Class 12 Chemistry Notes Chapter 18 (Model Question Papers) – Examplar Problems Book

Detailed Notes with MCQs of Chapter 18 of your NCERT Chemistry Exemplar book. Now, this chapter isn't like the others with specific concepts to learn; instead, it provides Model Question Papers. Think of these as blueprints or practice drills designed to simulate the actual board examination environment and, importantly for many of you, to solidify concepts frequently tested in various government exams that rely heavily on the NCERT syllabus.

Understanding the Purpose and Significance of Chapter 18: Model Question Papers

1. Exam Pattern Familiarization:

   • These papers are structured based on the typical pattern of the Class 12 Board Examination (or patterns prevalent at the time of the book's publication).
   • They give you a clear idea about the types of questions asked: Very Short Answer (VSA), Short Answer (SA I & SA II), Long Answer (LA), and sometimes Multiple Choice Questions (MCQs) or Case-Based Questions, depending on the prevailing pattern.
   • Understanding the distribution of marks across different question types and chapters is crucial for strategic preparation.

2. Comprehensive Syllabus Coverage:

   • Each model paper is designed to cover the entire Class 12 Chemistry syllabus.
   • Solving these papers helps ensure you haven't missed any significant topics or sub-topics from any chapter.
   • They integrate concepts from different chapters, testing your ability to connect ideas (e.g., applying concepts from Chemical Kinetics to a problem involving Electrochemistry).

3. Nature of Questions:

   • The questions are sourced from the NCERT textbook and Exemplar problems, reflecting the depth and standard expected.
   • You will find a mix of:
     • Knowledge-based questions: Recalling definitions, laws, properties (e.g., Define Kohlrausch's law).
     • Understanding-based questions: Explaining concepts, reasoning (e.g., Why are transition metals good catalysts?).
     • Application-based questions: Solving numerical problems, predicting products of reactions, applying concepts to specific scenarios (e.g., Calculate the EMF of a given cell).
     • Skill-based questions: Drawing structures, writing mechanisms, balancing equations.

4. Self-Assessment and Time Management:

   • This is perhaps the most critical use. Attempt these papers under strict, timed conditions (usually 3 hours).
   • This practice helps you:
     • Gauge your preparation level across the syllabus.
     • Identify your strong and weak areas. Which chapters or types of questions are you struggling with?
     • Improve your speed and accuracy.
     • Develop an effective strategy for attempting the actual exam – which sections to tackle first, how much time to allocate per question type.

5. Relevance for Government Exams (SSC, Railways, State PSCs, etc.):

   • Many government exams, especially those for science-related posts or general competitive exams with a science component, draw heavily from the NCERT syllabus up to Class 12.
   • While the pattern might differ (often more MCQs), the core concepts tested in the Exemplar model papers are fundamental.
   • Practicing these papers strengthens your conceptual clarity, problem-solving skills (especially numericals in Physical Chemistry, reasoning in Inorganic, and reactions/mechanisms in Organic), which are invaluable for objective-type questions in competitive exams. You learn to apply concepts quickly and accurately.

How to Use Chapter 18 Effectively:

1. Complete Syllabus First: Don't jump to model papers before thoroughly revising the entire syllabus at least once.
2. Simulate Exam Conditions: Find a quiet place, set a timer (usually 3 hours), and attempt the paper without referring to notes or books.
3. Honest Self-Evaluation: After finishing, use the NCERT solutions or consult your textbook/teacher to evaluate your answers critically. Don't just check the final answer for numericals; assess the steps and reasoning.
4. Analyze Performance:
   • Calculate your score realistically.
   • Note down the questions you answered incorrectly or couldn't attempt.
   • Categorize your mistakes: Conceptual error? Calculation mistake? Ran out of time? Forgot a formula/fact?
5. Targeted Revision: Use this analysis to guide your subsequent revision. Focus more on the chapters/topics/question types where you faced difficulty.
6. Repeat: Solve all the model papers provided in the Exemplar over time, tracking your improvement.

