Page 80 - Chemistry - XI

Q30. Why is it necessary to add few drops of conc. HNO before proceeding to group III if salt is
3
coloured?
Ans. It is used to convert Fe ions to Fe ions. Fe ions are not completely precipitated in group III and
2+
3+
2+
may get precipitated in group IV as FeS which interfaces in the regular scheme of analysis.
Q31. Name sulphide of basic radicals which are soluble in aqua regia.
Ans. HgS,CoS, NiS are soluble in aqua regia.

Q32. What is solubility product?
Ans. It is defi ned as product of molar concentration of ions of sparingly soluble salt in saturated solution
raised to the power the number of ions produced per formula of the compound, e.g.

PbCl  Pb +2Cl −
2+
2
K= Pb Cl 2

2+
sp
Q33. What is the need of preparing ʻoriginal solutionʼ of given salt for basic radicals?
Ans. It is because the tests of basic radicals are done in aqueous solution.
Q34. Can we use NH NO in place of NH Cl in group III?
3
4
4
Ans. Yes, because we need NH which gives NH NO in aqueous solution.
+
4 4 3
Q35. Explain why conc. HNO cannot be used to acidify the solution in place of HCl in second group
3
before passing H S gas?
2
Ans. Conc. HNO is good oxidising agent, it will oxidise H S to colloidal sulphur.
2
3
Q36. What is common ion eff ect?
Ans. The decrease in concentration of one of the ions by adding other ion as common ion is called
common ion eff ect.

Q37. NH OH is added before the addition of (NH ) CO solution in group V, why?
4
3
4 2
Ans. K of carbonate of group V radicals is low, therefore, less concentration of Co is required. NH is
2−
+
sp 3 4
being added as common ion so as to decrease concentration of Co which is suffi cient to precipitate
2−
3
group V radicals, but not group VI (Mg ).
2+
Q38. Wet tests are generally done with sodium carbonate extract. Explain when do we prepare soda
extract?
Ans. It is because most of the salts of sodium are soluble in water. It is prepared when salt is insoluble in
water.
Q39. Why are sodium, potassium, and NH not precipitated in any of the group I to VI?
+
4
Ans. The salts of Na , K , and NH are highly soluble in water, therefore, they cannot be precipitated.
+
+
+
4
Q40. How do you clean a glass apparatus?

Ans. They are cleaned by HNO (conc.) or chromic acid KCrO +conc. HSO .
3 2 2 7 2 4
Q41. What is Chromyl chloride test? Why do Br or I not respond to this test? Give chemistry of
–
–
Chr
Chromyl chloride test.omyl chloride test.
Ans. Take a little amount of salt in a test tube and add to it an equal amount of solid K Cr O . Add conc. Take a little amount of salt in a test tube and add to it an equal amount of solid K
Ans. 2 2 7
H
H SO to the same test tube and heat it. Pass the gas in NaOH solution. Yellow colouration is SO 4 4
2 2
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