Chapter 5: Surface Chemistry Class 12 Chemistry NCERT Solutions
Learn about adsorption, catalysis, colloids, and emulsions through Chapter 5 Surface Chemistry NCERT Solutions. Simplify complex topics for easier understanding. Download free PDFs and revise concepts quickly. Scroll below for all solved exercises.
What You Will Learn in Chapter 5 – Surface Chemistry
Surface Chemistry focuses on chemical processes that occur at the interface between different phases (solid-liquid, liquid-gas, etc.). This includes an in-depth study of adsorption, catalysis, and colloidal systems, all of which have significant real-world applications in industries and biological systems.
Key topics covered in this chapter include:
Adsorption and types of adsorption
Factors influencing adsorption of gases on solids
Freundlich and Langmuir adsorption isotherms
Catalysis and its types – homogeneous and heterogeneous
Mechanism of catalytic reactions
Enzyme catalysis and its applications
Colloids: types, properties, and preparation methods
Emulsions and their characteristics
Coagulation and protection of colloids
By mastering these core topics, students will develop the ability to apply these concepts to industrial processes, environmental chemistry, and biological systems.
Why Use Our NCERT Solutions for Chapter 5?
Surface Chemistry involves detailed theoretical explanations supported by scientific reasoning and practical applications. Our expertly crafted NCERT solutions provide step-by-step answers, simplified explanations, and conceptual clarity for every question, making it easier for students to understand and retain the information.
Key features of our solutions:
Clear, concise answers written in exam-friendly language
Step-by-step derivations and illustrations
Detailed explanation of concepts like adsorption isotherms and catalysis
Real-life examples to make concepts relatable
Solutions adhere strictly to NCERT and CBSE guidelines
Whether you’re revising before your CBSE board exam or preparing for entrance tests, these solutions are your perfect study companion.
Download Chapter 5 – Surface Chemistry NCERT Solutions PDF
We also provide a free downloadable PDF of Class 12 Chemistry Chapter 5 solutions. This easy-to-use document is perfect for offline study, last-minute revisions, and quick concept recaps without needing internet access.
Benefits of the PDF download:
Study anytime, anywhere without interruptions
Clean and organized layout for fast learning
All key questions and answers in one file
Ideal for both daily revision and exam preparation
Use the link on this page to download your Class 12 Chapter 5 Surface Chemistry NCERT Solutions PDF now.
Important Concepts to Focus On:
Before moving forward, ensure you have a strong grasp of these critical topics:
Adsorption vs. Absorption
Types of Adsorption and influencing factors
Freundlich and Langmuir Adsorption Isotherms
Catalysis mechanisms and industrial applications
Properties and classifications of colloids
Differences between true solutions, colloids, and suspensions
Coagulation and protection of colloids
Emulsions and their types
Begin Your Chapter 5 Learning Journey
Scroll down to explore the fully solved NCERT exercises for Chapter 5 – Surface Chemistry. Whether it’s conceptual theory, definitions, or application-based questions, our solutions offer clear guidance to help you understand, apply, and score high in your exams.
Understanding surface chemistry is key to numerous technological, biological, and environmental advancements. With our NCERT solutions, you’ll be well-equipped to tackle even the trickiest questions with ease and confidence.
| Section Name | Topic Name |
|---|---|
|
5 |
Surface Chemistry |
|
5.1 |
Adsorption |
|
5.2 |
Catalysis |
|
5.3 |
Colloids |
|
5.4 |
Classification of Colloids |
|
5.5 |
Emulsions |
|
5.6 |
Colloids Around Us |
NCERT Solutions for Class 12 Chemistry Chapter 5 – Surface Chemistry (Exercises)
Question 5.1: Distinguish between the meaning of the terms adsorption and absorption. Give one example of each.
Answer:
Adsorption is the accumulation of particles like atoms or molecules only on the surface of a substance.
Example: Ammonia gas adsorbed on activated charcoal.
Absorption is the process where a substance uniformly enters the bulk of another substance.
Example: Ammonia absorbed in water to form ammonium hydroxide.
Question 5.2: What is the difference between physical adsorption and chemisorption?
Answer:
| Property | Physisorption | Chemisorption |
|---|---|---|
| Nature of forces | Weak van der Waals’ forces | Strong chemical bonds |
| Enthalpy of adsorption | Low (20–40 kJ/mol) | High (80–240 kJ/mol) |
| Temperature dependency | Favours low temperature | Favours high temperature |
| Reversibility | Reversible | Irreversible |
| Specificity | Not specific | Highly specific |
| Number of layers | Multilayer possible | Monolayer only |
| Activation energy | Not required | Often required |
| Change in state of adsorbate | No change | May change due to reaction |
Question 5.3: Give reason why a finely divided substance is more effective as an adsorbent?
