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XXVI
Release 05/04
Instructions for the Preparation of Standard Solutions
Standard solution of sulfide
Preparation of a stock solution:
Dissolve 7.2 g of glass-clear, if necessary washed
crystals of sodium sulfide hydrate approx. 35 %
GR with distilled water in a calibrated or conformi-
ty-checked 1000-ml volumetric flask and make up
to the mark with distilled. The stock solution
prepared according to this procedure has a
concentration of approx. 1000 mg/l sulfide.
▼
Precise assay of the standard solution (stock
solution) for sulfide:
Place 100 ml of distilled water and 5 ml (full
pipette) of sulfuric acid 25 % GR in a 500-ml
ground-glass conical flask. To this solution add
25.0 ml (full pipette) of the sulfide stock solution
of approx. 1000 mg/l and 25.0 ml (full pipette) of
iodine solution 0.05 mol/l. Shake the contents
of the flask thoroughly for about one minute, sub-
sequently titrate with sodium thiosulfate solution
0.1 mol/l until the yellow iodine colour has
disappeared, add 1 ml of zinc iodide-starch
solution, and continue to titrate until a milky,
pure white colour emerges.
▼
Calculation of the exact content of the sulfide
solution:
C1 = consumption of sodium thiosulfate 0.1 mol/l
C2 = quantity of iodine solution 0.05 mol/l (25.0 ml)
mg/l sulfide = (C2 – C1)
x
64,1026
Further investigational concentrations may be pre-
pared from the stock solution exactly determined
according to the procedure described above by
diluting accordingly.
▼
Stability:
When stored in a cool place (refrigerator), the
stock solution remains stable for at most one day.
The diluted investigational solutions must be used
immediately.
▼
Reagents required:
1.09099.1000 Iodine solution 0.05 mol
I2/l 0.1 N solution
1.06638.0250 Sodium sulfide hydrate approx.
35 % GR for analysis
1.09147.1000 Sodium thiosulfate solution
0.1 mol/l 0.1 N solution
1.00716.1000 Sulfuric acid 25 % GR for analysis
1.05445.0500 Zinc iodide-starch solution GR
for analysis
1.16754.9010 Water GR for analysis
Standard solution of phenol
Preparation of a standard solution:
Dissolve 1.00 g of phenol GR with distilled water
in a calibrated or conformity-checked 1000-ml
volumetric flask and make up to the mark with
distilled water. The stock solution prepared
according to this procedure has a concentration
of 1000 mg/l phenol.
Further investigational concentrations may be
prepared from this stock solution by diluting
accordingly.
▼
Stability:
When stored in a cool place (refrigerator), the
stock solution remains stable for one week. The
diluted investigational solutions must be used
immediately.
▼
Reagents required:
1.00206.0250 Phenol GR for analysis
1.16754.9010 Water GR for analysis
Standard solution of sodium
Preparation of a standard solution:
A chloride standard solution of 1000 mg/l is used.
1000 mg/l chloride corresponds to 649 mg/l
sodium.
Further investigational concentrations may be
prepared from this stock solution by diluting
accordingly.
▼
Stability:
When stored in a cool place (refrigerator), the
diluted investigational solutions remain stable
for one month.
▼
Reagents required:
1.19897.0500 Chloride standard solution
CertiPur
®
1.16754.9010 Water GR for analysis