Samacheer Kalvi Class 12 Chemistry Solutions Chapter 10 Surface Chemistry

Question 11. Addition of Alum purifies water. Why?
Answer: Adding alum to water helps purify it because alum contains aluminum ions (\( \text{Al}^{3+} \)). These ions cause the suspended impurities in the water to clump together, a process called coagulation. This makes the impurities heavy enough to settle down, leaving the water clean. This is why alum is commonly used to treat drinking water.
In simple words: Alum has special parts that make dirt in water stick together and sink, so the water becomes clean.

🎯 Exam Tip: When explaining water purification, remember to mention "coagulation" and the role of multivalent ions (like \( \text{Al}^{3+} \)) in settling suspended particles.

Question 12. What are the factors which influence the adsorption of a gas on a solid?
Answer: The adsorption of a gas onto a solid surface is affected by several things:
1. **Nature of the gas:** Gases that can be easily turned into liquid (liquefiable) like ammonia (\( \text{NH}_3 \)) or hydrogen chloride (\( \text{HCl} \)) are adsorbed more readily. This happens because the attractive forces (van der Waals forces) between them and the solid are stronger. These gases have higher critical temperatures, which means they are more likely to interact with the solid surface.
2. **Surface area of the solid:** The more surface area a solid has, the more space there is for gas molecules to stick. So, a larger surface area leads to more adsorption.
3. **Effect of pressure:** Adsorption is a process that can go both ways (reversible) and usually involves a decrease in pressure. Increasing the pressure generally causes more gas to be adsorbed onto the solid.
4. **Effect of temperature:** Adsorption is an exothermic process, meaning it releases heat. According to Le Chatelier's principle, if you increase the temperature, the adsorption amount will decrease because the system tries to oppose the change by shifting away from the heat-producing process.
In simple words: How much gas sticks to a solid depends on the type of gas, how much surface the solid has, the pressure, and the temperature. Some gases stick better, bigger surfaces hold more, higher pressure helps, but higher heat makes less gas stick.

🎯 Exam Tip: Always remember that adsorption is usually an exothermic process, making temperature an inverse factor in its extent. Also, connect easily liquefiable gases with stronger van der Waals forces.

Question 13. What are enzymes? Write a brief note on the mechanism of enzyme catalysis.
Answer: Enzymes are complex protein molecules with special three-dimensional shapes. They act as catalysts for chemical reactions inside living organisms, helping them happen faster. Enzymes are often found in a colloidal state and are very specific about which reactions they can speed up. This high specificity is due to their unique active sites.
The way enzymes speed up reactions is explained by the **lock and key mechanism**:
1. **Specificity:** Enzymes are very particular. Each enzyme usually works only for a specific type of reaction or a specific molecule.
2. **Active Sites:** This specificity comes from their "active sites," which are like uniquely shaped pockets or cavities on the enzyme. Only a molecule with the perfect shape (the "substrate") can fit into this active site, just like a key fits into its lock. This perfect fit creates an enzyme-substrate complex, which is crucial for the reaction.
3. **Product Formation:** Once the substrate properly fits into the enzyme's active site, the enzyme helps the substrate molecules react. This process usually happens in two main steps to form the product.
4. **Product Release:** After the reaction, the new product molecules no longer fit well into the active site. So, they leave the enzyme surface. This frees up the active site, allowing the enzyme to be used again for another substrate molecule.
The mechanism involves two main steps:
**Step 1: Formation of the enzyme-substrate complex**
\[ \text{E (Enzyme)} + \text{S (Substrate)} \rightleftharpoons \text{ES (Complex)} \]
This is a fast and reversible reaction.
**Step 2: Dissociation of the enzyme-substrate complex to form product**
\[ \text{ES (Complex)} \rightarrow \text{E (Enzyme)} + \text{P (Product)} \]
This is the slow step reaction. The rate of product formation depends on the concentration of the enzyme-substrate complex.
In simple words: Enzymes are special proteins that speed up reactions in living things. They work like a lock and key: only the right molecule (key) can fit into the enzyme's special spot (lock), allowing the reaction to happen quickly. Once the reaction is done, the new product leaves, and the enzyme is ready for another job. This happens in two steps: first, the enzyme and molecule join, then they break apart into the enzyme and a new product.

🎯 Exam Tip: When describing enzyme catalysis, clearly explain "active site" and the "lock and key" analogy, as these are core concepts. Mentioning their protein nature and specificity, along with the two-step reaction mechanism, is also key.

Question 14. What do you mean by activity and selectivity of catalyst?
Answer: The effectiveness of a catalyst is described by two main properties:
1. **Activity of Catalyst:** This refers to a catalyst's ability to increase the speed of a particular reaction. Chemisorption (when reactants stick to the catalyst surface) is the most important factor for a catalyst's activity. The bonding between reactants and the catalyst surface should be just right-not too strong (so products can leave) and not too weak (so reactants can bind). A good catalyst helps reactants interact efficiently.
2. **Selectivity of the catalyst:** This is the catalyst's ability to direct a reaction towards making a specific product, even when other products are possible. For example, by using different catalysts, the same reactants (like \( \text{H}_2 \) and \( \text{CO} \)) can produce entirely different products:
(a) \( \text{CO(g)} + 3\text{H}_2\text{(g)} \xrightarrow{\text{Ni}} \text{CH}_4\text{(g)} + \text{H}_2\text{O(g)} \)
(b) \( \text{CO(g)} + 2\text{H}_2\text{(g)} \xrightarrow{\text{Cu/ZnO, CrO}_3} \text{CH}_3\text{OH(g)} \)
(c) \( \text{CO(g)} + \text{H}_2\text{(g)} \xrightarrow{\text{Cu}} \text{HCHO(g)} \)
The type of catalyst determines which product is formed, making it highly selective.
In simple words: A catalyst's "activity" means how well it speeds up a reaction, and its "selectivity" means how well it guides a reaction to make only one specific product out of many possible ones. Different catalysts can make different products from the same starting materials.

🎯 Exam Tip: Remember to differentiate activity (rate enhancement) from selectivity (product direction). Use the example of \( \text{CO} \) and \( \text{H}_2 \) reactions with different catalysts to illustrate selectivity clearly.

