CBSE Class 12 Chemistry Viva Questions with Answers 2023-24

CBSE Class 12 Chemistry Viva Questions with Answers 2023-24 helps the students to have several questions to practise before appearing for the Chemistry practical viva voce. These are conceptual questions that require the students to have a good understanding of the chapters.

The questions asked in the viva voce for CBSE 12th board exams are based on the experiments performed in the practical examination. The viva consists of 4 marks and students must thoroughly prepare the answers to score full marks in the viva. Viva voce communicates the students’ understanding of the topic and the experiment.

CBSE Class 12 Chemistry Viva-Voce Questions with Answers 2023-24

The most asked questions in the chemistry practical viva voce along with the answers are given below. The students must refer to these while preparing for the examination.

1. What is meant by a standard solution?

Answer: A solution whose strength is known can be called a standard solution.

2. What is the difference between molality and molarity?

Answer: The molality of a solution is the number of moles of a solute present in 1000 grams of the solution. However, the molarity of a solution is the number of moles of the solute present in each 1 litre of the solution.

3. Is sodium hydroxide a primary standard?

Answer: No, sodium hydroxide is not a primary standard. It is a secondary standard.

4. What is the equivalent mass of KMnO4 when it acts as an oxidising agent in an acidic medium?

Answer: KMnO4 loses 5 electrons per molecule when it acts as an oxidising agent in the presence of acids. Its equivalent mass is one-fifth of the molecular mass of the compound.

5. What is a normal solution?

Answer: A solution which contains 1 gram-equivalent mass of the solute per litre of the solution is known as a normal solution.

6. Why is the front door of the balance closed at the time of weighing?

Answer: The front door is closed because if the front door is open it causes the pan to vibrate due to the breath of the operator that causes the result to be inaccurate.

7. What is the relationship between normality (N), molarity (M), molecular mass and equivalent mass?

Answer: Normality x Equivalent Mass = Molarity x Molecular Mass.

8. What is the basicity of H2SO4?

Answer: 2

9. What volume of 10M HCl must be diluted with water to get 1 litre of 1M HCl?

Answer: 0.1 litre

10. What will be the normality of 0.10M KMnO4?

Answer: The normality will be (0.1 x 5 =) 0.5 N.

11. What is titration?

Answer: The process of adding one solution from a burette to a solution in a conical flask to allow a chemical reaction to take place is called titration.

12. What is the principle of volumetric analysis?

Answer: In volumetric analysis, the concentration of a solution is obtained by allowing a known volume of a solution to quantitatively react with a solution of a known concentration.

13. What is the use of a rider?

Answer: A rider is used to weigh objects with a mass of less than 10 mg.

14. What is the weight of a rider?

Answer: 10 mg.

15. What is the maximum weight which can be weighed in a chemical balance?

Answer: 100 grams.

16. Why must the Burette and pipette be rinsed with the solution with which they are filled?

Answer: The burette and pipette are rinsed with the solution with which they are filled to remove any excess water sticking to the sides, which would cause the cone to decrease.

17. What are primary and secondary standard substances?

Answer: A substance can be called a primary standard if it is available in a high degree of purity, if it does not gain or lose moisture in air, if it is stable and unaffected by air, if it soluble and the solution in water remains as such for a long time.

Any substance that does not have the above mentioned characteristics is known as a secondary standard substance.

18. Why must you not rinse a titration flask?

Answer: A titration flask must not be rinsed because during rinsing amount of the liquid will stick to the titration flask which will increase the pipetted volume in the titration flask.

19. What is the endpoint?

Answer: The stage of titration when the reaction is complete is called the end point of titration.

20. What is an indicator?

Answer: An indicator is a chemical substance which changes colour at the endpoint.

21. Why should the oxalic acid solution be heated to around 60-70°C before titrating it with KMnO4 solution?

Answer: The reaction is slow in cold due to the slow formation of Mn2+ ions. Oxalic acid is heated to accelerate the release of the Mn2+ ions. This catalyses the reaction. This also expels the carbon dioxide evolved during the chemical reaction which if not removed will not allow the reaction to complete.

22. Why must a burette with a rubber pinch cock not be used in KMnO4 titrations?

Answer: The reason is that KMnO4 reacts with rubber.

