Chemistry Class 12th Practical Viva Questions with Answers in English Medium

Chemistry practical Examination


Ques: Why is heating done for Oxalic Acid, KMnO4 titration?

Ans: Oxalic acid is heated before titration with KMnO4 solution because this reaction happens only in certain temperature. If not heated your light pink titrated solution turns brown soon & reaction takes longer times but overheating will cause decomposition of oxalic acid as CO2.

Ques: Why is H2SO4 used instead of HCl?

Ans: Sulphuric acid H2SO4 is a colourless (when pure) to dark brown, oily liquid. Why H2SO4 is used instead of HCl? Sulfuric acid is used because it is stable towards oxidation; whereas, for example, hydrochloric acid would be oxidized to chlorine by permanganate.

Ques: Explain the principle of Salt analysis.

Ans: Salt analysis (also known as systematic qualitative analysis or qualitative inorganic analysis) involves the identification of the cation and anion of an inorganic salt. This is done by conducting a series of tests in a systematic manner and using the observations to confirm the absence or presence of specific cations and anions.

Ques: What examples of salt with Colours?


For example:

  • sodium chromate is yellow by virtue of the chromate ion
  • potassium dichromate is orange by virtue of the dichromate ion
  • cobalt nitrate is red owing to the chromophore of hydrated cobalt (II) ( [Co (H 2 O) 6] 2+ ).
  • copper sulfate is blue because of the copper (II) chromophore

Ques: Why are salts classified into groups?

Ans: Salt is formed as a result of neutralisation reaction ( neutralisation reaction is a chemical reaction in which acids and bases cancel the effect of each).

Ques: What is Importance of Flame Test?

Flame tests are useful because gas excitations produce a signature line emission spectrum for an element. When the atoms of a gas or vapor are excited, for instance by heating or by applying an electrical field, their electrons are able to move from their ground state to higher energy levels.

Ques: Why is HCl used in Flame Test?

Ans: In a flame test, concentrated HCl is used to convert the compounds into their metallic chlorides. This is because the metallic chlorides are very much volatile and can easily impart colour to the flame.

Ques: Explain the role of Group 3 reagents.

Ans: In the third group of qualitative analysis, the precipitating reagent is NH4Cl + NH4

OH. The function of NH4Cl is to Classes.

Ques: What is Common Ion effect?

Ans: The common ion effect is an effect that suppresses the ionization of an electrolyte when another electrolyte (which contains an ion which is also present in the first electrolyte, i.e. a common ion) is added.

Ques: What is Formula of Potash Alum, Mohr’s Salt?

Ans: Potash alum – K2SO4.Al2 (SO4)3.24H2O

According to syllabus.

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