CBSE Class 12 Chemistry Question with Answers for Practical Exams

The CBSE Board will be conducting the class 12th practical exams for the respective subjects in January 2026 month so that all the students who are studying in class 12th in the academic session 2025-26 can appear and score higher in them. It is crucial for all students to score as high as possible in the practical exams, as they contribute to the overall score of a student. Therefore, in this article, we have shared a list of CBSE Class 12 Chemistry Question with Answers for Practical Exams. Scroll down in the article and check the important questions.

CBSE Class 12 Chemistry Viva Questions

CBSE Class 12 Chemistry viva questions assess conceptual understanding of experiments, practical skills, theoretical principles, and real-world applications. Questions cover basic definitions (e.g., molarity), experiment-specific aspects (e.g., why a certain indicator is used), theoretical connections (e.g., role of a salt bridge), and practical application (e.g., industrial uses of buffer solutions). Strong preparation involves mastering the syllabus, practicing mock vivas, understanding the underlying theory of experiments, and maintaining a clear, organized lab record.

CBSE Class 12 Chemistry Question with Answers for Practical Exams

The CBSE Class 12 Chemistry practical exam is an important part of the board assessment. It carries 30 marks and tests a student’s ability to perform experiments, analyze results, and apply theoretical concepts in a practical setting. Along with lab work, the viva-voce (oral exam) plays a crucial role, where examiners test the student’s understanding through short questions. Preparing well for these questions helps in scoring full marks.

Q1. Why should distilled water be used in laboratory experiments?
Ans: Distilled water is free from dissolved salts and impurities that may interfere with reactions.

Q2. Why are chemicals stored in tightly closed bottles?
Ans: To prevent reaction with moisture, air, or light which may spoil the reagent.

Q3. Why is ethanol preferred over water for dissolving organic compounds?
Ans: Most organic compounds are insoluble in water but soluble in ethanol.

Q4. What is the difference between accuracy and precision in experiments?
Ans: Accuracy is closeness to the true value, while precision is repeatability of results.

Q5. Why is charcoal used for the borax bead test?
Ans: Charcoal provides a reducing environment for identifying metallic ions.

Q6. Why is sodium carbonate extract prepared for testing acidic radicals?
Ans: It converts insoluble salts into soluble sodium salts, making detection easier.

Q7. Why is lead nitrate used in the detection of halide ions?
Ans: Lead nitrate reacts with halide ions to form distinct precipitates useful for identification.

Q8. Why is dilute H2SO4 not used for detecting carbonate ions?
Ans: It reacts violently, releasing excessive CO2, which may lead to errors.

Q9. Why should the burette be filled below eye level?
Ans: To avoid parallax error and prevent accidents from acid/base splashing.

Q10. Why is the tip of the burette filled before titration?
Ans: To remove air bubbles which may cause inaccurate readings.

Q11. Why is a white tile placed below the conical flask during titration?
Ans: It makes the color change of the indicator more visible at the endpoint.

Q12. Why is oxalic acid heated before titration with KMnO₄?
Ans: Heat increases the rate of reaction between oxalic acid and KMnO₄.

Q13. Why is starch indicator added towards the end in iodometric titrations?
Ans: If added earlier, iodine forms a stable starch-iodine complex, making endpoint detection difficult.

Q14. Why does freezing point decrease when a solute is added?
Ans: Because solute particles lower the chemical potential of the solvent, causing depression in freezing point.

Q15. Why is KCl solution used for calibrating conductivity meters?
Ans: KCl has stable conductivity values at given concentrations and temperatures.

Q16. Why does molar conductivity of weak electrolytes increase sharply with dilution?
Ans: Dilution increases ionization, producing more free ions.

Q17. Why is surface tension measured at constant temperature?
Ans: Because surface tension decreases with rise in temperature.

Q18. Why does an aldehyde reduce Tollen’s reagent but a ketone does not?
Ans: Aldehydes are easily oxidized to acids, while ketones resist oxidation under mild conditions.

Q19. Why is acetic acid soluble in water but benzene is not?
Ans: Acetic acid forms hydrogen bonds with water, while benzene is non-polar.

Q20. Why is sodium carbonate used to test for phenols?
Ans: Phenols are weak acids and do not react with sodium carbonate, unlike carboxylic acids.

Q21. Why does glucose reduce Fehling’s solution?
Ans: Glucose contains an aldehyde group in its open-chain form, which reduces Cu²⁺ to Cu⁺.

Q22. Why is a flame test used in organic practicals?
Ans: It helps identify aromatic compounds by their sooty flame.

Q23. Why should acids be added to water and not water to acids?
Ans: Adding water to acid causes violent splashing due to heat released, which is dangerous.

Q24. Why are organic solvents not disposed of in sinks?
Ans: They are flammable and may react with other chemicals, causing hazards.

Q25. Why must we avoid inhaling gases evolved during salt analysis?
Ans: Many gases (like H₂S, SO₂, Cl₂) are toxic and harmful to health.

Q26. Why is phenolphthalein colorless in acidic solution but pink in basic solution?
Ans: Because it ionizes in alkaline medium to give a pink-colored anion.

Importance of CBSE Class 12 Chemistry Viva Questions

The viva is an essential component of the Chemistry practical exam. It is not just about memorizing answers but demonstrating conceptual understanding, analytical thinking, and lab awareness. Here’s why viva questions are important:

• Tests Conceptual Clarity: Viva questions assess whether students understand the theory behind experiments.
• Checks Laboratory Skills: They evaluate proper handling of apparatus, chemicals, and observation techniques.
• Boosts Confidence: Regular practice of viva questions improves students’ confidence to answer spontaneously in front of examiners.
• Enhances Problem-Solving Skills: Students learn to explain observations, deviations, and errors logically.
• Improves Accuracy and Safety Awareness: Questions on lab safety and good practices encourage careful and safe experimentation.
• Contributes to Scoring Full Marks: Viva marks are a significant part of practical exams, and preparation can secure high scores.

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