23. What is the brown precipitate observed in KMnO4 titrations?

Answer: The brown precipitate (MnO2.H20) is formed due to the incomplete oxidation of KMnO4.

24. Why is Mohr’s salt preferred to ferrous sulphate as a primary standard in volumetric analysis?

Answer: Mohr’s salt is stable and does not get readily oxidised by air. Ferrous sulphate is oxidised to ferric sulphate.

25. Why are few drops of dilute H2SO4 added when preparing a standard Mohr’s salt solution?

Answer: Few drops of H2SO4 are added while preparing a standard Mohr's salt solution to prevent the hydrolysis of ferrous sulphate.

26. Why does KMnO4 act as an indicator?

Answer: In the presence of dil. H2SO4, KMnO4 reacts with the reducing agent (ferrous sulphate or oxalic acid). When the reducing agent is oxidised the excess amount of KMnO4 does not get decomposed and imparts a pink colour to the solution, thus acting as an indicator.

27. What is the endpoint in KMnO4 titration?

Answer: The solution becomes permanent light pink to colourless.

28. Name the oxidising agent and the reducing agent in the reaction between KMnO4 and FeSO4.

Answer: KMnO4 is the oxidising agent and FeSO4 is the reducing agent.

29. Which indicator is used in KMnO4 titration?

Answer: No other indicator is used because KMnO4 itself acts as an indicator.

30. Why must a pipette never be held from the bulb?

Answer: It is because the body temperature may expand the glass causing error in volume measurement.

31. What is permanganometry?

Answer: A redox titration that involves KMnO4 as the oxidising agent is known as permanganometric titration.

32. What is a molar solution?

Answer: A litre of a molar solution contains 1 gm-mole of the substance. The symbol is 1M.

33. Why must the last drop of solution not be blown out of the pipette?

Answer: This is because the drops that are left in the jet end is in excess of the volume that is measured by the pipette.

34. Why is the lower meniscus reading taken for colourless and transparent solutions while the higher meniscus reading is taken for the highly coloured solutions?

Answer: This is because it is easier to read the lower meniscus for colourless solutions, whereas the higher meniscus for the coloured solutions. For coloured solutions the lower meniscus is not clearly visible.

Also, Check: CBSE Class 12 Chemistry Paper Analysis 2023

CBSE Class 12 Chemistry Viva Questions with Answers 2023-24: Marks Distribution

The distribution of marks for the Chemistry practical and viva voce questions have been shared below:

Also Check: CBSE Class 12 Previous Year Question Papers

CBSE Class 12 Chemistry Viva Questions with Answers 2023-24: Prescribed Books

The books that can be followed for CBSE class 12 Chemistry practical viva voce are:

1. Chemistry Lab Manual Class 12 |Viva-voce Questions|Lab Experiments|Investigatory Projects| with latest Syllabus prescribed by CBSE
2. CBSE Laboratory Manual Chemistry Class 12th [Experiments|Projects|Viva-Voce](English, Paperback, Arihant Experts)

Also, Check: CBSE Class 12 Chemistry Paper Answer Key 2023

CBSE Class 12 Chemistry Viva Questions with Answers 2023-24: Preparation Tips

The students who are about to appear for CBSE class 12 board examination must abide by the following preparation tips for Chemistry practical viva voce 2023-24:

• Memorising the questions and answers

It is important to have a good knowledge of the concepts of the experiment. This is because the questions are asked based on the experiments.

• Knowing Exceptions

Exceptions are mostly asked in vivas. So, it is crucial to know the exceptions of every law in chemistry.

• Confidence is the key

The students must have confidence in themselves. They must not get nervous. They must understand that nervousness can affect their performance and thereby affect their overall scores in the exam.

• Work on weaknesses

It is crucial to know, understand and address the weaknesses. The practice questions for viva voce that are available here can be referred while practising the questions. This will help the students be aware of the type of questions asked in the viva voce.

• Choose the experiments carefully

The choice of experiments from among the options given must be done carefully. While choosing the experiments, the students must also keep in mind that they will be questioned on the experiments. Thus, it would be prudent to choose such an experiment that they are comfortable with.

Also, Check: CBSE Class 12 Chemistry Deleted Syllabus 2023-24