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KEAM 2010 Physics and Chemistry Paper
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© examsnet.com
Question : 119
Total: 119
In Lassaigne's test for the detection of halogens, the sodium fusion extract is first boiled with concentrated nitric acid. This is
to remove silver halides
to decompose
N
a
2
S
and
N
a
C
N
,
if present
to dissolve
A
g
2
S
to dissolve AgCN, if formed
because
A
g
2
S
and
A
g
C
N
are insoluble in nitric acid
Validate
Solution:
To test halogens, it is necessary to remove sodium cyanide and sodium sulphide from the sodium extract, if
N
and
S
are present. This is done by boiling sodium extract with conc
H
N
O
3
.
N
a
C
N
+
H
N
O
3
⟶
N
a
N
O
3
+
H
C
N
↑
N
a
2
S
+
2
H
N
O
3
⟶
2
N
a
N
O
3
+
H
2
S
↑
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