Hanna Instruments HI 902 Color, Quick Start Manual

Page: 221 / 248

Method ID: HI1014EN
Concentration of Phosphoric Acid
0.00000
–1.0000
-2
mol/L
Titrator Application Methods: General Methods - r. 2.3
Description:
Method for the determination of phosphoric acid
(H
3
PO
4
), by titration of a sample to the point of
inflection.
The first inflection point corresponds to the H
3
PO
4
content, and the difference between the first and
second corresponds to H
2
PO
4
¯. The results are
expressed in M (mol/L) .
If only phosphoric acid and no other acids or bases
are present in the sample, then [H
3
PO
4
] = [H
2
PO
4
¯].
If [H
3
PO
4
] > [H
2
PO
4
¯], this means that other strong
acids are also present (e.g., hydrochloric or sulfuric
acid). If [H
3
PO
4
] < [H
2
PO
4
¯] this means that other
weak acids or bases are present (e.g., citric acid /
citrate, or ascorbic acid / ascorbate).
Electrode :

HI 1131B Combination pH Electrode

HI 7662-T Temperature Probe
Reagents :

HI 70456 0.1N Sodium Hydroxide solution (1 L)

HI 70436 Distilled Water (1 gal)
Accessories :

HI 70300L Storage Solution (500 mL)

HI 7071 Electrode Fill Solution (4*30 mL)

HI 7004L pH 4.01 Buffer Solution (500 mL)

HI 7007L pH 7.01 Buffer Solution (500 mL)

HI 7010L pH 10.01 Buffer Solution (500 mL)

100-mL Class-A Volumetric Pipette

150-mL Glass Beakers
NOTE : For this method it is not necessary to
calibrate the pH electrode first.
Procedure :

Connect the pH electrode and temperature probe
to the titrator.

Press “
Select Method
” from the main screen. Use
the arr
ow keys to highlight „HI1014EN
Concentration of H3PO4‟ and press “
Select
”.

Install a 25-mL burette with 0.1N sodium
hydroxide solution (HI 70456) 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.

For sparkling samples, remove the CO
2
by
passing nitrogen through it, using an ultrasonic
bath, or by stirring and applying vacuum.

Use a class-A volumetric pipette to transfer
exactly 100.00 mL of sample to a clean 150-mL
glass beaker.

Place the beaker under the stirrer assembly and
immerse the pH electrode, temperature probe and
stirrer. Ensure that the reference junction of the
pH probe is 5-6 mm below the surface.

Press “
Start
”. The titrator will start the analysis.

At the end of the titration, after detection of the
second equivalence point, the message „titration
completed‟ will appear with the phosphoric acid
concentration.
The first equivalence point
corresponds to the H
3
PO
4
concentration and the
second equivalence point corresponds to the
H
2
PO
4
¯ concentration.

Remove the electrodes and stirrer from the
sample and rinse them thoroughly with distilled
water.

Record the result.
Method Parameters :
Name: Concentration of H3PO4
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: 8.000 mV
End Point Mode: pH 2EQ points, 1st Der.
Recognition Options:
Threshold: 50 mV/mL
Range: No
Filtered Derivatives: No
Pre-Titration Volume: 0.000 mL
Pre-Titration Stir Time: 10 sec
Measurement Mode: Signal Stability
delta E: 0.8 mV
delta t: 1.5 sec
t-min wait: 2 sec
t-max wait: 20 sec
Electrode Type: pH
Blank Option: No Blank
Calculations: Sample Calc. by Volume
Dilution Option: Disabled
Titrant Name: 0.1N NaOH
Titrant Conc.: 0.1000 N (eq/L)
Analyte Size: 100.00 mL
Analyte Entry: Fixed
Maximum Titrant Volume: 20.000 mL
Stirring Speed: 1400 rpm
Potential Range: -2000.0 to 2000.0 mV
Volume/Flow Rate: 25 mL/50 mL/min
Signal Averaging: 1 Reading
Significant Figures: XXXXX
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