In essence, Chapter 18 is your practice ground. Use it wisely to refine your preparation, build confidence, and develop the exam temperament required for both board exams and competitive government exams.

Multiple Choice Questions (MCQs) based on Class 12 Chemistry Syllabus (Typical of Model Paper Level):

1. Which of the following exhibits the highest osmotic pressure at a given temperature?
   (a) 0.1 M Urea
   (b) 0.1 M Glucose
   (c) 0.1 M BaCl₂
   (d) 0.1 M NaCl

2. For the reaction A + 2B → C, the rate is given by Rate = k[A][B]. If the concentration of A is kept constant and the concentration of B is doubled, the rate of reaction will:
   (a) Double
   (b) Halve
   (c) Become four times
   (d) Remain unchanged

3. Which element among the following exhibits the maximum number of oxidation states?
   (a) Sc (Z=21)
   (b) Cr (Z=24)
   (c) Mn (Z=25)
   (d) Fe (Z=26)

4. The IUPAC name for the complex [Co(NH₃)₅Cl]Cl₂ is:
   (a) Pentaamminechloridocobalt(II) chloride
   (b) Chloridopentaamminecobalt(III) chloride
   (c) Pentaamminechloridocobalt(III) chloride
   (d) Dichloridopentaamminecobalt(III)

5. Which of the following reagents cannot be used to distinguish between ethanal and propanal?
   (a) Tollen's reagent
   (b) Fehling's solution
   (c) Iodoform test (I₂/NaOH)
   (d) Benedict's solution

6. Primary structure of a protein refers to:
   (a) The sequence of amino acids
   (b) The helical structure (α-helix)
   (c) The overall folding of the polypeptide chain
   (d) The arrangement of multiple subunits

7. Which of the following is an example of a thermosetting polymer?
   (a) Polythene
   (b) PVC
   (c) Bakelite
   (d) Nylon 6,6

8. The standard electrode potential (E°) values of Al³⁺/Al, Ag⁺/Ag, K⁺/K and Cr³⁺/Cr are -1.66 V, 0.80 V, -2.93 V and -0.74 V, respectively. The correct decreasing order of reducing power of the metal is:
   (a) Ag > Cr > Al > K
   (b) K > Al > Cr > Ag
   (c) Al > K > Ag > Cr
   (d) K > Al > Ag > Cr

9. SN1 reaction is favoured by:
   (a) Non-polar solvents
   (b) Polar protic solvents
   (c) Polar aprotic solvents
   (d) Non-polar aprotic solvents

10. Aniline reacts with bromine water at room temperature to give:
    (a) o-Bromoaniline
    (b) p-Bromoaniline
    (c) A mixture of o- and p-bromoaniline
    (d) 2,4,6-Tribromoaniline

Answer Key for MCQs:

1. (c) [Highest effective molar concentration due to dissociation: BaCl₂ → Ba²⁺ + 2Cl⁻ (i ≈ 3)]
2. (a) [Rate = k[A][2B] = 2 * (k[A][B]) = 2 * Initial Rate]
3. (c) [Mn shows oxidation states from +2 to +7]
4. (c) [Follow IUPAC nomenclature rules for coordination compounds]
5. (c) [Both ethanal and propanal are aldehydes without a methyl ketone group adjacent to the carbonyl, so neither gives a positive iodoform test. Both give positive tests with Tollen's, Fehling's, and Benedict's reagents.]
6. (a) [Definition of primary structure]
7. (c) [Bakelite becomes infusible on heating]
8. (b) [Lower (more negative) the E°, higher the reducing power. K (-2.93V) > Al (-1.66V) > Cr (-0.74V) > Ag (+0.80V)]
9. (b) [SN1 involves carbocation formation, stabilized by polar protic solvents]
10. (d) [Aniline is highly activating; reaction with Br₂(aq) leads to trisubstitution]