NCERT Solutions Class 12 Chemistry Chapter 5
NCERT Solutions Class 12 Chemistry Chapter 5 Surface Chemistry
NCERT Solutions Class 12 Chemistry Chapter 5 Surface Chemistry is summarised by experts at Extramarks to benefit the students studying in class 12. Students preparing for CBSE Class 12 examination must consider NCERT Solutions to understand the chapter. The Surface Chemistry chapter shows the role of adsorption, kinds of adsorption, pressure effects, and temperature effects on the surface and explains a few topics. The study material provided by Extramarks for NCERT Solutions Class 12 Chemistry Chapter 5 will be an excellent help for CBSE students.
Key Topics Covered In NCERT Solutions Class 12 Chemistry Chapter 5 Surface Chemistry
The table below details the class 12 chemistry ch 5 NCERT solutions. Let’s have an overview of the constituent topics of this chapter.
|5.4||Classification of Colloids|
|5.6||Colloids around us|
Students may click on the topics to access Chapter 5 Chemistry Class 12 NCERT solutions for the respective exercise. A brief of the various topics that come under the NCERT Solutions Class 12 Chemistry Chapter 5 is given below.
Surface Chemistry works with the chemical reactions at the surface or interface. There is a broad range of practical applications which involves surface chemistry. From the production of high vacuum to the manufacturing of Gas Masks, surface chemistry principles are used widely. It is also used to understand the catalyst reactions, Tyndall effect and Brownian movement, used for various applications.
The accumulation of attracting and keeping the molecule of a substance on the surface of a solid is called adsorption. This results in an enhanced concentration on the surface than in bulk. The adsorption of a gas on a solid material depends on the following factors: surface area of the solid, temperature of the gas, nature of the gas, the pressure of the gas, and nature of the solid.
Adsorption is the first exercise under NCERT Solutions Class 12 Chemistry Chapter 5 and includes
- Adsorbate: It is the substance that is being adsorbed on the surface of another substance.
- Adsorbent: It is the substance present in bulk, on the surface of which adsorption takes place.
- Desorption: In this process of removing an adsorbed substance from a surface on which it is adsorbed.
- Adsorption: As per NCERT Solutions Class 12 Chemistry Chapter 5, absorption is the phenomenon in which a substance is uniformly distributed throughout the bulk of the solid. The concentration is the same throughout the bulk of the solid.
- Sorption: When adsorption and absorption take place at the same time, it is known as sorption.
- Enthalpy or heat of adsorption: when adsorption happens with the release of energy, that is exothermic in nature. The enthalpy change for the adsorption of a mole of an adsorbate on the surface of the adsorbent is known as enthalpy.
Types of adsorption: Types of adsorption mentioned in NCERT Solutions Class 12 Chemistry Chapter 5 are as under.
- Physical adsorption: When adsorbate is held on a surface of the adsorbent by weak van der Waals’ forces, the adsorption is known as physical adsorption or physisorption. It is non-specific and reversible. The amount of gas depends upon nature. The scope of adsorption increases with an increase in surface area, like porous and finely divided metals are suitable adsorbents.
- Chemical adsorption or chemisorption: If the forces holding the adsorbate are as strong as in chemical bonds, the adsorption process is called chemical adsorption of chemisorption. It is definite and irreversible. The exact amount of gas adsorbed is not related to the critical temperature of the gas. It also increases with surface area. There is a strong force of attraction as same as to chemical bond. It forms unimolecular layers.
Under this section of NCERT Solutions Class 12 Chemistry Chapter 5, students will learn about catalysis. All reactants need to overcome specific energy; activation energy is the difference between the energy of the transition state and the reactant species. Some reactant molecules have sufficient kinetic energy to overcome this energy barrier, whereas others don’t. Therefore, not all reactions happen at the same rate in general conditions. Thus, specific reagents are added, lowering the required activation energy to convert reactants to products. These reagents are called catalysts, and this process of reducing the activation energy is called catalysis.
