Hanna Instruments HI 902 Color, Quick Start Manual

Page: 201 / 248

Method ID: HI0003EN
0.1M Sodium Thiosulfate Titrant Concentration
Titrator Application Methods: General Methods - r. 2.3
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:
Adaptation of AOAC Official Methods of Analysis,
Official Method 942.27
Electrode :

HI 3131B Combination ORP Electrode
Reagents :

HI 70439 0.1M Sodium thiosulfate solution (1 L)

HI 70407 Potassium Iodate (20 g)

HI 70425 16% Sulfuric Acid (500 mL)

HI 70468 Potassium Iodide (35 g)

HI 70436 Distilled Water (1 gal)
Accessories :

HI 70300L Storage Solution (500 mL)

HI 7071 Electrode Fill Solution (4*30 mL)

Analytical Balance with a minimum resolution of
0.0001g is recommended

150-mL Glass Beakers

100-mL Class-A Volumetric Flask

10-mL Class-A Volumetric Pipette
Procedure :

Connect the ORP probe to the titrator.

Press “
Select Method
” from the main screen. Use
the arrow keys to highlight „HI0003EN 0.1M
Na2S2O3 Titr. Conc.‟ and press “
Select
”.

Install a 25-mL burette with 0.1M sodium
thiosulfate solution (HI 70439) on pump-one and
verify that no air bubbles are present in the burette
or tubing. If necessary prime until all air has been
removed completely.

Crush approximately 2 grams of potassium iodate
(HI 70407) and dry it for 2 hours at 120°C. Cool to
room temperature in a desiccator.

Weigh 0.35 g of dried potassium iodate with an
accuracy of 0.0001 g. Transfer the salt to a 100-
mL volumetric flask. Add approximately 80 mL of
distilled water and mix. Dissolve completely before
bringing to volume.

Use a class-A volumetric pipette to transfer
exactly 10.00 mL of prepared standard solution to
a 150-mL glass beaker and add distilled water to
the 100-mL mark on the beaker.

To the beaker add 5 mL of 16% sulfuric acid (HI
70425) and 1.5 g of potassium iodide (HI 70468).

Place the beaker under the stirrer assembly and
immerse the ORP electrode and stirrer. Ensure
that the reference junction of the ORP electrode is
5-6 mm below the surface. If necessary add extra
distilled water.

Press “
Start
”. You will be prompted to enter the
analyte size (weight of KIO
3
). Use the numeric
keypad to enter the exact weight and press
“
Enter
” to start the analysis.

At the end of the titration, after detection of the
equivalence point, „titration completed‟ will appear
with the titrant concentration. The result is
expressed in
M (mol/L) of sodium thiosulfate .

Remove the electrode and stirrer from the sample
and rinse them thoroughly with distilled water.

Record the result (titer concentration).
NOTE: For optimal accuracy repeat this procedure a
minimum of three times and calculate the mean
value.
For methods utilizing 0.1N Na
2
S
2
O
3
titrant
solution, follow the steps below to enter the
titer/standardized value.

Select the method utilizing 0.1N Na
2
S
2
O
3
.

Select „Method Options‟ from the main screen.

Using the arrow keys, highlight „Titrant Conc.‟ and
press “Select”.

Use the numeric keypad to enter the standardized
(titer) value of the titrant then press „Accept‟.

Press „Escape‟ to exit the Method Options screen
and select „Save Method‟ option.
Method Parameters :
Name: 0.1M Na2S2O3 Titr. Conc.
Method Revision: 2.3
Titration Type: Standard Titration
Analog Board: Analog 1
Stirrer Configuration: Stirrer 1
Pump Configuration:
Titrant Pump: Pump 1
Dosing Type: Dynamic
min Vol: 0.030 mL
max Vol: 0.600 mL
delta E: 6.500 mV
End Point Mode: mV 1EQ point, 1st Der.
Recognition Options:
Threshold: 50 mV/mL
Range: No
Filtered Derivatives: No
Pre-Titration Volume: 5.000 mL
Pre-Titration Stir Time: 0 sec
Measurement Mode: Signal Stability
delta E: 0.3 mV
delta t: 2.0 sec
t-min wait: 2 sec
t-max wait: 20 sec
Electrode Type: ORP
Blank Option: No Blank
Calculations: Stdz. Titrant by Weight
Dilution Option: Enabled
Final Dilution Volume: 100.000 mL
Aliquot Volume: 10.000 mL
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