Chemistry Practical – Volumetric Analysis
Get Viva Questions with Answers for Class 12 Chemistry on Infinity Learn for free.
Viva Questions with answers
Question.1.What is a standard solution?
Answer. A solution whose strength is known is called a standard solution.
Question.2.What is a normal solution?
Answer. A solution containing one gram-equivalent mass of the solute per litre of the solution is called a normal solution.
Question.3.What is the equivalent mass of KMnO4 when it acts as the oxidizing agent in an acidic medium?
Answer. KMnO4 loses 5 electrons per molecule when it acts as the oxidizing agent in the presence of acids. Therefore, its equivalent mass is one-fifth of its molecular mass.
Question.4.Is sodium hydroxide a primary standard?
Question.5.Are ‘molality’ and “molarity’’ same?
Answer. No, The number of moles of solute present in 1000 grammes of a solution is defined as molality, whereas molarity refers to the number of moles of solute present per litre of a solution.
Question.6.What would be the normality of 0.10M KMnO4?
Answer. It will be 0.1 x 5 = 0.5 N.
Question.7.What volume of 10M HCl must be diluted with water to get 1L of 1M HCl ?
Question.8.What is the basicity of H2SO4?
Question.9.What is the relationship between normality (N), molarity (M), molecular mass and equivalent mass?
Answer. Normality x Eq. Mass = Molarity x Mol. Mass.
Question.10.Why front door of the balance is closed during weighing?
Answer. Opening the front door causes vibrations in the pan due to the operator’s breath which leads to inaccurate results.
Question.11.What is the maximum weight that can be weighed in a chemical balance?
Question.12.What is the weight of a rider?
Answer. 10 mg.
Question.13.What is the use of a rider?
Answer. A rider is used for weights less than 10 mg.
Question.14. What is the principle of volumetric analysis?
Answer. The concentration of a solution can be determined via volumetric analysis by enabling a known volume of the solution to react quantitatively with another solution of known concentration.
Question.15. What is titration?
Answer. Titration is the process of transferring one solution from the burette to another in the conical flask to complete the chemical reaction.
Question.16. What is an indicator?
Answer. an indicator is a chemical substance that changes colour at the endpoint.
Question.17. What is endpoint ?
Answer. The stage during titration at which the reaction is just complete is known as the endpoint of the titration.
Question.18. Why a titration flask should not be rinsed?
Answer. This is because during rinsing-some liquid will remain sticking to the titration flask therefore the pipetted volume taken in the titration flask will increase.
Question.19. What are primary and secondary standard substances?
Answer. A material is considered a primary standard if it has a high degree of purity, is stable and unaffected by air, does not acquire or lose moisture in the air, is readily soluble, and its solution in water is stable for an extended period of time.
On the other hand, a substance that does not possess the above characteristics is called a secondary standard substance. Primary standards are crystalline oxalic add, anhydrous Na2CO3, Mohr’s salt, etc.
Question.20. Burette and pipette must be rinsed with the solution with which they are filled, why?
Answer. The burette and pipette are rinsed with the solution with which they are filled in order to remove any water sticking to their sides, which otherwise would decrease the cone, of the solutions to be taken in them.
Question.21. It is customary to read lower meniscus in case of colourless and transparent solutions and upper meniscus in case of highly coloured solutions, why?
Answer. Because it is easy to read the lower meniscus in the case of colourless solutions, while the upper meniscus in the case of coloured solutions. In the case of coloured solutions, the lower meniscus is not visible clearly.
Question.22. What is a molar solution?
Answer. A molar solution is a solution, a litre of which contains one gm-mole of the substance. This is symbolised as 1M.
Question.23. Why the last drop of the solution must not be blown out of a pipette?
Answer. Since the drops left in the jet end is extra of the volume measured by the pipette.
Question.24. The pipette should never be held from its bulb, why?
Answer. The body temperature may expand the glass and introduce an error in the measurement volume.
Question.25. What are acidimetry and alkalimetry?
Answer. It is the branch of volumetric analysis involving a chemical reaction between an acid and a base.
Question.26. What is permanganometry ?
Answer. Redox titrations involving KMnO4 as the oxidising agent are called permanganometric titrations.
Question.27. Which are an oxidising agent and a reducing agent in the reaction between KMnO4 and FeSO4?
Answer. KMnO4 acts as an oxidising agent and FeSO4 acts as a reducing agent.
Question.28. What is the indicator used in KMnO4 titration?
Answer. No indicator is used because KMnO4 acts as a self-indicator.
Question.29. Why does KMnO4 act itself as an indicator?
Answer. KMnO4 interacts with the reducing agent in the presence of dilute sulfuric acid (oxalic acid or . ferrous sulphate). When all of the reducing agents has been oxidised, the excess KMnO4 does not break down and gives the solution a pink colour.
Question.30. What is the endpoint in KMnO4 titrations?
Answer. From colourless to permanent light pink.
Question.31. Why is Mohr’s salt preferred as a primary standard over ferrous sulphate in volumetric
Answer. This is because of fact that Mohr’s salt is stable and is not readily oxidised by air. Ferrous sulphate gets oxidised to ferric sulphate.
Question.32. Why are a few drops of dilute sulphuric acid added while preparing a standard solution
of Mohr’s salt?
Answer. Few drops of H2SO4 are added to prevent the hydrolysis of ferrous sulphate.
Question.33. Why a burette with a rubber pinch cock should not be used in KMnO4 titrations?
Answer. Because KMnO4 attacks rubber.
Question.34. Sometimes a brown ppt. is observed in KMnO4 titrations. Why?
Answer. It is due to insufficient quantity of dil. sulphuric acid. Brown coloured ppt. (MnO2.H20) is formed due to the incomplete oxidation of KMnO4.
Question.35. Why should you heat the oxalic acid solution to about 60-70°C before titrating with KMnO4 solution?
Answer. Due to the slow production of Mn2+ ions in freezing temperatures, the process is very slow. The process proceeds quickly because oxalic acid is heated to speed up the liberation of Mn2+ ions, which subsequently autocatalyze the reaction. This also assists to remove the carbon dioxide produced during the process, which would otherwise prevent the reaction from finishing.