argyrol can be silver sol, which is commonly that is used to make an eye cream. Colloidal antimony is employed to treat Kalaazar. Gold colloidal is utilized for intramuscular injections. Milk of magnesia is an emulsion that is used to treat stomach issues. The effectiveness of colloidal medicine is due to their Cottrell smoke precipitator large surface area , and can therefore be easily absorbed. (iv) Tanning Animal hides contain colloidal particles in the natural world. 

When a hidethat contains positively charged particles is submerged in tannin, which is a substance that contains positively charged colloidal particles mutual coagulation occurs.¬†This causes the leather’s ability to harden.¬†This is referred to as tanning.¬†Chromium salts are also utilized to replace tannin.¬†(v) Cleaning actions of detergents and soaps This is already explained in section 5.4.3.¬†(vi) Photographic films and plates Photographic films or plates are created using an emulsion made of the light-sensitive silver bromide in gelatin on cellsuloid or glass films.¬†(vii) Industry of rubber: Latex is a colloidal solution of rubber particles that positively charged.¬†It is made by the the coagulation process of latex.¬†(viii) Products for industrial use: Inks, paints and synthetic plastics and graphite lubricants as well as cement and more. All colloidal solutions.¬†Top¬† coaching Centre for¬†JEE¬†in Dimapur.