Question 15. Describe some features of catalysis by Zeolites.
Answer: Zeolites are special catalysts with unique features:
1. **Structure:** Zeolites are microporous, crystalline materials called aluminosilicates. They are made from silicon and aluminum tetrahedra, which form a cage-like structure with tiny pores.
2. **Types:** There are around 50 types of natural zeolites and about 150 synthetic ones. In zeolites, silicon is tetravalent and aluminum is trivalent. The zeolite framework has a negative charge. This negative charge is balanced by positive ions like \( \text{H}^+ \) or \( \text{Na}^+ \).
3. **Acidic Catalysis:** Zeolites often act as solid acids. They are widely used in the petrochemical industry for important processes like cracking heavy hydrocarbons into gasoline and diesel. The acidic sites within the pores facilitate these reactions.
4. **Basic Catalysis:** Some zeolites, especially those with \( \text{Na}^+ \) ions, can also be used for basic catalysis.
5. **Shape Selectivity:** One of their most important properties is "shape selectivity." This means that reactions only happen inside the tiny pores of the zeolite. The shape and size of these pores allow only specific reactant molecules to enter and only specific product molecules to leave. This ensures that only certain reactions occur, making them highly efficient for specific processes.
In simple words: Zeolites are like tiny sponges with specific holes. They are used to speed up chemical reactions, especially in making fuel. They work by letting only certain molecules go into their holes to react, which makes them very good at making specific products.

🎯 Exam Tip: Focus on "microporous aluminosilicates," "acidic/basic catalysis," and especially "shape selectivity" as key features of zeolites. Mentioning their use in petrochemicals provides a good real-world context.

Question 16. Give three uses of emulsions.
Answer: Emulsions have many practical applications:
1. **Cleansing Action of Soap:** The way soap cleans is due to its emulsifying action. Soap helps to break down oily dirt into tiny droplets that can be dispersed in water and washed away.
2. **Cosmetics and Pharmaceuticals:** Emulsions are used to make various products like vanishing creams, lotions, and many pharmaceutical preparations. These creams allow different ingredients (like oil and water) to mix smoothly.
3. **Nutritional Supplements:** Emulsions are also used in things like cod liver oil. This helps in delivering important nutrients that might not mix well with other liquids.
In simple words: Emulsions help soap clean things, they are used to make creams and medicines smooth, and they help mix oils like cod liver oil so we can take them easily.

🎯 Exam Tip: When listing uses, pick diverse examples like cleaning, cosmetics, and medicine to show a broad understanding of emulsion applications.

Question 17. Why does the bleeding stop by rubbing moist alum?
Answer: Bleeding stops when moist alum is rubbed on an injured area because blood is a colloidal solution. When alum, which contains \( \text{Al}^{3+} \) ions, comes into contact with blood, these ions cause the coagulation of blood. Coagulation means the blood particles clump together and solidify. This forms a clot that seals the wound and prevents further bleeding. Alum is often used as an antiseptic and styptic agent due to this property.
In simple words: Blood is like a liquid mixture with tiny particles. Alum makes these particles stick together and form a solid, which helps stop the bleeding.

🎯 Exam Tip: The key terms here are "colloidal sol," "coagulation," and the role of \( \text{Al}^{3+} \) ions in neutralizing the charge on blood particles, leading to clotting.

Question 18. Why is desorption important for a substance to act as good catalyst?
Answer: Desorption is a crucial step for a substance to be an effective catalyst. Here's why:
1. **Creating Space:** After a chemical reaction happens on the catalyst's surface, the newly formed product molecules must detach from the surface (desorb). This desorption creates empty sites on the catalyst surface. These empty sites are then available for new reactant molecules to adsorb and start another reaction cycle.
2. **Continuous Reaction:** If the product molecules did not desorb, they would stay stuck to the catalyst surface. This would block the active sites, preventing fresh reactant molecules from attaching. As a result, the catalytic process would stop or slow down significantly. So, desorption ensures a continuous and efficient catalytic reaction.
In simple words: For a catalyst to work well again and again, the new chemicals it helps make must leave its surface. If they stay, new chemicals can't stick, and the catalyst stops working.

🎯 Exam Tip: Emphasize that desorption makes active sites available for fresh reactants, ensuring the continuous cycling and efficiency of the catalyst. It's about 'clearing the surface' for the next reaction.

Question 19. Comment on the statement: Colloid is not a substance but it is a state of the substance.
Answer: The statement "Colloid is not a substance but it is a state of the substance" is entirely true. This is because the same substance can exist as a colloid under certain conditions and as a non-colloidal form (crystalloid) under different conditions. For example, sodium chloride (\( \text{NaCl} \)) behaves as a crystalloid when dissolved in water, forming a true solution. However, if \( \text{NaCl} \) is dissolved in benzene, it can form a colloidal solution. Similarly, a soap solution behaves as a colloid. The classification depends on the size of the particles dispersed in a medium. If the particle diameter falls within the range of 1 nanometer (nm) to 100 nm, it is considered a colloidal state. Therefore, "colloid" describes a specific physical state of matter based on particle size, not a unique type of substance itself.
In simple words: Yes, it's true! A substance can be a colloid sometimes and not other times, depending on how big its tiny pieces are. If the pieces are between 1 to 100 nanometers, it acts like a colloid. So, it's a way the substance behaves, not a new kind of substance.

🎯 Exam Tip: Highlight the particle size range (1-100 nm) as the defining characteristic of the colloidal state. Use examples like \( \text{NaCl} \) in different solvents to illustrate that the same substance can exist in both colloidal and non-colloidal states.

Question 20. Explain any one method for coagulation.
Answer: Coagulation is the process where colloidal particles clump together and settle down, leading to the precipitation of the sol. Here's an explanation of one method:
**Addition of Electrolytes:** Colloidal particles carry an electric charge (either positive or negative). They remain stable because these like charges repel each other, preventing them from clumping. When an electrolyte (a substance that forms ions in solution) is added, the ions with an opposite charge to the colloidal particles are attracted to them. These oppositely charged ions neutralize the charge on the colloidal particles, reducing the repulsion between them. As a result, the particles can come closer, collide, and aggregate, eventually settling down. For example, a negatively charged sol will be coagulated by positive ions. The greater the charge (valency) of the flocculating ion, the higher its power to cause precipitation (Hardy-Schulze rule). For instance, for negatively charged sols, the precipitation power of cations increases in the order: \( \text{Na}^+ < \text{Ba}^{2+} < \text{Al}^{3+} \). Similarly, for positively charged sols, the power of anions increases as: \( \text{Cl}^- < \text{SO}_4^{2-} < [\text{Fe(CN)}_6]^{3-} \).
The minimum concentration of an electrolyte (in millimoles per liter) required to cause precipitation of a sol in 2 hours is called its flocculation value. A smaller flocculation value indicates a greater coagulating power.
In simple words: To make tiny particles in a liquid clump and settle (coagulate), you can add a salt. The salt's opposite-charged parts cancel out the charge on the tiny particles, making them stick together and fall to the bottom. Stronger-charged salt parts work better.

