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
To Next Page
Loading...
