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Most important viva-voce questions for Salt Analysis or Qualitative analysis

1. What is qualitative analysis?

Ans. The type of analysis that deals with the methods which are used to determine the constituents of a compound.

2. What is a radical?

Ans. A radical may be defined as an atom or group of atoms which carries charge and behaves as a single unit in chemical reactions.

3. What are acidic and basic radicals?

Ans. Radicals carrying positive charge are called basic radicals and those carrying negative charge are called acidic radicals.

4. What type of bond is present in an inorganic salt?

Ans. Electrovalent bond.

5. Why do inorganic salts ionise when dissolved in water?

Ans. Due to the high dielectric constant of water, the force of attraction holding the two ions in a salt decreases. Thus, the two ions separate. The ions are further stabilized by solvation.

6. Give examples of some coloured basic radicals.

Ans.Cu2+, Fe2+, Fe3+, Cr3+, Ni2+, Co2+ and Mn2+.

7. What is the colour of iron salts?

Ans. Ferrous salts are usually light green while ferric salts are generally brown.

8. Name any iron salt which is light green.

Ans. Ferrous sulphate.

9. What is the colour of nickel salts?

Ans. Bluish green or green.

10. What is the colour of manganese salts?

Ans. Light pink or flesh colour.

11. Name the basic radicals which are absent, if the given salt is white.

Ans. Cu2+, Fe2+, Fe3+, Cr3+, Ni2+, Co2+ and Mn2+.

12.Why a salt containing lead turn black in colour, when placed for a long time in labora-tory?

Ans. Due to the formation of black lead sulphide by the action of H2S in atmosphere.

13. Tell the importance of preliminary tests in qualitative analysis.

Ans. Sometimes, preliminary tests give authentic information about an ion in the salt. For example, golden yellow colour in flame test shows the presence of sodium. In a charcoal cavity test, brown residue shows the presence of cadmium in a salt and so on.

14. What is Nessler’s Reagent?

Ans. It is a solution of mercuric iodide in potassium iodide. Its formula is K2[HgI4].

15. Name the acid radicals detected with dil. H2SO4.

Ans. CO32-, S2-, SO32-, NO2–.

16. Why dil. H2SO4 is preferred while testing acid radicals over dil. HCl?

Ans. When the salt is treated with HCl, during reaction HCl gas is also given out along with the gas evolved by the salt. So the actual gas cannot be identified whereas with H2SO4, no such problem arises.

17. Name the acid radicals detected by cone. H2SO4.

Ans. Cl–, Br–, I–, NO3–, CH3COO–.

18. How is sodium carbonate extract prepared?

Ans. The salt is mixed with double the amount of solid Na2CO3 and about 20 ml of distilled water. It is then boiled till it is reduced to one-third, and then filtered. The filtrate is sodium carbonate extract or (S.E.).

19. CO2 and SO2 both turn lime water milky. How will you distinguish between them?

Ans. By passing through acidified K2Cr2O7 solution. SO2 turns K2Cr2O7 green while CO2 has no effect.

20. How will you test the presence of carbonate?

Ans. Treat a small quantity of the mixture with dil. H2SO4. CO2 gas is evolved. When the gas is passed through lime water, it is turned milky.

21. What is lime water?

Ans. A solution of Ca(OH)2 in water is called lime water.

22. What will happen if excess of CO2 is passed through lime water?

Ans. The white ppt. of CaCO3 changes into soluble calcium bicarbonate and the milkiness, therefore, disappears.

23. What is Tollen’s reagent?

Ans. Ammonical AgNO3 solution is called Tollen’s reagent.

24. What is the formula of Sodium nitroprusside?

Ans. Na2[Fe(CN)5 NO].

25. What is aqua regia?

Ans. Aqua regia is a mixture of concentrated HCl and concentrated HNO3 in the ratio 3:1 by volume.

26. Name group reagents for different groups.

Ans. Group I—Dil. HCl.

Group II—H2S in the presence of dil. HCl.

Group III—NH4OH in presence of NH4Cl.

Group IV—H2S in presence of NH4OH.

Group V—(NH4)2 CO3 in presence of NH4Cl and NH4OH.

Group VI—No specific group reagent.

27. What is blue lake?

Ans. It is blue particles, blue litmus adsorbed on white ppt. of Al(OH)3, floating in colourless solution

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