Answer: Finely divided substances offer a larger surface area, increasing the number of sites available for adsorption, making them more effective.
Question 5.4: What are the factors which influence the adsorption of a gas on a solid?
Answer:
• Nature of adsorbate and adsorbent
• Surface area of adsorbent
• Activation of adsorbent (e.g., heating)
• Pressure: adsorption increases with pressure
• Temperature: adsorption decreases with rise in temperature
Question 5.5: What is an adsorption isotherm? Describe Freundlich adsorption isotherm.
Answer:
An adsorption isotherm describes how the amount of gas adsorbed on a solid varies with pressure at constant temperature.
Freundlich Adsorption Isotherm:
x/m = k P^(1/n)
Taking logarithm: log(x/m) = log k + (1/n) log P
When plotted, log(x/m) vs log P gives a straight line confirming the Freundlich isotherm.
It holds well at low pressures and for physical adsorption.
Question 5.6: What do you understand by activation of adsorbent? How is it achieved?
Answer:
Activation refers to increasing the adsorptive power by enlarging surface area or exposing active sites.
It is achieved by heating, chemical treatment, or grinding into fine powder.
Question 5.7: What role does adsorption play in heterogeneous catalysis?
Answer: Reactants adsorb on the catalyst surface, leading to higher concentration, bond weakening, and enhanced reaction. Products desorb after formation.
Question 5.8: Why is adsorption always exothermic?
Answer: Adsorption decreases entropy (ΔS negative), and for spontaneity (ΔG negative), ΔH must be negative, indicating that adsorption is an exothermic process.
Question 5.9: How are the colloidal solutions classified on the basis of physical states of the dispersed phase and dispersion medium?
Answer:
| Dispersed Phase | Dispersion Medium | Type | Example |
|---|---|---|---|
| Solid | Liquid | Sol | Paint |
| Liquid | Gas | Aerosol | Fog |
| Gas | Solid | Solid Foam | Pumice stone |
Question 5.10: Discuss the effect of pressure and temperature on the adsorption of gases on solids.
Answer:
• Pressure: Adsorption increases with pressure until saturation.
• Temperature: Adsorption decreases with rising temperature due to exothermic nature.
Question 5.11: What are lyophilic and lyophobic sols? Give one example of each type. Why are hydrophilic sols more stable than hydrophobic sols?
Answer:
Lyophilic sols: High solvent affinity, e.g., starch sol.
Lyophobic sols: Low solvent affinity, e.g., gold sol.
Hydrophilic sols are more stable because they are heavily solvated and resist coagulation.
Question 5.12: Describe the essential features of enzyme catalysis.
Answer:
• Highly efficient
• Specific to substrates
• Active under mild temperature and pH
• Optimum activity at specific conditions
• Can be inhibited by specific molecules
Question 5.13: What is the role of adsorption in production of vacuum?
Answer: Adsorbents like activated charcoal trap residual gases, helping maintain a high vacuum.
Question 5.14: What is the role of adsorption in heterogeneous catalysis?
Answer: Adsorption enables reactants to adhere and align on catalyst surface, facilitating reaction, followed by product desorption.
Question 5.15: Why is adsorption always exothermic?
Answer: Because entropy decreases, ΔH must be negative (heat released) to make ΔG negative and process spontaneous.
Question 5.16: How is the adsorption of a gas related to its critical temperature?
Answer: Higher critical temperature means stronger intermolecular forces, thus greater adsorption tendency.
Question 5.17: What do you understand by activation of adsorbent?
Answer: Increasing adsorptive capacity by heating, grinding, or chemical treatments to expose more active surface sites.
Question 5.18: What role does adsorption play in heterogeneous catalysis?
Answer: Adsorption concentrates reactants on catalyst surface, weakens bonds, and facilitates product formation, followed by desorption.
Question 5.19: Why is adsorption always exothermic?
Answer: Adsorption reduces entropy; for spontaneity, heat must be released making it exothermic.
Question 5.20: How are colloids classified based on the nature of interaction between dispersed phase and dispersion medium?
Answer:
Lyophilic colloids: Strong interaction (e.g., gelatin in water).
Lyophobic colloids: Weak or no interaction (e.g., gold sol).
Question 5.21: Discuss the role of emulsifier in forming an emulsion.
Answer: Emulsifiers stabilize emulsions by forming a protective film around dispersed droplets and reducing surface tension. Examples: soap, gelatin.
Question 5.22: What is demulsification? Name two demulsifiers.
Answer:
Demulsification is the breaking of an emulsion into separate components.
Examples of demulsifiers: heating, addition of acids or salts like alum.