🎯 Exam Tip: When explaining coagulation by electrolytes, mention the neutralization of charge and the Hardy-Schulze rule (valency of the ion is crucial). Clearly state that a smaller flocculation value means greater coagulating power.

Question 21. Write a note on electroosmosis.
Answer: Electro-osmosis is a phenomenon where the dispersion medium (the liquid part) of a colloidal system moves under the influence of an electric field. This happens when the colloidal particles themselves are prevented from moving. Colloidal solutions are electrically neutral overall, but the dispersed particles carry a charge, and the surrounding medium carries an equal and opposite charge. So, when an electric potential is applied, if the particles cannot move (e.g., due to a barrier), the liquid medium will move in the opposite direction. This movement of the dispersion medium relative to the stationary dispersed phase under an electric field is called electro-osmosis. This process is useful in many industrial applications for separating components in colloidal systems.
In simple words: Electro-osmosis is when the liquid part of a colloid moves because of electricity, while the tiny particles stay still. This happens because the liquid and particles have opposite electrical charges.

🎯 Exam Tip: Distinguish electro-osmosis from electrophoresis. In electro-osmosis, the *dispersion medium* moves, while in electrophoresis, the *dispersed particles* move, both under an electric field.

Question 22. Write a note on catalytic poison.
Answer: A catalytic poison is a substance that reduces or completely destroys the activity of a catalyst. These substances interfere with the catalyst's ability to speed up a reaction. They often do this by strongly adsorbing onto the active sites of the catalyst, blocking them from interacting with the reactant molecules. This means the catalyst can no longer perform its function effectively. For example, in the production of sulfur trioxide (\( \text{SO}_3 \)) from sulfur dioxide (\( \text{SO}_2 \)) and oxygen (\( \text{O}_2 \)) using a platinum (\( \text{Pt} \)) catalyst:
\[ 2\text{SO}_{2}\text{(g)} + \text{O}_{2}\text{(g)} \xrightarrow{\text{Pt catalyst}} 2\text{SO}_{3}\text{(g)} \]
Arsenic trioxide (\( \text{As}_2\text{O}_3 \)) acts as a catalytic poison. It attaches to the platinum surface, blocking its active sites and causing the catalyst to lose its activity. This unwanted effect is crucial in industrial processes, as even small amounts of poison can ruin a catalyst batch.
In simple words: A catalytic poison is something that stops a catalyst from working. It sticks to the catalyst's special spots, so the catalyst can't help reactions anymore.

🎯 Exam Tip: Define catalytic poison clearly and explain how it acts (blocking active sites). Use the example of \( \text{As}_2\text{O}_3 \) poisoning a platinum catalyst in \( \text{SO}_3 \) production.

Question 23. Explain intermediate compound formation theory of catalysis with an example.
Answer: The intermediate compound formation theory explains how catalysts work, especially in homogeneous catalysis. According to this theory, a catalyst first combines with one or more reactant molecules to form an unstable intermediate compound. This intermediate compound then reacts with another reactant or breaks down to produce the final products, regenerating the original catalyst in the process. The formation and decomposition of this intermediate compound have lower activation energies than the uncatalyzed reaction, which speeds up the overall reaction. The catalyst is not used up in the reaction.
Consider the general reactions:
1. \( \text{A} + \text{B} \rightarrow \text{AB} \) (Uncatalyzed reaction)
If \( \text{C} \) is the catalyst, the mechanism involves:
2. \( \text{A} + \text{C} \rightarrow \text{AC} \) (Intermediate compound formation)
3. \( \text{AC} + \text{B} \rightarrow \text{AB} + \text{C} \) (Intermediate reacts to form product and regenerate catalyst)
The activation energies for steps (2) and (3) are lowered compared to step (1), thus increasing the reaction rate. This theory describes two key aspects:
1. **Specificity:** It helps explain why a catalyst is specific to certain reactions.
2. **Rate Increase:** It explains how increasing the concentration of a catalyst can increase the reaction rate.
**Example: Friedel-Crafts Reaction**
In this reaction, aluminum chloride (\( \text{AlCl}_3 \)) acts as a catalyst. For example, in the alkylation of benzene:
\[ \text{C}_6\text{H}_6 + \text{CH}_3\text{Cl} \xrightarrow{\text{Anhydrous AlCl}_3} \text{C}_6\text{H}_5\text{CH}_3 + \text{HCl} \]
The action of the catalyst is explained as follows:
The methyl chloride (\( \text{CH}_3\text{Cl} \)) first reacts with \( \text{AlCl}_3 \) to form an intermediate carbocation:
\[ \text{CH}_3\text{Cl} + \text{AlCl}_3 \rightarrow [\text{CH}_3]^+ [\text{AlCl}_4]^- \]
This intermediate carbocation then reacts with benzene (\( \text{C}_6\text{H}_6 \)):
\[ \text{C}_6\text{H}_6 + [\text{CH}_3]^+ [\text{AlCl}_4]^- \rightarrow \text{C}_6\text{H}_5\text{CH}_3 + \text{AlCl}_3 + \text{HCl} \]
The catalyst \( \text{AlCl}_3 \) is regenerated in the process. This theory helps explain the faster rate by creating a new reaction pathway.
**Limitations:**
1. This theory doesn't fully explain the role of catalytic poisons and promoters, which can stop or enhance catalyst activity.
2. It also cannot completely explain how heterogeneous catalyzed reactions work, where the catalyst and reactants are in different phases.
In simple words: This theory says that a catalyst works by first joining with one starting chemical to make a temporary new chemical. This new temporary chemical then quickly reacts with other starting chemicals to make the final product, and the catalyst is set free again. It's like a shortcut that uses less energy. However, it doesn't explain everything, like why some things stop catalysts from working or how catalysts work when they are in a different state from the reacting chemicals.