Catalysis of chemical reactions is divided into two categories:
- Homogeneous Catalysis: The Homogeneous catalysis of chemical reactions is a process where the reactants are involved in the reaction, and the catalyst is in the same phase. Ex: hydrolysis of glucose in the presence of acid.
- Heterogeneous Catalysis: The Heterogeneous catalysis of chemical reactions is a process where the reactants involved in the reaction, and the catalyst, are in different phases. Forex: reaction of hydrogen and nitrogen in iron to form ammonia.
Mechanism of Heterogeneous Catalysis of Chemical Reactions: Students will also learn the mechanism of heterogeneous catalysis of chemical reactions under NCERT Solutions Class 12 Chemistry Chapter 5. The modern theory of adsorption has a five-step mechanism for the catalysis of chemical reactions. These steps are as follows:
- General Introduction and diffusion of reactant molecules on the catalytic surface.
- Adsorption of molecules of reactants on the catalytic surface.
- Formation of intermediate on a catalytic surface by a chemical reaction between the reactant molecules.
- Desorption of product molecules from the catalytic.
- Diffusion of product molecules away from the catalytic surface to form final products.
What is catalysis? A catalyst is defined as a substance that increases the rate of a chemical reaction without changing itself. The process by which a catalyst enhances the reaction rate is known as catalysis.
How do catalysts work? For reactants to react and give a final product, reactant molecules have threshold energy, and the exact number of molecules with this energy should also be more than a threshold value. This energy is known as activation energy.
Example of some heterogeneous catalysts: Under the Oxidation of sulphur dioxide into sulphur trioxide in front of (platinum metal or vanadium pentoxide )as a catalyst, reactants are in a gaseous state while the catalyst is in a solid state.
The NCERT Solutions Class 12 Chemistry Chapter 5 also defines enzymes. Enzymes are nitrogenous compounds that plants and animals generate. It is a high molecular mass protein molecule and forms colloidal solutions with water. It is a very effective catalyst. They catalyse many reactions in animals’ and plants’ bodies to maintain life processes; Thus, enzymes are called biochemical catalysts.
Enzyme catalysed Reactions: Decomposition of Urea converts into Ammonia and Carbon Dioxide. Urease enzyme is used as an enzyme catalyst.
5.4 Classification of colloids
Under NCERT Solutions Class 12 Chemistry Chapter 5, Colloids are classified:
Based on the physical state of the dispersed phase and dispersed medium:
|S.No||Dispersed Phase||Dispersed Medium||Name of Colloid||Examples|
|2.||Solid||Liquid||Sol||Muddy water, Paint, cell fluids|
|4.||Liquid||Solid||Gel||Cheese, butter, jelly|
|5.||Liquid||Liquid||Emulsion||Milk, Hair cream|
|6.||Liquid||Gas||Aerosol||Fog, mist, cloud|
|7.||Gas||Solid||Solid Foam||Pumice Stone|
|8.||Gas||Liquid||Foam||Froth, soap lather|
Based on the nature of Interaction Between the Dispersed Phase and Dispersed Medium
- Lyophilic Colloids(liquid loving): A few substances can form colloids directly by adding them to a suitable liquid(dispersion medium). These colloids are called lyophilic colloids. Examples of these substances are gum, gelatine, starch and rubber. It is also known as Reversible sols.
- Lyophobic colloids (liquid hating): A few substances cannot form colloids by directly adding them to a liquid. Colloidal sols are made up of unique methods known as lyophobic colloids. Examples of these substances are metals and metal sulphides. They are also known as Irreversible colloids.
Based on Types of Particles of the Dispersed Phase-
- Multimolecular Colloids: Many particles(atoms or molecules) of the dispersed phase combine to form species with colloidal particle size. These colloids are known as multimolecular colloids. Eg-gold sol.
- Macromolecular colloids: Substances with large molecules in suitable solvents form solutions, but these macromolecules might be in the colloidal range. These solutions are known as macromolecular colloids and resemble real solutions in many ways. E.g., Starch, Cellulose.
