Hanna Instruments HI 902 Color, Quick Start Manual

Page: 203 / 248

Method ID: HI0010EN
0.1M Ferrous Ammonium Sulfate Titrant Concentration
(Ferrous Ammonium Sulfate
– FAS)
Titrator Application Methods: General Methods - r. 2.3
Description:
Method for the standardization (titer determination)
of
0.1M Ferrous Ammonium Sulfate
[Fe(NH
4
)
2
(SO
4
)
2
*6H
2
O] titrant solution, against
Potassium Dichromate [K
2
Cr
2
O
7
]. The results are
expressed in M (mol/L) .
Reference:
Standard Methods for the Examination of Water and
Wastewater 21
st
edition, Method 5220B.
Electrode :

HI 3131B Combination ORP Electrode
Reagents :

HI 70444 25% Sulfuric Acid (500 mL)

HI 70436 Distilled Water (1 gal)

Ferrous Ammonium Sulfate Hexahydrate (ACS
grade or better)

Potassium Dichromate (ACS grade or better)
Accessories :

HI 70300L Storage Solution (500 mL)

HI 7071 Electrode Fill Solution (4*30 mL)

HI 740036P100-mL Plastic Beakers (10 pcs.)

Analytical Balance with a minimum resolution of
0.0001g is recommended

100-mL Class-A Volumetric Flasks

500-mL Class-A Volumetric Flasks

10-mL Class-A Volumetric pipette
Procedure :

Connect the ORP electrode to the titrator.

Press “
Select Method
” from the main screen. Use
the arrow keys to
highlight „HI0010EN 0.1M FAS
Titr. Conc.‟ and press “
Select
”.

Install a 25-mL burette with 0.1M FAS solution 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.
NOTE : To prepare a 0.1M FAS titrant solution:
Add 19.607 g FAS to a 500-mL class-A volumetric
flask. Add about 300 mL of distilled water, then
add 40 mL of 25% sulfuric acid (HI 70444) to the
flask. Invert the solution to mix. Allow the flask to
return to room temperature before bringing to
volume with distilled water.

Dry approximately 2 grams of potassium
dichromate for 2 hours at 150°C. Cool to room
temperature in a desiccator before using.

Weigh 0.49 g of dried potassium dichromate 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 clean 100-mL plastic beaker and 25 mL of 25%
sulfuric acid solution (HI 70444). Use distilled
water to bring the total volume to about 50 mL.

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 K
2
Cr
2
O
7
). 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, the message „titration
completed‟ will appear with the titrant
concentration. The result is expressed in M
(mol/L) of ferrous ammonium sulfate .

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 average
value.
For methods utilizing 0.1M Ferrous Ammonium
Sulfate titrant solution, follow the steps below to
enter the titer/standardized value.

Select the method utilizing 0.1M FAS.

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.
NOTE: Standardize the Ferrous Ammonium Sulfate
titrant solution daily.
Method Parameters :
Name: 0.1M FAS 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: 0.500 mL
delta E: 4.500 mV
End Point Mode: mV 1EQ point, 1st Der.
Recognition Options:
Threshold: 35 mV/mL
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