Environmental Engineering Reference
In-Depth Information
(a) Cr
N
N
H
H
R
C
+ Cr
6+
2
N
N
H
Cr
O
8.16
N
O
CR
N
C
NN
H H
H
O
1,5-diphenylcarbohydrazide
(b) CN
2CN
-
+ Cl
2
2CNCl
8.17
CNCl +
+ Cl
-
8.18
N
N
+
CN
H
O
C
+ Cl
-
CCCCO
4H
2
O +
+ 2NH
3
+ CO
2
+ HCl
8.19
N
+
CN
H
H
H
H
H
H
O
H
H
H
H
O
O
C
CCCC
O
+ 2H
2
O
+ 2
N
C
CCCC
N
N
O
H
H
H
H
H
H
H
N
N
N
8.20
CH
3
CH
3
H
3
C
(c) Phenol
OH
8.21
H
3
C
N
O
H
3
C
N
O
+
N
N
H
3
C
N
O
H
3
C
NH
2
4-Aminiantipyrine
(d) P
12MoO
3
+ H
2
PO
4
-
(H
2
PMo
12
O
40
)
-
(H
2
PMo
12
O
40
)
-
+ ascorbic acid (or amino acid) molybdenum blue
8.22
8.23
(e) Si
H
2
SiO
3
+ 3H
2
O H
8
SiO
6
H
8
SiO
6
+ 12(NH
4
)
2
MoO
4
+ 12H
2
SO
4
H
8
[Si(Mo
2
O
7
)
6
] + 12(NH
4
)
2
SO
4
+ 12H
2
O
H
8
[Si(Mo
2
O
7
)
6
] (silicomolybdic acid; faint yellow) + amino acid Heteropoly Blue
8.24
8.25
8.26
(f) S
NH
2
N
+ 2H
2
S + Cr
2
O
7
2-
+ 10H
+
+ 2Cr
3+
+ 2NH
4
+
+ 7H
2
O
4
8.27
2
(H
3
C)
2
N
N(H
3
C)
2
S
N(CH
3
)
2
N
,
N
-dimethyl-
p
-phenylenediamine
Methylene blue
Figure 8.16
Reaction mechanisms for the spectrometric measurement of (a) chromium (Cr): Eq. 8.16,
(b) cyanide (CN
-
): Eqs 8.17 to 8.20, (c) phenol: Eq. 8.21, (d) phosphate: Eqs 8.22 to 23, (e) silicon (Si):
Eqs 24 to 26, (f) sulfide (S
2
): Eqs 8.27
Light source
: A typical infrared source is the Nernst glower. This is a
rod consisting of a mixture of rare-earth oxides, which is heated to
1500-2000
C to emit the radiation. Another infrared source is the
Globar, consisting of a rod made of sintered silicon carbide (SiC),
which is heated to about 1300-1700
C.
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