- Associated Colloids: A few substances at high concentrations act as colloids due to the formation of aggregates. Therefore at low concentrations, they behave like normal strong electrolytes. These aggregates formed are called micelles. Such colloids are called associated colloids.
Properties of Colloids- Brownian Movement: Under NCERT Solutions class 12 Chemistry chapter 5 Brownian movement can be explained as the ceaseless zigzag movement of the colloidal particles in a colloidal solution. It is based on the size of the particle’s viscosity of the colloid. This movement is responsible for the stability of sols.
Emulsions are colloids where both the dispersion phase and dispersion medium are liquids. These two liquids are immiscible or partially miscible. Generally, one of the liquids is water. There are two types of emulsions.
Oil dispersed in water (o/w type)- Water acts as a dispersion medium, for example –milk and vanishing cream.
Water dispersed in oil (w/o type)- Oil acts as a dispersion medium, For example- Butter, Cream.
5.6 Applications of Colloids
Under NCERT Solutions Class 12 Chemistry Chapter 5 Exercise 5.5, students may study the application of colloids.
- Purification drinking water – Alum is a mix of impure water to thicken the suspended impurities and make water fit for drinking.
- Medicines – Many medicines are colloidal in nature. Colloidal medicines are more effective. E.g., Argyrol is a silver sol used as an eye lotion.
- Industrial products- Paints, inks, synthetic plastics, rubber, cement, and graphite lubricants are all colloids.
Students may refer to Extramarks study material that includes revision notes, important questions, and sample questions pertaining to NCERT Solutions class 12 Chemistry chapter 5.
NCERT Solutions Class 12 Chemistry Chapter 5 Exercise & Solutions
NCERT Solutions Class 12 Chemistry Chapter 5 Exercise and Solutions are vital aspects of the study material that students refer to. The solutions provided in this section help students understand how to answer important questions to ensure that they have covered all aspects of the topic.
Some of the essential exercise questions and answers for NCERT Solutions Class 12 Chemistry chapter 5 include topics such as Demulsification, Coagulation, Dialysis colloidal particles, and more. The exercise and answer solutions provided by Extramarks are detailed in nature to ensure that students can understand the concept without having to depend on teachers. They prepare students to face questions of any difficulty level during examinations.
NCERT Solutions Class 12 Chemistry Chapter 5 is explained in detail by the experts of Extramarks. Students may refer to the various study material provided, which concentrates more on the key points. In addition to Chapter 5, students can access NCERT Solution for all other Chemistry chapters of Class 12. Furthermore, students can click on the likes provided below to access the study material of different classes and subjects.
Q.1 How do emulsifiers stabilise emulsion? Name two emulsifiers.
An emulsion is a colloidal solution of two immiscible liquids in which one of the liquids acts as the dispersed phase and the other acts as the dispersion medium. An emulsifiers or emulsifying agent is a substance that is added to an emulsion to stabilise it. For example, proteins, gums, natural and synthetic soaps are the emulsifier for the oil in water emulsions. Heavy metal salts of fatty acids, long chain alcohols, lamp-black are the emulsifiers for the water in oil emulsions.
Soaps and detergents are the commonly used emulsifiers.
Q.2 Distinguish between the meaning of the terms adsorption and absorption.
Give one example of each.
Adsorption is a surface phenomenon of accumulation of molecules of a substance at the surface rather than in the bulk of a solid or liquid. The substance that gets adsorbed is called the ‘adsorbate’ and the substance on whose surface the adsorption takes place is called the ‘adsorbent’. Here, the concentration of the adsorbate on the surface of the adsorbent increases. In adsorption, the substance gets concentrated at the surface only. It does not penetrate through the surface to the bulk of the solid or liquid. For example, when we dip a chalk stick into an ink solution, only its surface becomes coloured. If we break the chalk stick, it will be found to be white from inside.