🎯 Exam Tip: Clearly state that the catalyst forms an unstable intermediate with lower activation energy. Provide the general two-step mechanism (A+C -> AC; AC+B -> AB+C) and explain how the catalyst is regenerated at the end. Also, remember its limitations, especially regarding catalytic poisons and heterogeneous catalysis.

Question 24. What is the difference between homogeneous and heterogeneous catalysis?
Answer: The difference between homogeneous and heterogeneous catalysis depends on the physical state of the reactants, products, and the catalyst.
**Homogeneous Catalysis:**
1. In this type of catalysis, the reactants, products, and the catalyst are all in the same physical phase (e.g., all gases or all liquids).
2. **Example:** The oxidation of sulfur dioxide (\( \text{SO}_2 \)) to sulfur trioxide (\( \text{SO}_3 \)) using nitric oxide (\( \text{NO} \)) as a catalyst in the lead chamber process:
\[ 2\text{SO}_{2}\text{(g)} + \text{O}_{2}\text{(g)} \xrightarrow{\text{NO(g)}} 2\text{SO}_{3}\text{(g)} \]
Here, \( \text{SO}_2 \), \( \text{O}_2 \), \( \text{NO} \), and \( \text{SO}_3 \) are all in the gaseous phase. This type of catalysis is often explained by the intermediate compound formation theory.
**Heterogeneous Catalysis:**
1. In this type, the catalyst is in a different physical phase than the reactants and products (e.g., a solid catalyst with gaseous reactants).
2. **Example:** The oxidation of sulfur dioxide (\( \text{SO}_2 \)) to sulfur trioxide (\( \text{SO}_3 \)) using platinum (\( \text{Pt} \)) as a catalyst in the contact process:
\[ 2\text{SO}_{2}\text{(g)} + \text{O}_{2}\text{(g)} \xrightarrow{\text{Pt(s)}} 2\text{SO}_{3}\text{(g)} \]
Here, \( \text{SO}_2 \) and \( \text{O}_2 \) are gases, while \( \text{Pt} \) is a solid. Heterogeneous catalysis is typically explained by the adsorption theory, where reactants adsorb onto the catalyst surface.
In simple words: In homogeneous catalysis, everything (starting chemicals, catalyst, and end products) is in the same physical state, like all liquids or all gases. In heterogeneous catalysis, the catalyst is in a different state, like a solid helping gases react.

🎯 Exam Tip: The crucial distinction is the phase of the catalyst relative to the reactants/products. Provide a clear example for each type, including the phases of all components.

Question 25. Describe adsorption theory of catalysis.
Answer: The adsorption theory (also known as the contact catalysis theory) explains the mechanism of heterogeneous catalysis, where the catalyst is in a different phase from the reactants. Langmuir was one of the scientists who helped explain this theory. This theory suggests that the reactant molecules are attracted to and stick to the surface of the solid catalyst, where the reaction then takes place. The process involves several steps:
1. **Diffusion of Reactants:** Reactant molecules from the bulk phase (e.g., gas or liquid) first move and spread out towards the surface of the catalyst.
2. **Adsorption of Reactants:** The reactant molecules then attach themselves to the active sites on the catalyst's surface. This process is called adsorption.
3. **Formation of Activated Complex:** Once adsorbed, the reactant molecules become activated and interact with each other to form an unstable intermediate, also called an activated complex. This complex helps to lower the activation energy for the reaction.
4. **Decomposition of Activated Complex:** The activated complex then breaks down, forming the product molecules on the catalyst's surface.
5. **Desorption of Products:** The product molecules detach from the catalyst surface (desorb) and move away into the bulk phase. This frees up the active sites on the catalyst for new reactant molecules to adsorb. The diagram showing ethylene adsorption on a nickel surface illustrates this process, where the \( \text{Ni} \) surface breaks \( \pi \) bonds in ethylene to facilitate its reaction.
In simple words: This theory says that when a catalyst is solid and the chemicals are gas, the gas chemicals first stick to the solid catalyst. They react on its surface, make new products, and then these products leave the surface, making space for more chemicals to react.

🎯 Exam Tip: Clearly outline the five steps: diffusion, adsorption, activated complex formation, decomposition, and desorption. Emphasize the role of active sites on the catalyst surface and the regeneration of these sites by product desorption.

Part - II - Additional Questions

I. Choose the Correct Answer

Question 1. Adsorption is a
(a) Bulk phenomenon
(b) Surface phenomenon
(c) Both (a) and (b)
(d) None of the options
Answer: (b) Surface phenomenon
In simple words: Adsorption happens only on the outside layer of a substance, not throughout its entire body.

🎯 Exam Tip: Always remember that adsorption involves concentration on the surface, making it a surface phenomenon, unlike absorption which is a bulk phenomenon.

Question 2. Absorption is a
(a) Bulk phenomenon
(b) Surface phenomenon
(c) Both (a) and (b)
(d) None of the options
Answer: (a) Bulk phenomenon
In simple words: Absorption means a substance goes inside and spreads all through another substance, not just on the surface.

🎯 Exam Tip: Distinguish absorption (material enters the bulk) from adsorption (material stays on the surface) as a common point of confusion.

Question 3. Which among the following is an adsorbent?
(a) \( \text{N}_2 \)
(b) \( \text{SO}_2 \)
(c) \( \text{Ni} \)
(d) \( \text{H}_2 \)
Answer: (c) Ni
In simple words: An adsorbent is the material that collects other substances on its surface. Out of the options, Nickel (\( \text{Ni} \)) is a solid metal that can do this.

🎯 Exam Tip: An adsorbent is the surface on which adsorption occurs, typically a solid with a large surface area, while adsorbate is the substance that gets adsorbed (usually a gas or liquid).

Question 4. In adsorption, if the concentration of a substance in the interface is high, then it is called?
(a) Desorption
(b) Positive adsorption
(c) Negative adsorption
(d) Absorption
Answer: (b) Positive adsorption
In simple words: If a lot of a substance gathers at the surface, it's called positive adsorption.

🎯 Exam Tip: Positive adsorption means the concentration of adsorbate is higher at the interface than in the bulk, while negative adsorption means it's lower.

