Class 12 Chemistry Practical Viva Questions and Answers

For a Class 12 Chemistry practical viva, start with the experiment in front of you. You should be able to explain what you measured, why a reagent was used and how you recognised the result. A memorised answer becomes fragile when the examiner changes one detail.

This revision guide uses the CBSE Chemistry curriculum for 2026-27 and the NCERT laboratory manual on redox titration. The questions below are practice prompts, not an official question bank or a prediction. Revise the experiments actually taught in your school.

Know where the viva fits

The regular Class XII practical evaluation totals 30 marks: volumetric analysis 8, salt analysis 8, a content-based experiment 6, project work 4, and class record and viva together 4. Do not describe the last four marks as a separate four-mark viva. The curriculum also has a separate assessment scheme for visually impaired students; do not mix those allocations with the regular scheme.

For practical scheduling rather than revision questions, see our CBSE practical exam date guide. Confirm your own reporting time and instructions with your school.

Titration answers worth understanding

1. What does a titration determine? It can determine an unknown solution's concentration by measuring the volume that reacts with a solution of known concentration. Name the actual solutions in your experiment rather than stopping at the definition.

2. Why rinse the burette and pipette with their respective solutions? Water left inside can dilute those solutions. Use the solution intended for each apparatus. This is different from cleaning the glassware before use.

3. Why not rinse the conical flask with the experimental solution? It would add an unmeasured amount of reacting substance. A clean flask can contain distilled water: that changes dilution, not the amount of substance delivered by the pipette. The warning is about rinsing with the reacting solution, not a ban on washing the flask.

4. Why remove an air bubble from the burette tip? Liquid used to fill that space can appear in the burette-volume change without reaching the flask. The recorded delivery would then be misleading. Also remove the funnel before the initial reading so later drops cannot alter it.

5. Why is potassium permanganate a self-indicator? In the acidic titration, its colour disappears while reducing agent remains. A small excess produces the permanent light pink endpoint. No separate indicator is needed for this experiment.

6. Why use dilute sulphuric acid? The reaction needs an acidic medium. Nitric acid is itself an oxidising agent; hydrochloric acid can react with permanganate and produce chlorine. These are reasons for the specified reagent, not an invitation to try alternatives.

7. Why warm oxalic acid, but not Mohr's salt solution? NCERT specifies warming the oxalic-acid and sulphuric-acid mixture to 50-60 degrees Celsius for that titration. The Mohr's salt reaction is fast at room temperature; heating is not required. Do not carry a precaution from one experiment into another automatically.

8. Which meniscus is read here? NCERT specifies the upper meniscus for the dark potassium permanganate solution. Identify the solution before answering. Saying “always lower meniscus” ignores the actual experiment.

Explain observations without guessing

9. What is the difference between an observation and an inference? “A precipitate appeared” records something seen. Naming an ion is an interpretation that needs the prescribed supporting tests. In salt analysis, explain your actual sequence and confirmatory evidence rather than declaring an ion from colour alone.

10. What is qualitative salt analysis? It identifies the ions present, rather than measuring their quantity. The current curriculum specifies determining one anion and one cation in a given salt and excludes insoluble salts. Use your school's approved scheme; this article is not a procedure for handling reagents at home.

11. What should you know about your project? Explain its question, the method you actually used and what your observations support. If a result was uncertain, say why. Do not claim you measured something merely because it appears in a downloaded project.

12. How would you explain an inconsistent reading? Name a possible error tied to the apparatus or step, such as an unnoticed burette-tip bubble. Then explain its effect. “Human error” alone says little, and an unusual reading should not be silently rewritten.

Rehearse from your own record

Open one completed experiment and cover the explanation. Say the aim aloud, identify each solution and explain one precaution. Ask a teacher or study partner to change the question: would the same explanation apply to a different solution?

Mark answers you cannot explain and return to the relevant manual section. For help working through those gaps, explore Class 12 tuition. Keep wet-laboratory practice in school under teacher supervision. Never taste chemicals, directly inhale evolved gases or mouth-pipette.

Frequently asked questions

Is the Chemistry viva alone worth four marks?

No. The regular CBSE 2026-27 scheme assigns four marks to class record and viva together.

Are these guaranteed board viva questions?

No. They are practice prompts based on curriculum topics and NCERT procedures, not predictions.

Must every permanganate titration be heated?

No. NCERT warms the oxalic-acid mixture but does not require heating the Mohr's salt solution.

Can I practise these experiments at home?

Revise explanations at home. Handle chemicals and perform experiments only in an approved supervised laboratory.