NCERT Solutions for Class 12 Chemistry Chapter 1 - Solutions
The chapter Solutions is one of the most calculation-friendly and concept-rich topics in the Class 12 Chemistry syllabus. It deals with how two or more substances mix to form a homogeneous mixture and how we measure and predict the behaviour of these mixtures. Students learn about different ways of expressing concentration, the nature of solubility, vapour pressure, Raoult's law, and colligative properties such as elevation in boiling point, depression in freezing point, and osmotic pressure. The chapter also explains deviations from ideal behaviour and the van't Hoff factor, which connects solution chemistry with electrolytic dissociation.
For Subject Wise NCERT Solutions for class 12 and Chapter-wise NCERT solutions for class 12 Chemistry, check out these pages.
Find the PDF of All the Exercises of NCERT Class 12 Chemistry Chapter 1 Solutions
All in-text and end-of-chapter exercise answers for the Solutions chapter are available in an easy-to-download PDF format. This allows students to revise formulas, definitions, and numerical methods offline, without needing constant internet access. The PDF is especially useful during last-minute board exam revision and while practising numerical problems repeatedly for speed and accuracy.
This chapter carries good weightage in the CBSE board exam and is equally important for JEE and NEET, since numerical problems based on colligative properties and concentration terms are frequently asked. A strong grip on this chapter also helps in understanding electrochemistry and chemical kinetics later, as solutions form the base for many reaction-based calculations.
Using NCERT Solutions for Class 12 Chemistry for this chapter helps students approach each textbook question with a clear, step-by-step method instead of memorising answers blindly. The NCERT Solutions Class 12 Chemistry Chapter 1 set is designed to simplify tricky derivations, clarify units, and build the confidence needed to solve both direct and application-based questions during revision.
Important Topics Covered in NCERT Class 12 Chemistry Chapter 1
The chapter begins with types of solutions based on the physical state of solute and solvent, followed by ways of expressing concentration—mass percentage, mole fraction, molarity, and molality. Students then study solubility of gases and solids in liquids, along with Henry's law. A major portion focuses on vapour pressure of liquid solutions and Raoult's law, leading into ideal and non-ideal solutions and the reasons behind positive and negative deviations.
The chapter then covers the four colligative properties—relative lowering of vapour pressure, elevation in boiling point, depression in freezing point, and osmotic pressure—each with its derivation and real-world relevance. Finally, students learn about abnormal molar mass and the van't Hoff factor, which explains association and dissociation of solutes in solution.
Important Formulas and Key Points of Chapter 1
Formula / Concept | Explanation / Application |
|---|---|
Mass percentage = (Mass of solute / Mass of solution) × 100 | Used to express concentration when both solute and solvent mass are known. |
Mole fraction (x) = moles of component / total moles of all components | A unit-free way to express concentration, useful in vapour pressure calculations. |
Molarity (M) = moles of solute / volume of solution (in L) | Most commonly used unit in titrations and lab-based calculations; varies with temperature. |
Molality (m) = moles of solute / mass of solvent (in kg) | Independent of temperature, preferred for colligative property calculations. |
Henry's Law: p = KH · x | Relates partial pressure of a gas to its mole fraction in solution; explains solubility of gases. |
Raoult's Law: ptotal = p°AxA + p°BxB | Applies to ideal solutions; total vapour pressure depends on mole fraction of each component. |
Relative lowering of vapour pressure = (p° − ps) / p° = xsolute | A colligative property used to determine molar mass of a non-volatile solute. |
ΔTb = Kb × m | Elevation in boiling point; Kb is the molal boiling point elevation constant. |
ΔTf = Kf × m | Depression in freezing point; Kf is the molal freezing point depression constant. |
Osmotic pressure: π = CRT | C is molar concentration; used to find molar mass of macromolecules like proteins. |
van't Hoff factor (i) = Observed colligative property / Calculated colligative property | Accounts for dissociation (i > 1) or association (i < 1) of solute particles. |
Modified colligative property equations (with i) | e.g., π = iCRT; used for electrolytic solutions showing abnormal behaviour. |
Molality is preferred over molarity in colligative property problems because it does not change with temperature.
Ideal solutions obey Raoult's law across the entire concentration range with ΔHmix = 0.
Positive deviation occurs when A–B interactions are weaker than A–A and B–B interactions.
Negative deviation occurs when A–B interactions are stronger than A–A and B–B interactions.
Azeotropes are mixtures that boil at a constant temperature and cannot be separated by simple distillation.
Osmotic pressure is widely tested numerically because it directly gives molar mass of large molecules.
For electrolytes that dissociate, i > 1; for solutes that associate (like benzoic acid in benzene), i < 1.
Always convert volume units carefully (mL to L) before applying the molarity formula.
Reverse osmosis is a frequently asked application based on osmotic pressure.
Do not confuse molarity (per litre of solution) with molality (per kg of solvent)—a common scoring mistake.
Vapour pressure lowering is a colligative property; it depends only on the number of solute particles, not their identity.
Remember the units: Kb and Kf are expressed in K kg mol⁻¹.
For numerical accuracy, always check whether the solute is a strong electrolyte, weak electrolyte, or non-electrolyte before applying the van't Hoff factor.
Detailed Explanation of NCERT Class 12 Chemistry Chapter 1
Solutions form the backbone of countless real-life and laboratory processes, from the way medicines dissolve in blood plasma to how seawater becomes drinkable through reverse osmosis. This chapter trains students to think quantitatively about mixtures—not just qualitatively. Once you understand why molality stays constant with temperature while molarity does not, several confusing numerical questions start making intuitive sense rather than feeling like rote formulas.
A major real-life application lies in colligative properties. Adding salt to icy roads in winter works because of freezing point depression. Saline drips used in hospitals are designed using osmotic pressure principles so that they match the concentration of body fluids. These connections make the chapter far more relatable than it first appears in textbook language.
Most students lose marks not because the concepts are hard, but because of careless unit handling—mixing up grams with kilograms, or litres with millilitres, while applying molarity and molality formulas. Another common error is forgetting to include the van't Hoff factor when the solute is an electrolyte, which leads to incorrect colligative property values. Practising a wide variety of numericals, rather than only formula-based plug-in questions, builds the real exam-readiness needed for board-level and competitive-level papers.
For scoring well, focus on writing derivations neatly with correct steps, since CBSE awards stepwise marks even if the final numerical answer has a small error. Diagrams showing vapour pressure curves for ideal and non-ideal solutions are also often asked and should be practised separately.
This chapter connects directly to Electrochemistry, where concentration terms like molarity reappear in Nernst equation calculations, and to Chemical Kinetics, where solution concentration determines reaction rates. Building a solid foundation here therefore pays off across the rest of the Class 12 Chemistry syllabus.