Question 5. Adsorption process is
(a) Spontaneous
(b) Non-spontaneous
(c) Slow
(d) Bulk phenomenon
Answer: (a) Spontaneous
In simple words: Adsorption happens naturally on its own without needing extra effort or energy input.

🎯 Exam Tip: A spontaneous process is characterized by a decrease in Gibbs free energy (\( \Delta G < 0 \)). Adsorption is spontaneous because it reduces surface energy and increases entropy for the bulk system.

Question 6. Adsorption is always accompanied by
(a) Increase in entropy
(b) Increase in free energy
(c) Decrease in free energy
(d) Increase in surface energy
Answer: (c) Decrease in free energy
In simple words: When adsorption happens, the total useful energy in the system goes down, making the process favorable.

🎯 Exam Tip: For a process to be spontaneous (like adsorption), the Gibbs free energy (\( \Delta G \)) must decrease (\( \Delta G < 0 \)). This is linked to the decrease in enthalpy and an overall increase in system stability.

Question 7. The force of attraction exist between adsorbent and adsorbate in physical adsorption is
(a) Vanderwaal's force
(b) Dipole-dipole interaction
(c) Dispersion forces
(d) All the options
Answer: (d) All the options
In simple words: In physical adsorption, the weak forces that hold the two substances together include van der Waals forces, which cover different types like dipole-dipole interactions and dispersion forces.

🎯 Exam Tip: Physical adsorption (physisorption) is characterized by weak, non-specific intermolecular forces, which include all types of van der Waals forces (dispersion, dipole-dipole, and dipole-induced dipole interactions).

Question 8. Total amount of the gas adsorbed increases as the ............ of the adsorbent increases.
(a) Volume
(b) Density
(c) Surface area
(d) Surface tension
Answer: (c) Surface area
In simple words: The more surface a substance has, the more gas can stick to it.

🎯 Exam Tip: Surface area is a primary factor influencing adsorption capacity; a larger surface provides more active sites for adsorbate molecules.

Question 9. The critical temperature of the gas which is readily adsorbed is
(a) lower
(b) higher
(c) zero
(d) None of the options
Answer: (b) higher
In simple words: Gases that can be turned into liquid more easily (meaning they have a higher critical temperature) are also more easily adsorbed onto a surface.

🎯 Exam Tip: Gases with higher critical temperatures are more easily liquefiable and have stronger intermolecular forces, making them more readily adsorbed on solid surfaces.

Question 10. Which among the following gas is adsorbed slowly?
(a) \( \text{SO}_2 \)
(b) \( \text{NH}_3 \)
(c) \( \text{N}_2 \)
(d) \( \text{CO}_2 \)
Answer: (c) N_2
In simple words: Nitrogen gas is adsorbed slowly because it is harder to turn into a liquid, meaning it has weak attractive forces.

🎯 Exam Tip: Gases with lower critical temperatures are less easily liquefiable and have weaker intermolecular forces, leading to slower and less extensive adsorption. Nitrogen (\( \text{N}_2 \)) has a very low critical temperature compared to \( \text{SO}_2 \), \( \text{NH}_3 \), and \( \text{CO}_2 \).

Question 11. The process of adsorption is
(a) Exothermic
(b) Endothermic
(c) Both (a) and (b)
(d) None of the options
Answer: (a) Exothermic
In simple words: Adsorption usually releases heat, which means it's an exothermic process.

🎯 Exam Tip: The formation of bonds between adsorbate and adsorbent releases energy, making the overall adsorption process typically exothermic. This is why increasing temperature generally decreases adsorption.

Question 12. Multi molecular layers are formed in
(a) Absorption
(b) Physisorption
(c) Chemisorption
(d) None of the options
Answer: (b) Physisorption
In simple words: In physisorption, many layers of gas can stick to the surface, one on top of another.

🎯 Exam Tip: Physisorption is characterized by the formation of multilayer adsorption due to weak van der Waals forces, whereas chemisorption is typically monolayer due to strong chemical bonding.

Question 14. In adsorption isobar the amount of adsorption is plotted against
(a) Pressure
(b) Temperature
(c) Volume
(d) Mass
Answer: (b) Temperature
In simple words: An adsorption isobar shows how much gas is adsorbed on a solid surface when the temperature changes, but the pressure stays the same. It helps us see the effect of heat.

🎯 Exam Tip: Remember that "isobar" refers to constant pressure, just as "isotherm" refers to constant temperature.

Question 15. In physical adsorption isobar x /m, .................................... with increase in temperature.
(a) Increases
(b) Decreases
(c) First increases then decreases
(d) Does not change
Answer: (b) Decreases
In simple words: When you warm up a physically adsorbed gas, it tends to leave the surface of the solid. This is because the gas particles get more energy and break away.

🎯 Exam Tip: Physisorption is an exothermic process, meaning it releases heat. According to Le Chatelier's principle, increasing temperature will shift the equilibrium towards desorption (removing gas from the surface).

Question 16. In chemisorption isobar x /m .................................... with increase in temperature.
(a) Increases
(b) Decreases
(c) First increases then decreases
(d) Does not change
Answer: (c) First increases then decreases
In simple words: For chemical adsorption, increasing the temperature first helps the gas stick better to the surface, but if it gets too hot, the gas starts to come off. It is like needing a little warmth to cook something, but too much will burn it.

🎯 Exam Tip: Chemisorption often requires an activation energy, which explains the initial increase with temperature, but being exothermic, high temperatures then favor desorption.

Question 17. Which of the following is not an equation for Freundlich isotherm?
(a) \( \frac{x}{m} = kP^n \)
(b) \( \frac{x}{m} = kC^n \)
(c) \( \log \frac{x}{m} = \log k + \frac{1}{n}\log P \)
(d) \( \log \frac{x}{m} = \log k - \frac{1}{n}\log P \)
Answer: (d) \( \log \frac{x}{m} = \log k - \frac{1}{n}\log P \)
In simple words: The Freundlich isotherm equation shows how much gas sticks to a solid at a certain temperature. When you write it using "log" (logarithm), the sign before \( \frac{1}{n}\log P \) should be plus, not minus.

🎯 Exam Tip: The Freundlich isotherm expresses adsorption as \( \frac{x}{m} = kP^{1/n} \), which becomes \( \log \frac{x}{m} = \log k + \frac{1}{n}\log P \) in its logarithmic form.

