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Instructions for the Preparation of Standard Solutions
Standard solution of free chlorine
Preparation of a stock solution of free chlorine:
First prepare a 1:10 dilution using a sodium hypo-
chlorite solution containing approximately 13 % of
active chlorine. For this pipette 10 ml of sodium
hypochlorite solution into a calibrated or confor-
mity-checked 100 ml volumetric flask and then
make up to the mark with distilled water.
Precise assay of the stock solution for free
chlorine:
Pipette 10.0 ml of the stock solution into a 250 ml
ground-glass-stoppered conical flask containing
60 ml of distilled water. Subsequently add to this
solution 5 ml of hydrochloric acid 25% GR. and
3 g of potassium iodide. Close the conical flask
with the ground-glass stopper, mix thoroughly,
and leave to stand for 5 min.
Titrate the eliminated iodine with sodium thiosul-
fate solution 0.1 mol/l until a weakly yellow colour
emerges. Add 2 ml of zinc iodide-starch solution
and titrate from blue to colourless.
Calculation:
1 ml sodium thiosulfate solution = 3.55 mg free
chlorine
Further investigational concentrations may be pre-
pared from the stock solution prepared according
to the procedure described above by diluting
accordingly.
Stability:
When stored in a cool place (refrigerator), the
stock solution remains stable for approximately
one week. The diluted investigational solutions
are stable for approximately 2 hours.
Reagents required:
1.00316.1000 Hydrochloric acid 25 % GR
for analysis
1.05614.9025 Sodium hypochlor. solution techn.
approx. 13 % active chlorine
1.09147.1000 Sodium thiosulfate solution
0.1 mol/l 0.1 N solution
1.05043.0250 Potassium iodide GR for analysis
1.05445.0500 Zinc iodide-starch solution GR
for analysis
1.16754.9010 Water GR for analysis
Release 05/04
Standard solution of free chlorine
Preparation of a standard solution:
Dissolve 1.85 g of dichloroisocyanuric acid,
sodium salt, 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 proce-
dure has a concentration of 1000 mg/l free
chlorine.
Further investigational concentrations may be
prepared from this stock solution by diluting
accordingly.
Stability:
When stored in a cool place (refrigerator), the
stock solution and the diluted investigational
solutions remain stable for one day.
Reagents required:
1.02426.0250 Dichloroisocyanuric acid,
sodium salt, GR for analysis
1.16754.9010 Water GR for analysis
Standard solution of total chlorine
Preparation of a standard solution:
Dissolve 4.00 g of chloramine T 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 total chlorine.
Further investigational concentrations may be
prepared from this stock solution by diluting
accordingly.
Stability:
When stored in a cool place (refrigerator), the
stock solution and the diluted investigational
solutions remain stable for one day.
Reagents required:
1.02426.0250 Chloramine T GR for analysis
1.16754.9010 Water GR for analysis
XXI
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