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Question
Chemistry
The brown ring test for nitrates depends on
Q. The brown ring test for nitrates depends on
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CMC Medical
CMC Medical 2009
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A
the reduction of nitrate to nitric oxide
B
oxidation of nitric oxide to nitrogen dioxide
C
reduction of ferrous sulphate to iron
D
oxidising action of sulphuric acid
Solution:
The brown ring is obtained due to the formation of pentaaquanitrosonium ion. In this reaction reduction of nitrate ion by
F
e
2
+
ion takes places as
N
O
3
−
+
3
F
e
2
+
+
4
H
+
NO
+
3
F
e
3
+
+
2
H
2
O
F
e
2
+
+
NO
+
5
H
2
O
b
ro
w
n
co
m
pl
e
x
[
F
e
(
H
2
O
)
5
NO
]
2
+