Question 18. Sugar prepared from molasses is decolourised by adding.
(a) Silica gel
(b) Permutit
(c) Animal Charcoal
(d) Activated charcoal
Answer: (c) Animal Charcoal
In simple words: To make sugar white, we use animal charcoal. It soaks up the colored stuff from the molasses, which is the raw sugar syrup. This makes the sugar clean and white.

🎯 Exam Tip: Animal charcoal is a powerful adsorbent, commonly used in industries like sugar refining to remove impurities and color.

Question 19. Which of the following is not an application of adsorption?
(a) Heterogeneous catalysis
(b) Gas masks
(c) Froth floatation process
(d) Softening of water by boiling
Answer: (d) Softening of water by boiling
In simple words: Adsorption is used in many ways, like making catalysts work, in gas masks, and for separating minerals. Boiling water makes it soft by changing hard minerals into solids that sink, but this is not adsorption.

🎯 Exam Tip: Boiling removes temporary hardness by converting soluble bicarbonates into insoluble carbonates, which then precipitate, a process distinct from adsorption.

Question 20. The change of W/O emulsion into O/W emulsion is called ....................................
(a) Coagulation
(b) Emulsification
(c) Decomposition
(d) Inversion of phase
Answer: (d) Inversion of phase
In simple words: When an emulsion changes from being water mixed in oil to oil mixed in water, it is called phase inversion. It means the roles of the two liquids switch.

🎯 Exam Tip: Phase inversion indicates a change in the continuous phase, often triggered by changing the emulsifier or the ratio of the components.

Question 21. \( 2SO_2 + O_2 + [NO] \rightarrow 2SO_3 + [NO] \) is an example for
(a) Positive catalysis
(b) Negative catalysis
(c) Homogeneous catalysis
(d) Both (a) and (c)
Answer: (d) Both (a) and (c)
In simple words: In this reaction, NO speeds up the making of \( SO_3 \). Since NO is in the same gas phase as the other chemicals, it is a homogeneous catalyst. Because it speeds up the reaction, it is also a positive catalyst.

🎯 Exam Tip: Homogeneous catalysis occurs when the catalyst and reactants are in the same physical state (phase).

Question 22. Which is not a heterogeneous catalysis?
(a) Contact process
(b) Haber's process
(c) Ester hydrolysis
(d) Ostwald's process
Answer: (c) Ester hydrolysis
In simple words: In most chemical reactions, if the catalyst is in a different state (like a solid helping gases), it is called heterogeneous catalysis. Ester hydrolysis can happen when both the ester and the acid or base catalyst are dissolved in water, meaning they are all in the same liquid state.

🎯 Exam Tip: Heterogeneous catalysis is recognized when the catalyst and reactants are in different phases, such as a solid catalyst facilitating a gas-phase reaction.

Question 23. Intermediate compound formation theory explains.
(a) Homogeneous catalysis
(b) Heterogeneous catalysis
(c) Autocatalysis
(d) Negative catalysis
Answer: (a) Homogeneous catalysis
In simple words: This theory says that a catalyst works by first forming a new, temporary chemical with one of the reacting substances. Then, this temporary chemical reacts with the second substance, makes the final product, and also frees up the catalyst again. This explanation works well for reactions where everything is in the same state, like all liquids or all gases.

🎯 Exam Tip: The intermediate compound formation theory describes how a catalyst actively participates in a reaction by forming a short-lived intermediate, which then breaks down to regenerate the catalyst and produce the product.

Question 24. In intermediate compound formation, the intermediate complex formed has
(a) More activation energy than uncatalysed complex
(b) Less activation energy than uncatalysed complex
(c) Less kinetic energy than the reactants
(d) Less kinetic energy than the products
Answer: (b) Less activation energy than uncatalysed complex
In simple words: When a catalyst helps a reaction, it creates a new pathway for the reaction to happen. This new pathway needs less energy to start than the old way, making the reaction go faster. Think of it as finding an easier path over a hill.

🎯 Exam Tip: Catalysts speed up reactions by lowering the activation energy, which is the minimum energy required for reactants to turn into products.

Question 25. Adsorption theory explains
(a) Homogeneous catalysis
(b) Heterogeneous catalysis
(d) Negative catalysis
Answer: (b) Heterogeneous catalysis
In simple words: The adsorption theory helps explain how catalysts work when they are in a different physical state than the reacting chemicals. For example, if a solid surface helps gases react, the gas molecules first stick to the surface (adsorb) and then react there.

🎯 Exam Tip: Adsorption theory details how reactant molecules adhere to the catalyst surface, weakening their bonds and facilitating product formation, which is key for heterogeneous reactions.

Question 26. The catalytic activity of a catalyst is increased by a promoter by
(a) Increasing the number of active centres
(b) Decreasing the number of active centres.
(c) Blocking the number of active centres
(d) Desorbing the active centres
Answer: (a) Increasing the number of active centres
In simple words: A promoter is like a helper for a catalyst. It makes the catalyst work better by creating more special spots on the catalyst's surface where reactions can happen. This helps more chemicals react.

🎯 Exam Tip: Promoters enhance catalytic activity, often by modifying the electronic structure or increasing the surface area and active sites of the catalyst.

Question 27. Enzymes are often present as
(a) Crystalloids
(b) Suspension
(c) Colloids
(d) True solutions
Answer: (c) Colloids
In simple words: Enzymes are large protein molecules that act as catalysts in living things. They are usually found in a colloidal state, meaning they are dispersed as very tiny particles in a liquid, but not dissolved like sugar in water.

🎯 Exam Tip: Colloids have particle sizes between 1 nm and 1000 nm, allowing them to remain dispersed without settling, which is ideal for biological catalysts like enzymes.

Question 28. In the conversion of 1 - chloro octane into 1 - cyano octane, tetra alkyl ammonium cation acts as a
(a) Enzyme catalyst
(b) Phase transfer catalyst
(c) Zeolite catalyst
Answer: (b) Phase transfer catalyst
In simple words: When two chemicals that do not mix well need to react, a phase transfer catalyst helps them. It carries one chemical from its own liquid layer to the other liquid layer so they can meet and react.

