Qualitative Analysis (Detection of Nitrogen, Sulphur, Phosphorus, and Halogens ) NEET Questions

Organic Chemistry - Purification and Characterization of Organic Compounds

Qualitative Analysis (Detection of Nitrogen, Sulphur, Phosphorus, and Halogens ) MCQ Questions


7.
In Lassaigne's test for nitrogen, the appearance of which colour confirms the presence of nitrogen?
A.
Blood red
B.
Black
C.
Prussian blue (or green)
D.
Violet
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ANSWER :
C. Prussian blue (or green)
8.
In the test for nitrogen, the sodium fusion extract is boiled with FeSO₄ and then acidified with concentrated H₂SO₄. The Prussian blue compound formed is:
A.
Na₄[Fe(CN)₆]
B.
Fe₄[Fe(CN)₆]₃
C.
Fe₃[Fe(CN)₆]₄
D.
Fe₂[Fe(CN)₆]
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ANSWER :
B. Fe₄[Fe(CN)₆]₃
9.
Why is concentrated H₂SO₄ added during the test for nitrogen in Lassaigne's test?
A.
To liberate HCN gas
B.
To reduce Fe³⁺ to Fe²⁺
C.
To precipitate iron sulphide
D.
To dissolve the precipitate of NaOH and oxidize some Fe²⁺ to Fe³⁺ which is required for Prussian blue formation
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ANSWER :
D. To dissolve the precipitate of NaOH and oxidize some Fe²⁺ to Fe³⁺ which is required for Prussian blue formation
10.
The first step in the formation of Prussian blue colour in the test for nitrogen is the formation of:
A.
Sodium hexacyanidoferrate(II), Na₄[Fe(CN)₆]
B.
Fe₂(CN)₆
C.
Fe(CN)₃
D.
NaFe(CN)₂
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ANSWER :
A. Sodium hexacyanidoferrate(II), Na₄[Fe(CN)₆]
11.
When sodium fusion extract of a sulphur-containing organic compound is treated with lead acetate after acidification with acetic acid, the colour of the precipitate is:
A.
Black
B.
Yellow
C.
White
D.
Brown
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ANSWER :
A. Black
12.
The violet colour produced when sodium fusion extract is treated with sodium nitroprusside indicates the presence of:
A.
Nitrogen
B.
Halogens
C.
Sulphur
D.
Phosphorus
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ANSWER :
C. Sulphur