On the other hand, the process of absorption is a bulk phenomenon. In absorption, the substance gets uniformly distributed throughout the bulk of the solid or liquid.
Q.3 What is the difference between physisorption and chemisorption?
|1.||In this type of adsorption, the adsorbate is attached to the surface of the adsorbent with weak van der Waal’s forces of attraction.||In this type of adsorption, strong chemical bonds are formed between the adsorbate and the surface of the adsorbent.|
|2.||No new compound is formed in the process.||New compounds are formed at the surface of the adsorbent.|
|3.||It is generally found to be reversible in nature.||It is usually irreversible in nature.|
|4.||Enthalpy of adsorption is low as weak van der Waal’s forces of attraction are involved. The values lie in the range of 20-40 kJmol -1.||Enthalpy of adsorption is high as chemical bonds are formed. The values lie in the range of 40-400 kJmol-1.|
|5.||It is favoured by low temperature conditions.||It is favoured by high temperature conditions.|
|6.||It is an example of multi-layer adsorption.||It is an example of mono-layer adsorption.|
Q.4 Give reason why a finely divided substance is more effective as an adsorbent.
Adsorption is a surface phenomenon. Therefore, adsorption is directly proportional to the surface area. A finely divided substance has a large surface area. Both physisorption and chemisorption increase with an increase in the surface area. Hence, a finely divided substance behaves as a good adsorbent.
Q.5 What are the factors which influence the adsorption of a gas on a solid?
There are various factors that affect the rate of adsorption of a gas on a solid surface.
(1) Nature of the gas:
Easily liquefiable gases such as NH3, HCl etc. are adsorbed to a great extent in comparison to gases such as H2, O2 etc. This is because Van der Waal’s forces are stronger in easily liquefiable gases.
(2) Surface area of the solid
The greater the surface area of the adsorbent, the greater is the adsorption of a gas on the solid surface.
(3) Effect of pressure
Adsorption is a reversible process and is accompanied by a decrease in pressure. Therefore, adsorption increases with an increase in pressure.
(4) Effect of temperature
Adsorption is an exothermic process. Thus, in accordance with Le-Chatelier’s principle, the magnitude of adsorption decreases with an increase in temperature.
Q.6 What is an adsorption isotherm? Describe Freundlich adsorption isotherm.
The plot between the extent of adsorption x/m against the pressure of gas (P) at constant temperature (T) is called the adsorption isotherm.
Freundlich adsorption isotherm: Freundlich adsorption isotherm gives an empirical relationship between the quantity of gas adsorbed by the unit mass of solid adsorbent and pressure at a specific temperature. From the given plot it is clear that at pressure Ps, x/m reaches the maximum value. Ps is called the saturation pressure. Three cases arise from the graph now.
Case I- At low pressure: The plot is straight and sloping, indicating that the pressure is directly proportional to
Q.7 What do you understand by activation of adsorbent? How is it achieved?
By activating an adsorbent, we tend to increase the adsorbing power of the adsorbent. Some ways to activate an adsorbent are:
(i) By increasing the surface area of the adsorbent. This can be done by breaking it into smaller pieces or powdering it.
(ii) Some specific treatments can also lead to the activation of the adsorbent. For example, wood charcoal is activated by heating it between 650 K and 1330 K in vacuum or air. It expels all the gases absorbed or adsorbed and thus, creates a space for adsorption of gases.
Q.8 What role does adsorption play in heterogeneous catalysis?
A catalytic process in which the catalyst and the reactants are present in different phases is known as a heterogeneous catalysis. This heterogeneous catalytic action can be explained in terms of the adsorption theory. The mechanism of catalysis involves the following steps:
(i) Adsorption of reactant molecules on the catalyst surface.
(ii) Occurrence of a chemical reaction through the formation of an intermediate.
