CBSE Class 12 Chemistry Chapter 2: Solutions NCERT Solutions

Reviewed by · Updated on

NCERT Solutions PDF Class 12 PDF

CBSE Class 12 Chemistry Chapter 2 Solutions delve into the essential concepts of solutions. This chapter explores various ways to express concentration, such as mole fraction and molality, and their connection to vapor pressure via Henry's Law. It also examines the factors influencing solubility, like temperature and the physical state of the solute and solvent. The solutions clarify the dynamic equilibrium between dissolving and crystallizing, differentiating between saturated, unsaturated, and supersaturated solutions. Furthermore, the text explains deviations from Raoult's Law, with a focus on positive deviations, and discusses how atmospheric pressure affects oxygen concentration at higher altitudes. These explanations aim to solidify students' understanding of solution principles, aiding their preparation for board exams.

Home

Quick info

BoardCBSE
ClassClass 12
SubjectChemistry Exemplar
Session2026
LanguageEnglish
TypeNCERT Solutions
ChapterChapter 2

Chapter summary

Chapter 2 of the CBSE Class 12 Chemistry syllabus, 'Solutions', is thoroughly explained with NCERT Solutions. This chapter covers essential topics like the various ways to express solution concentration (mole fraction, molality, etc.), the relationship between vapor pressure and concentration, Henry's Law, solubility of solids in liquids and gases in liquids, and the concept of equilibrium in solutions. It also addresses factors influencing solubility, types of solutions (saturated, unsaturated, supersaturated), and deviations from Raoult's law, including positive and negative deviations. The solutions provide clear explanations and step-by-step problem-solving for MCQs.

Learning outcomes

  • Understand the relationship between concentration units and vapor pressure using Henry's Law.
  • Analyze the effect of temperature and physical state on the rate of dissolution.
  • Differentiate between saturated, unsaturated, and supersaturated solutions.
  • Explain the factors affecting the solubility of solid solutes in liquid solvents.
  • Identify mixtures exhibiting positive deviation from Raoult's law.
  • Explain the effect of low atmospheric pressure on oxygen concentration at high altitudes.

Topics covered

Paper topics

  • Types of Solutions
  • Expressing Concentration of Solutions
  • Solubility
  • Vapour Pressure of Liquid Solutions
  • Raoult's Law
  • Ideal and Non-ideal Solutions
  • Azeotropes
  • Colligative Properties
  • Abnormal Molecular Mass

Important topics

  • Expressing Concentration of Solutions (Mole Fraction, Molality)
  • Henry's Law and its applications
  • Raoult's Law and Deviations (Positive and Negative)
  • Colligative Properties
  • Factors Affecting Solubility

PDF preview

Read page by page below. PDF is streamed from the official NCERT website — no download button on this page.

Loading document …
Page of
Loading page …

Questions and Solutions

Multiple Choice Questions (MCQs) - Q.1

Q.1 Which of the following units is useful in relating concentration of solution with its vapour pressure?
  1. Mole fraction
  2. Parts per million
  3. Mass percentage
  4. Molality
Solution: The correct unit for relating the concentration of a solution with its vapour pressure is mole fraction. According to Henry's law, the partial pressure of a gas above a solution is directly proportional to the mole fraction of the gas in the solution. The relationship is expressed as p = K_H x, where p is the partial pressure, x is the mole fraction, and K_H is Henry's constant. Therefore, mole fraction is the most appropriate unit for this context.

Answer: (a) Mole fraction

Multiple Choice Questions (MCQs) - Q.2

Q. 2 On dissolving sugar in water at room temperature, the solution feels cool to touch. Under which of the following cases will the dissolution of sugar be most rapid?
  1. Sugar crystals in cold water
  2. Sugar crystals in hot water
  3. Powdered sugar in cold water
  4. Powdered sugar in hot water
Solution: The dissolution of sugar in water is an endothermic process, meaning it absorbs heat from the surroundings, causing the solution to feel cool. The rate of dissolution is influenced by factors such as temperature and the surface area of the solute. Dissolution is generally faster at higher temperatures because the kinetic energy of the solvent molecules is greater, leading to more frequent and energetic collisions with the solute. Furthermore, using powdered sugar instead of sugar crystals significantly increases the surface area available for dissolution, allowing the solvent to interact with more solute particles simultaneously. Therefore, the dissolution of sugar will be most rapid when using powdered sugar in hot water.

Answer: (d) Powdered sugar in hot water

Multiple Choice Questions (MCQs) - Q.3

Q. 3 At equilibrium, the rate of dissolution of a solid solute in a volatile liquid solvent is .........
  1. less than the rate of crystallisation
  2. greater than the rate of crystallisation
  3. equal to the rate of crystallisation
  4. zero
Solution: Chemical equilibrium is a dynamic state where the rate of the forward process is equal to the rate of the reverse process. In the context of dissolving a solid solute in a volatile liquid solvent, equilibrium is reached when the rate at which the solid solute dissolves into the liquid becomes exactly equal to the rate at which the dissolved solute crystallizes out of the solution. At this point, there is no net change in the concentration of the dissolved solute.

Answer: (c) equal to the rate of crystallisation

Multiple Choice Questions (MCQs) - Q.4

Q. 4 A beaker contains a solution of substance 'A'. Precipitation of substance 'A' takes place when a small amount of 'A' is added to the solution. The solution is ........
  1. saturated
  2. supersaturated
  3. unsaturated
  4. concentrated
Solution: When a small amount of solute is added to a solution and it causes precipitation, it indicates that the solution already holds the maximum amount of solute it can dissolve at that temperature and pressure. Such a solution is called a saturated solution. If the added solute dissolves, the solution is unsaturated. A supersaturated solution contains more dissolved solute than a saturated solution and is unstable; adding a seed crystal can cause the excess solute to precipitate.

