Chemistry practical exams are a crucial part of the CBSE Class 12 curriculum. A strong preparation for viva questions can boost your confidence and performance. Here are 50 essential viva questions and answers to help you excel in your Class 12 Chemistry practical exam for the 2024-25 academic session.
General Questions
- What is the purpose of a practical exam in Chemistry?
- To apply theoretical knowledge practically and develop experimental skills.
- What safety precautions should you follow in a chemistry lab?
- Wear lab coats and safety goggles, handle chemicals carefully, and avoid eating or drinking in the lab.
- Why is it important to record observations accurately?
- Accurate observations ensure the validity and reliability of experimental results.
- What is the difference between qualitative and quantitative analysis?
- Qualitative analysis identifies the components, while quantitative analysis measures their quantities.
Physical Chemistry Questions
- What is molarity?
- Molarity is the number of moles of solute per liter of solution.
- Define normality.
- Normality is the number of gram equivalents of solute per liter of solution.
- How do you determine the boiling point of a liquid?
- By heating the liquid in a boiling tube and noting the temperature at which it boils steadily.
- What is osmosis?
- The movement of solvent molecules from a region of lower concentration to higher concentration through a semi-permeable membrane.
- What is the principle of conductometric titration?
- It measures the change in electrical conductivity of a solution during a chemical reaction.
Organic Chemistry Questions
- What is esterification?
- A reaction between an alcohol and a carboxylic acid to form an ester and water.
- How do you test for the presence of phenol?
- By adding neutral FeCl₃; it gives a violet coloration.
- What is the iodoform test?
- A test for the presence of methyl ketones; it produces a yellow precipitate of iodoform.
- Why is ethanol considered a versatile solvent?
- It can dissolve both polar and non-polar substances.
- How do you identify a carboxylic acid in the lab?
- By its reaction with sodium bicarbonate, which produces CO₂ gas.
Inorganic Chemistry Questions
- What is the principle behind salt analysis?
- It involves systematic qualitative analysis to identify the cations and anions in a salt.
- How do you confirm the presence of chloride ions?
- By adding AgNO₃, which forms a white precipitate of AgCl.
- What happens when ammonia reacts with CuSO₄?
- It forms a deep blue-colored complex, [Cu(NH₃)₄]SO₄.
- What is a precipitation reaction?
- A reaction in which an insoluble solid (precipitate) is formed.
- How can you differentiate between Zn²⁺ and Al³⁺ ions?
- By adding NaOH; Zn²⁺ gives a soluble white precipitate, while Al³⁺ gives an insoluble white precipitate.
Practical-Based Questions
- What is the principle of volumetric analysis?
- It is based on the measurement of the volume of a solution of known concentration required to react with the analyte.
- How do you prepare a standard solution?
- By dissolving a known weight of solute in distilled water and making up the solution to a specific volume.
- What is a titration?
- A technique to determine the concentration of an unknown solution using a solution of known concentration.
- Why is a burette used in titration?
- It allows precise measurement of the volume of a solution.
- What is the end point in a titration?
- The point at which the reaction is complete, often indicated by a color change.
- Why is phenolphthalein used as an indicator?
- It changes color in the pH range of 8.2 to 10, making it suitable for acid-base titrations.
- What is the role of an indicator in a titration?
- To show the completion of the reaction by a visible color change.
Advanced Questions
- What is the difference between primary and secondary standards?
- Primary standards are pure and stable; secondary standards are standardized against primary standards.
- What is the pH of a neutral solution?
- 7.
- How does temperature affect the rate of reaction?
- An increase in temperature generally increases the rate of reaction.
- What is the Nernst equation?
- It relates the reduction potential of an electrochemical cell to the standard electrode potential, temperature, and activities of the chemical species involved.
- What are colligative properties?
- Properties of solutions that depend on the number of solute particles, not their nature (e.g., boiling point elevation, freezing point depression).
Miscellaneous Questions
- What is the function of a desiccator?
- To keep substances dry by absorbing moisture.
- Why is distilled water used in experiments?
- To avoid impurities that could interfere with the results.
- What is the role of a catalyst?
- To speed up the reaction without being consumed.
- Define equilibrium constant.
- The ratio of the concentration of products to reactants, each raised to their stoichiometric coefficients, at equilibrium.
- What is the difference between endothermic and exothermic reactions?
- Endothermic reactions absorb heat; exothermic reactions release heat.
Salt Analysis Questions
- How do you test for carbonate ions?
- By adding dilute acid; it produces effervescence due to CO₂ gas.
- What is the confirmatory test for sulfate ions?
- Adding BaCl₂, which forms a white precipitate of BaSO₄.
- How do you detect nitrate ions?
- By the brown ring test.
- What happens when Fe³⁺ reacts with thiocyanate?
- It forms a blood-red complex, [Fe(SCN)]³⁺.
Practical Tips
- Why is it necessary to swirl the conical flask during titration?
- To mix the solutions thoroughly.
- What is the use of a pipette in titration?
- To measure a fixed volume of solution accurately.
- Why should air bubbles be removed from the burette?
- To avoid errors in volume measurement.
- What is the purpose of calibrating instruments?
- To ensure accurate and reliable measurements.
- Why is a control experiment important?
- To compare results and validate the experiment.
Additional Questions
- What is chromatography?
- A technique for separating and analyzing components of a mixture.
- Why is KMnO₄ a self-indicator?
- Because it changes color during the reaction.
- What is the significance of Rf value in chromatography?
- It indicates the relative distance traveled by a compound compared to the solvent.
- How do you handle volatile chemicals safely?
- Work in a well-ventilated area and use fume hoods if necessary.
- What is the purpose of drying the precipitate in gravimetric analysis?
- To ensure accurate weighing by removing moisture.
By mastering these questions and answers, you can face your Chemistry practical viva with confidence. Practice well, stay calm, and all the best for your exam!
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