(iii) De-sorption of products from the catalyst surface
(iv) Diffusion of products away from the catalyst surface. In this process, the reactants are usually present in the gaseous state and the catalyst is present in the solid state. Gaseous molecules are then adsorbed on the surface of the catalyst. As the concentration of reactants on the surface of the catalyst increases, the rate of reaction also increases. In such reactions, the products have very less affinity for the catalyst and are quickly desorbed, thereby making the surface free for other reactants.
Q.9 Why is adsorption always exothermic?
Adsorption is always exothermic. This statement can be explained in two ways.
(i) Adsorption leads to a decrease in the residual forces on the surface of the adsorbent. This causes a decrease in the surface energy of the adsorbent. Therefore, adsorption is always exothermic.
(ii) ∆H of adsorption is always negative. When a gas is adsorbed on a solid surface, its movement is restricted leading to a decrease in the entropy of the gas i.e., ∆S is negative. Now for a process to be spontaneous, ∆G should be negative.
Since ∆S is negative, ∆H has to be negative to make ∆G negative. Hence, adsorption is always exothermic.
Q.10 How are the colloidal solutions classified on the basis of physical states of the dispersed phase and dispersion medium?
One criterion for classifying colloids is the physical state of the dispersed phase and dispersion medium. Depending upon the type of the dispersed phase and dispersion medium (solid, liquid, or gas), there can be eight types of colloidal systems.
|Dispersed phase||Dispersion medium||Type of colloid||Example|
|7.||Gas||Solid||Solid foam||Pumice stone|
Q.11 Discuss the effect of pressure and temperature on the adsorption of gases on solids.
Effect of pressure
Adsorption is a reversible process and is accompanied by a decrease in pressure. Therefore, adsorption increases with an increase in pressure.
Effect of temperature
Adsorption is an exothermic process. Thus, in accordance with Le-Chatelier’s principle, the magnitude of adsorption decreases with an increase in temperature.
Q.12 What are lyophilic and lyophobic sols? Give one example of each type. Why are hydrophobic sols easily coagulated?
(i) Lyophilic sols:
Colloidal sols that are formed by mixing substances such as gum, gelatin, starch, etc. with a suitable liquid (dispersion medium) are called lyophilic sols. These sols are reversible in nature i.e., if two constituents of the sol are separated by any means (such as evaporation), then the sol can be prepared again by simply mixing the dispersion medium with the dispersion phase and shaking the mixture.
(ii) Lyophobic sols:
When substances such as metals and their sulphides etc. are mixed with the dispersion medium, they do not form colloidal sols. Their colloidal sols can be prepared only by special methods. Such sols are called lyophobic sols. These sols are irreversible in nature. For example: sols of metals.
Now, the stability of hydrophilic sols depends on two things- the presence of a charge and the solvation of colloidal particles. On the other hand, the stability of hydrophobic sols is only because of the presence of a charge. Therefore, the latter are much less stable than the former. If the charge of hydrophobic sols is removed (by addition of electrolytes), then the particles present in them come closer and form aggregates, leading to precipitation.
Q.13 What is the difference between multimolecular and macromolecular colloids? Give one example of each. How are associated colloids different from these two types of colloids?
(i) In multi-molecular colloids, the colloidal particles are an aggregate of atoms or small molecules with a diameter of less than 1 nm. The molecules in the aggregate are held together by van der Waal’s forces of attraction. Examples of such colloids include gold sol and sulphur sol.
(ii) In macro-molecular colloids, the colloidal particles are large molecules having colloidal dimensions. These particles have a high molecular mass. When these particles are dissolved in a liquid, sol is obtained. For example: starch, nylon, cellulose, etc.
(iii) Certain substances tend to behave like normal electrolytes at lower concentrations. However, at higher concentrations, these substances behave as colloidal solutions due to the formation of aggregated particles. Such colloids are called aggregated colloids.
Q.14 What are enzymes? Write in brief the mechanism of enzyme catalysis.
Enzymes are basically protein molecules of high molecular masses. These form colloidal solutions when dissolved in water. These are complex, nitrogenous organic compounds produced by living plants and animals. Enzymes are also called ‘biochemical catalysts’.
