Hanna Instruments HI931, User Manual, Page: 175 / 218

5
0.1M SODIUM THIOSULF
ATE TITRANT CONCENTRA
TION
0.1M SODIUM THIOSULFATE TITRANT CONCENTRATION
METHOD ID: HI0003EN
DESCRIPTION
Method for the standardization (titer determination) of 0.1M
Sodium Thiosulfate (Na
2
S
2
O
3
) titrant solution against Potassium
Iodate (KIO
3
). The results are expressed in M (mol/L) .
REFERENCE
Standard Methods for the Examination of Water and Wastewater
19
th
Edition, Method 4500-Cl B
ELECTRODE
• HI3131B Combination ORP Electrode
REAGENTS
• HI70439 0.1M Sodium Thiosulfate (1 L)
• HI70407 Potassium Iodate (20 g)
• HI70425 16% Sulfuric Acid (500 mL)
• HI70468 Potassium Iodide (35 g)
• HI70436 Deionized Water (1 gal)
ACCESSORIES
• HI70300L Storage Solution (500 mL)
• HI7071 Electrode Fill Solution (30 mL x 4)
• HI740036P 100 mL Plastic Beakers (10 pcs)
• Analytical Balance 0.0001 g
• 100 mL Class A Volumetric Flask
• 10 mL Class A Volumetric Pipette
DEVICE PREPARATION
• Connect the ORP electrode to the titrator.
• Install a 25 mL burette filled with 0.1M sodium thiosulfate
(HI70439) on pump one and verify that no air bubbles are
present in the burette or tubing. If necessary prime the burette
until all the air has been removed completely.
• Press from the main screen. Use the arrow keys
to highlight HI0003EN 0.1M Sodium Thiosulfate and press
.
ELECTRODE PREPARATION
• Prepare the ORP electrode according to the procedure in the
manual.
SAMPLE PREPARATION
• Crush approximately 2 grams of potassium iodate (HI70407)
and dry it for 2 hours at 120°C. Cool to room temperature in a
desiccator.
• Carefully weigh approximately 0.35 grams of dried potassium
iodate.
• Record the exact weight of the sample once the balance has
stabilized with an accuracy of 0.0001 grams.
• Carefully transfer the salt to a 100 mL Class A volumetric flask.
Add approximately 80 mL of deionized water, and mix to
dissolve. Once the salt is completely dissolved bring the flask to
volume with deionized water, mix well.
• Use a Class A volumetric pipette to transfer exactly 10.00 mL of
the solution to a clean 100 mL plastic beaker.
• Add deionized water to the 50 mL mark on the beaker.
• Add 5.00 mL of 16% sulfuric acid (HI70425) and 1.5 grams of
potassium iodide (HI70468) to the beaker.
ANALYSIS
• Place the beaker under the stirrer assembly and lower it to
immerse the ORP electrode and stirrer. Ensure that the reference
junction of the ORP electrode is 5 to 6 mm below the surface. If
necessary add extra deionized water.
Note:
The dispensing tip should be slightly submerged in the
sample.
• Press . You will be prompted to enter the weight of the
analyte (weight of potassium iodate). Use the numeric keypad
to enter the exact weight and press
to start the analysis.
• At the end of the titration, after detection of the equivalence
point, “Titration Completed” will appear with the result. The
result is expressed in
M (mol/L) of sodium thiosulfate .
• Remove the ORP electrode and stirrer from the sample and rinse
them thoroughly with deionized water.
• Record the result.
Note:
For improved accuracy, repeat this procedure a minimum
of three times and calculate the average value.
For methods utilizing 0.1M sodium thiosulfate titrant solution,
follow the steps below to enter the titer/standardized value.
• Select the method utilizing 0.1M sodium thiosulfate.
• Press
from the main screen.
• Using the arrow keys, highlight
Titrant Conc.
and press
.
• Use the numeric keypad to enter the standardized (titer) value
of the titrant then press .
• Press to exit the View/Modify Method screen. Use
the arrow keys to highlight Save Method and press .