🎯 Exam Tip: Phase transfer catalysts are particularly useful in facilitating reactions between immiscible phases, bridging the gap between them to enhance reaction rates.

Question 29. Which of the following is incorrect
(a) Enzymes can be inhibited (poisoned)
(b) Catalytic activity of enzymes is decreased by coenzymes.
(c) Enzyme catalysis is highly specific in nature
(d) the rate of Enzyme catalysed reactions varies with the pH of the system.
Answer: (b) Catalytic activity of enzymes is decreased by coenzymes.
In simple words: Coenzymes actually help enzymes work better; they do not decrease their activity. Enzymes are very specific, can be stopped by poisons, and work best at a certain pH level.

🎯 Exam Tip: Coenzymes are organic non-protein molecules that bind to enzymes and are essential for their catalytic activity, meaning they are helpers, not inhibitors.

Question 30. Nano catalysts can act as
(a) Homogeneous catalysts
(b) Heterogeneous catalysts
(c) Phase transfer catalysts
(d) Both (a) and (b)
Answer: (d) Both (a) and (b)
In simple words: Nano catalysts are tiny bits of material that can act as catalysts. Because they are so small, they can sometimes mix fully with the reacting chemicals (homogeneous) or stay separate like a solid powder (heterogeneous). This makes them very versatile.

🎯 Exam Tip: The unique properties of nanoparticles, including their high surface area, allow them to exhibit catalytic behavior in both homogeneous and heterogeneous systems.

Question 31. Size of colloidal particle is
(a) 1 - 200 Å
(b) 1 - 200 nm
(c) 1 - 200 pm
(d) 1 - 200 pm
Answer: (b) 1 - 200 nm
In simple words: Colloidal particles are much smaller than what you can see with your eyes, but bigger than individual molecules. Their size is usually between 1 and 200 nanometers. This special size gives them unique properties.

🎯 Exam Tip: The size range of colloidal particles (1-1000 nm, or commonly 1-200 nm as an approximation) is crucial for their unique properties, such as Tyndall effect and Brownian motion.

Question 32. In hydrosols the dispersion medium is
(a) Benzene
(b) Alcohol
(c) Water
(d) Ether
Answer: (c) Water
In simple words: A hydrosol is a type of colloid where tiny particles are spread out in water. So, water is the liquid that holds everything. The "hydro" part of the name means water.

🎯 Exam Tip: The "sol" suffix typically denotes a colloidal dispersion, and prefixes like "hydro-", "alco-", or "benzi-" specify the dispersion medium (water, alcohol, or benzene, respectively).

Question 33. In lyophillic colloids which is true?
(a) Definite attractive force exists between the dispersion medium and dispersed phase
(b) More stable
(c) Reversible sols
(d) All the options
Answer: (d) All the options
In simple words: Lyophilic colloids love their liquid environment. This means they are very stable, easy to put back together if they separate, and have a strong pull between the particles and the liquid around them.

🎯 Exam Tip: Lyophilic colloids are characterized by a strong affinity between the dispersed phase and the dispersion medium, contributing to their stability and reversibility.

Question 34. In lyophobic colloids which is not true?
(a) No attractive force exists between the dispersion medium and dispersed phase
(b) Less stable
(c) Can be produced again
(d) Precipitated readily
Answer: (c) Can be produced again
In simple words: Lyophobic colloids do not like their liquid environment much. They are unstable and easily separate. Once they separate, it is hard to make them come back together easily.

🎯 Exam Tip: Lyophobic colloids are irreversible; once coagulated or precipitated, they cannot be easily reformed by simply remixing the components, unlike lyophilic colloids.

Question 35. What among the following is a liquid aerosol?
(a) Smoke
(b) Fog
(c) Shaving cream
(d) Froth
Answer: (b) Fog
In simple words: A liquid aerosol is like a cloud of tiny liquid drops floating in a gas. Fog is a good example because it is made of tiny water droplets hanging in the air.

🎯 Exam Tip: Aerosols are colloids where fine solid particles or liquid droplets are dispersed in a gas. A liquid aerosol specifically has liquid droplets in a gas.

Question 36. Which one of the following is negatively charged colloid?
(a) arsenic sulphide
(b) Ferric hydroxide
(c) Haemoglobin
(d) Basic dyes
Answer: (a) arsenic sulphide
In simple words: Some colloids have a negative charge, and others have a positive charge. Arsenic sulphide colloid particles carry a negative charge. This charge helps them stay spread out and not clump together.

🎯 Exam Tip: The charge on colloidal particles is important for their stability. Negatively charged sols typically include metal sulfides (like \( As_2S_3 \)), metals, and acid dyes.

Question 37. Butter is a colloid of
(a) Solid, gas
(b) Liquid, solid
(c) Solid, liquid
(d) Gas, solid
Answer: (b) Liquid, solid
In simple words: Butter is a colloid where tiny drops of liquid are spread throughout a solid. It is like having water mixed into a fatty solid. This mix makes butter spreadable and creamy.

🎯 Exam Tip: Butter is a water-in-oil emulsion, which then solidifies, making it a dispersion of liquid (water) in a solid (fat).

Question 38. Dispersed phase and the dispersion medium are respectively
(a) Solid in liquid
(b) Liquid in solid
(c) Liquid in liquid
(d) Liquid in gas
Answer: (b) Liquid in solid
In simple words: This question seems incomplete without referring to a specific colloid example. However, if we assume it refers to the prior discussion of butter, butter is a system where liquid (dispersed phase) is spread within a solid (dispersion medium).

🎯 Exam Tip: For colloid classification, the dispersed phase is the substance scattered in the medium, and the dispersion medium is the substance where it is scattered.

Question 39. Colloidal graphite can be prepared by
(a) Peptisation
(b) Mechanical dispersion
(c) Ultrasonic dispersion
(d) Double decomposition
Answer: (b) Mechanical dispersion
In simple words: To make colloidal graphite, you break down big pieces of graphite into very tiny particles. This is usually done by grinding or crushing them very finely, often in a special machine. This is a physical way to make colloids.

🎯 Exam Tip: Mechanical dispersion involves using high-speed grinders or colloid mills to break down larger particles into colloidal size, especially effective for solid substances.

Question 40. Electro dispersion method is used to prepare the colloidal solution of
(a) Copper
(b) Silver
(c) Gold
(d) All the options
Answer: (d) All the options
In simple words: The electro-dispersion method, also called Bredig's arc method, is a way to make colloids of metals. It works for metals like gold, silver, and copper. This method uses electricity to make tiny metal particles.

