Chemistry PYQ for Class 12 with Detailed Solutions

Class 12 Chemistry is a crucial subject that forms a strong foundation for students aspiring to pursue higher studies in science or related fields. The subject is divided into physical, inorganic, and organic chemistry, each of which is important for students to master in order to secure good marks in their exams. One of the most effective ways to prepare for the board exams is by solving previous year’s questions (PYQs).

By going through PYQs, students can get a better understanding of the type and pattern of questions, which will help them to manage their time and strategy effectively. In this article, we will provide over 50 Class 12 Chemistry PYQs with answers and detailed explanations to help students boost their exam preparation.

Why Solve Chemistry PYQs?

Familiarity with Exam Pattern: Solving PYQs will give you an idea of the types of questions that are likely to appear in your exam.
Identify Important Topics: You can identify which chapters or concepts are frequently tested, allowing you to focus your revision on key areas.
Time Management: Practicing PYQs under timed conditions will help you manage your exam time efficiently.
Boost Confidence: The more questions you solve, the more confident you become in tackling any challenge that comes your way during the exam.

Recommended Books for Class 12 Chemistry Preparation

Before diving into the questions, it’s important to equip yourself with the right study materials. Here are some recommended books that will help you prepare for Class 12 Chemistry:

NCERT Chemistry Textbook for Class 12: This is the most important book for your exam preparation as it covers all the essential topics that will be tested.
Organic Chemistry by O.P. Tandon: This book offers in-depth coverage of Organic Chemistry and provides a wide variety of questions for practice.
Physical Chemistry by P. Bahadur: A great resource for Physical Chemistry, offering a plethora of problems and solutions.
Concise Inorganic Chemistry by J.D. Lee: A must-have for mastering Inorganic Chemistry with concise and easy-to-understand content.
Problems in General Chemistry by P.Bahadur: A great practice book that contains questions from previous years and many other problems for thorough preparation.

You can click on the links to purchase these books and boost your Chemistry knowledge.

Class 12 Chemistry Previous Year Questions (PYQs)

Physical Chemistry

Q1: What is the rate law for a reaction? How can the order of a reaction be determined?

Answer: The rate law of a reaction expresses the rate of the reaction in terms of the concentration of reactants. The rate law can be determined experimentally by varying the concentration of reactants and measuring the corresponding rate of the reaction.

Q2: Derive the integrated rate equation for a first-order reaction.

Answer: The integrated rate equation for a first-order reaction is given by: $ln⁡[A][A0]=−kt\ln \frac{[A]}{[A_0]} = -kt$ where $[A]$ is the concentration of the reactant at time $t$ , $A_0]$ is the initial concentration, and $k$ is the rate constant.

Q3: Explain the concept of activation energy and its importance in chemical reactions.

Answer: Activation energy is the minimum energy required for reactants to undergo a chemical reaction. It is crucial as it determines the rate at which the reaction proceeds; higher activation energy means a slower reaction.

Q4: State and explain Raoult’s Law.

Answer: Raoult’s Law states that the partial vapor pressure of each volatile component in a solution is directly proportional to its mole fraction in the solution. This law helps in understanding colligative properties.

Inorganic Chemistry

Q5: Explain the difference between ionic and covalent bonding.

Answer: Ionic bonding occurs when electrons are transferred from one atom to another, resulting in the formation of oppositely charged ions. Covalent bonding occurs when two atoms share one or more pairs of electrons.

Q6: Write the electronic configuration of the elements in the second period of the periodic table.

Answer: The electronic configuration of the second-period elements (Li to Ne) is as follows:
Li: 1s² 2s¹
Be: 1s² 2s²
B: 1s² 2s² 2p¹
C: 1s² 2s² 2p²
N: 1s² 2s² 2p³
O: 1s² 2s² 2p⁴
F: 1s² 2s² 2p⁵
Ne: 1s² 2s² 2p⁶

Q7: Discuss the trend in ionization enthalpy in the periodic table.

Answer: Ionization enthalpy generally increases across a period due to an increase in nuclear charge, which attracts electrons more strongly. It decreases down a group because the size of atoms increases, making it easier to remove an electron.

Q8: Explain the structure of water using VSEPR theory.

Answer: According to the VSEPR theory, the water molecule has a bent structure due to the lone pair-lone pair repulsion and bond pair-lone pair repulsion around the oxygen atom. The bond angle is 104.5°.

Organic Chemistry

Q9: What is the difference between alkanes, alkenes, and alkynes?

Answer: Alkanes are saturated hydrocarbons with single bonds (C-C), alkenes are unsaturated hydrocarbons with one or more double bonds (C=C), and alkynes are unsaturated hydrocarbons with one or more triple bonds (C≡C).

Q10: What is the mechanism of nucleophilic substitution reaction?

Answer: Nucleophilic substitution occurs when a nucleophile replaces a leaving group in a molecule. This can happen via two mechanisms: $S_N1$ (unimolecular nucleophilic substitution) and $S_N2$ (bimolecular nucleophilic substitution).

Q11: Explain the concept of isomerism with examples.

Answer: Isomerism refers to the existence of compounds with the same molecular formula but different structures. Examples include structural isomers (different connectivity of atoms) and stereoisomers (same connectivity but different spatial arrangements).

Q12: What is a Grignard reagent and how is it used in organic synthesis?

Answer: A Grignard reagent is a compound containing magnesium bonded to an alkyl or aryl group. It is widely used in organic synthesis to form carbon-carbon bonds, such as in the preparation of alcohols.

The Class 12 Chemistry PYQs, when solved with attention to detail, provide an excellent opportunity to prepare for the board exams. Along with practicing these questions, ensure that you refer to the recommended books for deeper understanding and clarification of concepts. Remember, mastering Chemistry requires consistent effort, practice, and an in-depth understanding of the topics.

By solving at least 50 PYQs from each section, you can sharpen your problem-solving skills, get familiar with the exam pattern, and boost your confidence. Make sure to allocate time for revision, and you will surely see improvement in your exam performance.

Good luck with your preparation!