Most Challenging Class 12th Chemistry Problems and Tips to Solve
Challenging Class 12th Chemistry Problems: Class 12 Chemistry includes both theoretical concepts and numerical problems. A thorough conceptual clarity and effective application is essential to accurately solve class 12 Chemistry questions. Therefore, many students often find Chemistry challenging.
Mastering Chemistry is not only essential to score good marks in board exams but also to ace competitive exams like JEE and NEET. to effectively prepare for class 12 Chemistry, candidates should follow a strategic preparation approach and focus on understanding the concepts of difficult topics. Additionally, candidates should solve the most challenging class 12th Chemistry problems to strengthen concept application and accuracy in answering questions.
Common Challenges in Class 12 Chemistry
Although Chemistry is a scoring subject in class 12, students find it challenging because of the following aspects:
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Conceptual Understanding: Topics such as electrochemical reactions and reaction mechanisms include processes happening at the molecular or atomic level. Therefore, students find it challenging to visualise and comprehend them.
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Application vs. Memorisation: Chemistry often requires applying concepts to solve problems. Therefore, it necessitates a comprehensive understanding beyond rote learning.
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Numerical Problems: Precision and accuracy are crucial in solving numerical problems. Therefore, it is recommended for candidates to practise various types of questions during the preparation phase.
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Organic Reaction Mechanisms: Understanding the details of organic reactions requires conceptual clarity. Many students struggle to effectively understand organic reactions, which makes Chemistry challenging.
Most Challenging Class 12th Chemistry Problems and Tips to Solve
While there are several relatively easier chapters in Class 12 Chemistry, some chapters are challenging for students. To master these chapters, candidates must solve tough questions from them. Here are the chapter-wise most challenging class 12th Chemistry problems with tips to solve them:
Thermodynamics
Thermodynamics focus on the principles that govern energy changes in chemical reactions. This chapter includes concepts like enthalpy, entropy, and Gibbs free energy. Students find this chapter challenging as it includes understanding how the thermodynamic properties interact and how they apply to different chemical processes. The abstract nature of these concepts often makes it challenging for students to visualise and solve related problems effectively.
Question: For the reaction:
N2(g)+3H2(g)→2NH3(g)→2NH3(g)
at 298 K, the enthalpy change (ΔH∘) is –92.4 kJ/mol, and the entropy change (ΔS∘) is –198.3 J/K·mol.
(a) Calculate the Gibbs free energy change (ΔG∘) for the reaction at 298 K.
(b) Predict whether the reaction is spontaneous at this temperature.
(c) Determine the temperature at which the reaction becomes non-spontaneous.
Tip to solve:
Use the Gibbs free energy equation:
ΔG∘=ΔH∘−TΔS∘−TΔS∘
Set ΔG∘=0 to find the temperature at which spontaneity changes.
Aldehydes, Ketones, and Carboxylic Acids
This class 12 Chemistry chapter includes the properties, reactions, and mechanisms of organic compounds like aldehydes, ketones, and carboxylic acids. The challenge lies in mastering various reaction mechanisms, such as nucleophilic addition, and understanding the behaviour of these compounds in different chemical reactions. To solve questions accurately, students must memorise and gain a thorough understanding of their reactivity patterns.
Question: Predict the product and write the mechanism for the following reaction:
CH3CHO+CH3MgBr→?
Followed by hydrolysis with dilute HCl.
Additionally, explain what happens when acetaldehyde undergoes aldol condensation with itself in the presence of dilute NaOH. Write the balanced chemical equations for both reactions.
Tip to solve:
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The reaction with CH3MgBr involves Grignard reagent addition, forming an alcohol upon hydrolysis.
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For aldol condensation, consider enolate ion formation followed by nucleophilic attack on another molecule of acetaldehyde.
Biomolecules
In this chapter of class 12 Chemistry, students study the structure and function of important biomolecules, including carbohydrates, proteins, and nucleic acids. Students find it challenging to understand the complexity of molecular structures and the functions they perform in biological systems. Additionally, students need to focus on memorising the details of these biomolecules and understanding their biological significance with consistent revision.
Question: (a) Draw the structure of D-glucose and explain its cyclic (pyranose) form.
(b) Describe the formation of a dipeptide using glycine and alanine. Write the reaction showing peptide bond formation.
(c) Explain how enzymes act as biocatalysts and mention two factors affecting enzyme activity with reasons.
Tip to solve:
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For part (a), show the conversion of D-glucose from its open-chain form to the cyclic hemiacetal form.
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For part (b), write the condensation reaction showing the elimination of water during peptide bond formation.
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For part (c), consider factors such as temperature and pH affecting enzyme structure and function.
Electrochemistry
Electrochemistry is often regarded as one of the most challenging topics in Class 12 Chemistry. It focuses on the relationship between chemical reactions and electrical energy. Additionally, students have to cover concepts like galvanic cells, electrolysis, and standard electrode potential.
Concepts such as the Nernst equation, electrochemical series, and the calculation of cell potentials are particularly challenging for students. To solve numerical questions in Electrochemistry, students have to apply these concepts, which most students find very difficult. To master this chapter, it is essential to have a strong theoretical understanding and the ability to apply mathematical principles to solve problems effectively.
Question: Calculate the EMF of a cell using the following reaction at 25°C:
Zn(s)+Cu2+(aq)→Zn2+(aq)+Cu(s)
Given:
E°Zn2+/Zn = −0.76 V , E°Cu2+/Cu = +0.34 V
If the concentration of Zn2+ is 0.01 M and Cu2+ is 1 M, calculate the cell potential using the Nernst equation.
Tip to solve
Use the Nernst equation:
Ecell = E°cell − 0.0591nlog[Zn2+][Cu2+]
Chemical Kinetics
This chapter explains how to calculate the rate at which chemical reactions occur and the factors that influence these rates. Many students find it challenging due to the mathematical equations involved in calculating reaction rates and rate laws. Additionally, grasping how temperature and concentration affect reaction speed makes this chapter specifically challenging for many students. Effective conceptual understanding and problem-solving skills are necessary to accurately answer Chemical Kinetics questions in class 12.
Question: A reaction A→B follows first-order kinetics. The concentration of A decreases from 0.8 M to 0.2 M in 40 minutes. Calculate the rate constant and half-life of the reaction.
Tip to solve:
Use the first-order integrated rate law:
In [A]0/[A] = k.t
Identify [A]0 (initial concentration), [A] (final concentration), and t (time) from the problem.
Substitute Known Values:
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[A]0=0.8 M, [A] = 0.2 M, t = 40 minutes
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Substitute these into the rate law: ln 0.80.2 =k⋅40
Challenging Class 12th Chemistry Problems FAQs
Q1. What is the hardest lesson in Chemistry class 12?
Ans. Electrochemistry and Chemical Kinetics are the most challenging chapters in class 12 Chemistry.
Q2. What is the best way to study class 12 Chemistry?
Ans. The best way to study class 12 Chemistry includes understanding the concepts and then solving various types of questions from each chapter. After completing a chapter, students should check their answers to find the areas of improvement. Further, they should revise the challenging sections to gein conceptual clarity.
Q3. How can I memorise chemistry easily?
Ans. To memorise CHemistry easily, students should divide the chapters into small sections and focus on mastering one section at a time. Further, students should create notes by explaining each topic. Maintaining consistency is crucial to memorise Chemistry.
Q4. What are the memory techniques for chemistry?
Ans. Regular revision is the most effective technique to memorise Chemistry concepts.