🎯 Exam Tip: Bredig's arc method is suitable for preparing sols of noble metals by creating an electric arc between metal electrodes immersed in a dispersion medium.

Question 40. Arsenic sulphide sol is prepared by the reaction. \( AS_2O_3 + 3H_2S \rightarrow As_2S_3 + 3H_2O \). This method is known as
(b) Double decomposition
Answer: (b) Double decomposition
In simple words: In this chemical reaction, two compounds exchange parts to form new compounds. Here, arsenic oxide and hydrogen sulfide react to make arsenic sulfide colloid and water. It is a common way to form some colloids.

🎯 Exam Tip: Double decomposition reactions involve the exchange of ions between two compounds, often leading to the formation of a precipitate or a colloidal sol.

Question 42. Conversion of a colloid into a precipitate is known as
(a) Peptisation
(b) Dialysis
(c) Coagulation
(d) Electrophoresis
Answer: (c) Coagulation
In simple words: When tiny colloid particles clump together and settle down as a solid, it is called coagulation. This process changes a stable colloid into a solid mass. It is like milk turning into cheese.

🎯 Exam Tip: Coagulation (or flocculation) is the process by which colloidal particles aggregate and precipitate out of dispersion, often initiated by adding an electrolyte.

Question 43. Conversion of a precipitate into a colloid is known as
(a) Peptisation
(b) Dialysis
(c) Coagulation
(d) Electrophoresis
Answer: (a) Peptisation
In simple words: Peptisation is the process where a fresh solid (precipitate) is changed back into a colloid. This happens when a small amount of a special chemical is added, which helps the solid break up into tiny, stable particles.

🎯 Exam Tip: Peptisation is essentially the reverse of coagulation, where a precipitate is converted into a colloidal sol by the addition of an electrolyte (peptizing agent).

Question 43. The removal of electrolytic impurities from a colloidal solution is known as
(a) Peptisation
(b) Dialysis
(c) Coagulation
(d) Electrophoresis
Answer: (b) Dialysis
In simple words: Dialysis is a way to clean colloids by removing small unwanted particles, like salts. It uses a special membrane that lets the small impurities pass through but holds back the larger colloid particles. This cleans the colloid.

🎯 Exam Tip: Dialysis separates crystalloids from colloids based on differences in particle size, using a semipermeable membrane that allows only smaller solute particles to diffuse through.

Question 44. The movement of dispersed phase under the influence of electric current is known as
(a) Electro osmosis
(b) Electrophoresis
(c) Dialysis
(d) Electrophoresis
Answer: (b) Electrophoresis
In simple words: When small colloid particles start moving in a liquid because of an electric current, this movement is called electrophoresis. It shows that colloid particles have an electric charge.

🎯 Exam Tip: Electrophoresis is a phenomenon where charged colloidal particles migrate towards the electrode of opposite charge under the influence of an electric field.

Question 45. The movement of dispersed phase under the influence of electric current is known as
(a) Electro osmosis
(b) Electrophoresis
(c) Electrodialysis
(d) Ultra filteration
Answer: (b) Electrophoresis
In simple words: When the tiny particles spread out in a colloid move because of electricity, it is called electrophoresis. This happens because the particles have an electric charge. This movement helps us understand how stable a colloid is.

🎯 Exam Tip: Electrophoresis is crucial for determining the charge on colloidal particles and for various separation techniques in biochemistry.

Question 46. The movement of dispersion medium under the influence of electric current is known as
(a) Electro osmosis
(b) Electrophoresis
(c) Electrodialysis
(d) Ultra filteration
Answer: (a) Electro osmosis
In simple words: If the tiny particles in a colloid are stopped from moving, but the liquid they are in starts to move because of an electric current, that is called electro-osmosis. It is like the liquid itself is being pushed by the electricity.

🎯 Exam Tip: Electro-osmosis is the movement of the dispersion medium relative to a stationary charged surface under an applied electric field.

Question 47. In ultra filtration, ultrafilters are made by using
(a) Collodion
(b) Cellophane
(c) Both (a) and (b)
(d) None of the options
Answer: (c) Both (a) and (b)
In simple words: Ultrafiltration is a very fine way to separate tiny particles from a liquid. To do this, special filters called ultrafilters are used, which can be made from materials like collodion or cellophane. These materials have very small holes.

🎯 Exam Tip: Ultrafiltration uses specialized membranes with extremely small pores to separate colloidal particles from dissolved solutes and the dispersion medium under pressure.

Question 48. Collodion is 4% solution of ................................ in a mixture of alcohol and water.
(a) Cellulose acetate
(b) Cellulose sulphate
(c) Chloro cellulose
(d) Nitrocellulose
Answer: (d) Nitrocellulose
In simple words: Collodion is a special mixture often used in labs. It is made by dissolving nitrocellulose (a type of treated cotton) in a mix of alcohol and water. This solution is used for making ultrafilters.

🎯 Exam Tip: Collodion membranes, prepared from nitrocellulose solutions, are commonly used for separating colloidal particles during ultrafiltration.

Question 49. Blue colour of the sky in nature is due to
(a) Brownian movement
(b) Tyndall effect
(c) Both (a) and (b)
(d) None of the options
Answer: (b) Tyndall effect
In simple words: The blue color of the sky happens because sunlight hits tiny particles and water droplets in the air. These tiny particles scatter the blue part of the sunlight in all directions, making the sky look blue. This scattering is called the Tyndall effect.

🎯 Exam Tip: The Tyndall effect is the scattering of light by colloidal particles, making the path of the light beam visible. It is a key characteristic of colloids.

Question 50. Scattering of light by colloidal particles is known as
(a) Brownian movement
(b) Tyndall effect
(c) Electrophoresis
(d) Electro osmosis
Answer: (b) Tyndall effect
In simple words: When light shines through a colloid, the tiny particles in the colloid spread the light in different directions. This makes the path of the light visible, like a flashlight beam in a dusty room. This is called the Tyndall effect.

🎯 Exam Tip: The Tyndall effect distinguishes colloidal solutions from true solutions because true solutions do not scatter light to a visible extent.

II. Match the following

Question 1. Match the following.