Mechanism of enzyme catalysis:
On the surface of the enzymes, various cavities are present with characteristic shapes. These cavities possess active groups such as −NH2, −COOH, etc. The reactant molecules having a complementary shape fit into the cavities just like a key fits into a lock. This leads to the formation of an activated complex. This complex then decomposes to give the product.
Step 1: E + S → ES≠
Step 2: ES≠ → E + P
Q.15 How are colloids classified on the basis of
(i) Physical states of components
(ii) Nature of dispersion medium and
(iii) Interaction between dispersed phase and dispersion medium?
Colloids can be classified on various bases:
(i) On the basis of the physical state of the components (by components we mean the dispersed phase and dispersion medium). Depending on whether the components are solids, liquids, or gases, we can have eight types of colloids.
(ii) On the basis of the dispersion medium, sols can be divided as:
|Dispersion medium||Name of sol|
|Water||Aquasol or hydrosol|
(iii) On the basis of the nature of the interaction between the dispersed phase and dispersion medium, the colloids can be classified as lyophilic (solvent attracting) and lyophobic (solvent repelling).
Q.16 Explain what is observed
(i) When a beam of light is passed through a colloidal sol.
(ii) An electrolyte, NaCl is added to hydrated ferric oxide sol.
(iii) Electric current is passed through a colloidal sol?
(i) When a beam of light is passed through a colloidal solution, then scattering of light is observed. This is known as the Tyndall effect. This scattering of light illuminates the path of the beam in the colloidal solution.
(ii) When NaCl is added to ferric oxide sol, it dissociates to give Na+ and Cl– ions. Particles of ferric oxide sol are positively charged. Thus, they get coagulated in the presence of negatively charged Cl– ions.
(iii) The colloidal particles are charged and carry either a positive or negative charge. The dispersion medium carries an equal and opposite charge. This makes the whole system neutral. Under the influence of an electric current, the colloidal particles move towards the oppositely charged electrode. When they come in contact with the electrode, they lose their charge and coagulate.
Q.17 What are emulsions? What are their different types? Give example of each type.
The colloidal solution in which both the dispersed phase and dispersion medium are liquids is called an emulsion. There are two types of emulsions:
(a) Oil in water type:
Here, oil is the dispersed phase while water is the dispersion medium. For example: milk, vanishing cream, etc.
(b) Water in oil type:
Here, water is the dispersed phase while oil is the dispersion medium. For example: cold cream, butter, etc.
Q.18 Give four uses of emulsions.
Four uses of emulsions:
(i) Cleansing action of soaps is based on the formation of emulsions.
(ii) Digestion of fats in intestines takes place by the process of emulsification.
(iii) Antiseptics and disinfectants when added to water form emulsions.
(iv) The process of emulsification is used to make medicines.
Q.19 Action of soap is due to emulsification and micelle formation. Comment.
The cleansing action of soap is due to emulsification and micelle formation. Soaps are basically sodium and potassium salts of long chain fatty acids, R-COO-Na+. The end of the molecule to which the sodium is attached is polar in nature, while the alkyl-end is non-polar. Thus, a soap molecule contains a hydrophilic (polar) and a hydrophobic (non-polar) part.
When soap is added to water containing dirt, the soap molecules surround the dirt particles in such a manner that their hydrophobic parts get attached to the dirt molecule and the hydrophilic parts point away from the dirt molecule. This is known as micelle formation. Thus, we can say that the polar group dissolves in water while the non-polar group dissolves in the dirt particle. Now, as these micelles are negatively charged, they do not coalesce and a stable emulsion is formed.
Q.20 Give four examples of heterogeneous catalysis.
(i) Oxidation of sulphur dioxide to form sulphur trioxide. In this reaction, Pt acts as a catalyst.
Q.21 What do you mean by activity and selectivity of catalysts?