Answer: (a) saturated

Multiple Choice Questions (MCQs) - Q.5

Q. 5 The maximum amount of a solid solute that can be dissolved in a specified amount of a given liquid solvent does not depend upon .........
  1. temperature
  2. nature of solute
  3. pressure
  4. nature of solvent
Solution: The solubility of a solid solute in a liquid solvent is primarily influenced by the nature of the solute and solvent, and the temperature. Pressure has a negligible effect on the solubility of solids in liquids because both solids and liquids are practically incompressible. Therefore, the maximum amount of solid solute that can be dissolved does not significantly depend on pressure.

Answer: (c) pressure

Multiple Choice Questions (MCQs) - Q.6

Q. 6 Low concentration of oxygen in the blood and tissues of people living at high altitude is due to ..........
  1. low temperature
  2. low atmospheric pressure
  3. high atmospheric pressure
  4. Both low temperature and high atmospheric pressure
Solution: At high altitudes, the atmospheric pressure is significantly lower than at sea level. According to Henry's law, the solubility of a gas in a liquid (like oxygen in blood) is directly proportional to the partial pressure of that gas above the liquid. Since the atmospheric pressure is lower at high altitudes, the partial pressure of oxygen is also lower, resulting in less oxygen dissolving in the blood and tissues.

Answer: (b) low atmospheric pressure

Multiple Choice Questions (MCQs) - Q.7

Q. 7 Considering the formation, breaking and strength of hydrogen bond, predict which of the following mixtures will show a positive deviation from Raoult's law?
  1. Methanol and acetone
  2. Chloroform and acetone
  3. Nitric acid and water
  4. Phenol and aniline
Solution: A positive deviation from Raoult's law occurs when the intermolecular attractive forces between the solute-solvent molecules are weaker than the forces between the solute-solute molecules and solvent-solvent molecules. In the mixture of methanol and acetone, pure methanol has strong hydrogen bonding between its molecules. When acetone is added, its molecules intersperse among the methanol molecules, disrupting and weakening the existing hydrogen bonds between methanol molecules. This leads to weaker overall intermolecular forces in the mixture compared to the pure components, resulting in a higher vapor pressure than predicted by Raoult's law (positive deviation).

Answer: (a) Methanol and acetone

Common mistakes

  • Confusing the conditions for rapid dissolution (e.g., powdered vs. crystal, hot vs. cold).
  • Misinterpreting the equilibrium condition in solutions.
  • Incorrectly classifying solutions as saturated, unsaturated, or supersaturated.
  • Not understanding the relationship between intermolecular forces and deviations from Raoult's law.

Revision tips

  • Focus on understanding the definitions and conditions for different types of solutions (saturated, unsaturated, supersaturated).
  • Memorize the formula relating partial pressure and mole fraction (Henry's Law) and its applications.
  • Pay close attention to the factors affecting solubility and deviations from Raoult's law.
  • Review the MCQs to reinforce concepts related to concentration units and solution behavior.

Practice MCQs

Q1. Which of the following units is most useful in relating the concentration of a solution to its vapor pressure?

Q2. Under which conditions will the dissolution of sugar in water be most rapid?

Q3. At equilibrium, the rate of dissolution of a solid solute in a volatile liquid solvent is:

Q4. If adding a small amount of solute 'A' to a solution of 'A' causes precipitation, the solution is:

Q5. The maximum amount of a solid solute that can dissolve in a fixed amount of solvent at a specific temperature is independent of:

Q6. Low concentration of oxygen in the blood of people living at high altitudes is primarily due to:

Q7. Which mixture is expected to show a positive deviation from Raoult's law?

Frequently asked questions

What are the key concepts covered in CBSE Class 12 Chemistry Chapter 2 Solutions?

Chapter 2 covers types of solutions, methods to express concentration (like mole fraction, molality), solubility of solids and gases, vapor pressure of liquid solutions, Raoult's law, ideal and non-ideal solutions, azeotropes, and colligative properties.

How do these NCERT Solutions help in understanding Raoult's Law?

The solutions explain Raoult's law and differentiate between ideal solutions and non-ideal solutions, including mixtures that show positive and negative deviations, providing clarity on the behavior of solutions.

What is the significance of mole fraction in relation to vapor pressure?

Mole fraction is crucial as it directly relates to the partial pressure of a gas in a solution, as described by Henry's Law (p = K_H x), making it a key unit for understanding vapor pressure behavior.

How do the solutions explain the rapid dissolution of sugar?

The solutions explain that dissolution is most rapid for powdered sugar in hot water due to increased surface area and the endothermic nature of sugar dissolution, which is favored by higher temperatures.

What causes low oxygen levels at high altitudes, according to the solutions?

Low oxygen levels at high altitudes are attributed to low atmospheric pressure, which reduces the partial pressure of oxygen, leading to less oxygen dissolving in the blood.

Are all types of solutions covered in these NCERT Solutions?

Yes, the solutions cover various types of solutions, including saturated, unsaturated, and supersaturated solutions, and explain the conditions under which precipitation occurs.

Important links

Content reviewed by the NCERT Help team. Editorial Team and update policy

NCERT Solutions PDF PDF on NCERT Help. URL unchanged for search indexing.