Qualitative and Quantitative Analysis (Estimation of Carbon, Hydrogen, Nitrogen,... ) NEET Questions

Organic Chemistry - Purification and Characterization of Organic Compounds

Qualitative and Quantitative Analysis (Estimation of Carbon, Hydrogen, Nitrogen,... ) MCQ Questions


7.
In Lassaigne's test for nitrogen, the Prussian blue colour is due to the formation of:
A.
Na4[Fe(CN)6]
B.
Fe3[Fe(CN)6]4
C.
Fe2[Fe(CN)6]
D.
Fe4[Fe(CN)6]3
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ANSWER :
D. Fe4[Fe(CN)6]3
8.
In the test for nitrogen by Lassaigne's method, FeSO4 is added to the sodium fusion extract followed by:
A.
Conc. HNO3
B.
Conc. H2SO4
C.
Conc. HCl
D.
Acetic acid
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ANSWER :
B. Conc. H2SO4
9.
When both N and S are present in an organic compound, Lassaigne's test gives:
A.
Prussian blue colour
B.
Black precipitate
C.
Blood red colour due to Fe(SCN)³⁺
D.
Yellow precipitate
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ANSWER :
C. Blood red colour due to Fe(SCN)³⁺
10.
If sodium fusion is carried out with excess of sodium when both N and S are present, the test gives:
A.
Prussian blue colour (separate tests for N and S)
B.
Blood red colour only
C.
No colour
D.
Yellow precipitate
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ANSWER :
A. Prussian blue colour (separate tests for N and S)
11.
In Lassaigne's test for sulphur, addition of lead acetate to the acidified sodium extract gives:
A.
Black precipitate of PbS
B.
White precipitate of PbS
C.
Yellow precipitate of PbS
D.
Brown precipitate of PbS
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ANSWER :
A. Black precipitate of PbS
12.
Sodium nitroprusside test for sulphur in Lassaigne's extract gives a colour:
A.
Blood red
B.
Prussian blue
C.
Violet/Purple
D.
Yellow
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ANSWER :
C. Violet/Purple