(a) Activity of a catalyst:
The activity of a catalyst is its ability to increase the rate of a particular reaction. Chemisorption is the main factor in deciding the activity of a catalyst. The adsorption of reactants on the catalyst surface should be neither too strong nor too weak. It should just be strong enough to make the catalyst active.
(b) Selectivity of the catalyst:
The ability of the catalyst to direct a reaction to yield a particular product is referred to as the selectivity of the catalyst. For example, by using different catalysts, we can get different products for the reaction between H2 and CO.
Q.22 Describe some features of catalysis by zeolites.
Zeolites are alumino-silicates that are micro-porous in nature. Zeolites have a honeycomb-like structure, which makes them shape-selective catalysts. They have an extended 3D-network of silicates in which some silicon atoms are replaced by aluminium atoms, giving them an Al−O−Si framework. The reactions taking place in zeolites are very sensitive to the pores and cavity size of the zeolites. Zeolites are commonly used in the petrochemical industry.
Q.23 What is shape selective catalysis?
A catalytic reaction which depends upon the pore structure of the catalyst and on the size of the reactant and the product molecules is called shape-selective catalysis. For example, catalysis by zeolites is a shape-selective catalysis. The pore size present in the zeolites ranges from 260-740 pm. Thus, molecules having a pore size more than this cannot enter the zeolite and undergo the reaction.
Q.24 Explain the following terms:
(i) Electrophoresis (ii) Coagulation
(iii) Dialysis (iv) Tyndall effect.
The movement of colloidal particles under the influence of an applied electric field is known as electrophoresis. Positively charged particles move to the cathode, while negatively charged particles move towards the anode. As the particles reach oppositely charged electrodes, they become neutral and get coagulated.
The process of settling down of colloidal particles i.e., conversion of a colloid into a precipitate is called coagulation.
The process of removing a dissolved substance from a colloidal solution by the means of diffusion through a membrane is known as dialysis. This process is based on the principle that ions and small molecules can pass through animal membranes unlike colloidal particles.
(iv) Tyndall effect:
When a beam of light is allowed to pass through a colloidal solution, it becomes visible like a column of light. This is known as the Tyndall effect. This phenomenon takes place as particles of colloidal dimensions scatter light in all directions.
Q.25 What are micelles? Give an example of a micellers system.
Micelle formation is done by substances such as soaps and detergents when dissolved in water. The molecules of such substances contain a hydrophobic and a hydrophilic part. When present in water, these substances arrange themselves in spherical structures in such a manner that their hydrophobic parts are present towards the centre, while the hydrophilic parts are pointing towards the outside (as shown in the given figure). This is known as micelle formation.
Q.26 Comment on the statement that “colloid is not a substance but a state of substance”.
Common salt (a typical crystalloid in an aqueous medium) behaves as a colloid in a benzene medium. Hence, we can say that a colloidal substance does not represent a separate class of substances. When the size of the solute particle lies between 1 nm and 1000 nm, it behaves as a colloid.
Hence, we can say that colloid is not a substance but a state of the substance which is dependent on the size of the particle. A colloidal state is intermediate between a true solution and a suspension.
Q.27 Explain the terms with suitable examples:
(i) Alcosol (ii) Aerosol (iii) Hydrosol
A colloidal solution having alcohol as the dispersion medium and a solid substance as the dispersed phase is called an alcosol.
For example: colloidal sol of cellulose nitrate in ethyl alcohol is an alcosol.
A colloidal solution having a gas as the dispersion medium and a solid as the dispersed phase is called an aerosol.
For example: fog
A colloidal solution having water as the dispersion medium and a solid as the dispersed phase is called a hydrosol.
For example: starch sol or gold sol
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Chapter 5 chemistry Class 12 NCERT solutions help students understand the basic concepts of solutions and give a detailed explanation of various laws and formulas under the chapter. It allows students to study for the exams without depending on someone to explain. Students may refer to NCERT Solutions Class 12 Chemistry Chapter 5 on Extramarks.
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