HIRANUMA APPLICATION DATA

Automatic Titrator

Data No.

J11Feb. 10,
2021

Fractional determination ofnitric acid and phosphoric acid

Inorganic acids &Mixed acids
1. Abstract

The mixed solution of nitric acid and phosphoric acid works as strong acid, and also has the strongoxidizability and solvency. It is used as the surface treatment solution for metals, glass products, andsemiconductors.
This report introduces an example of the fractional and successive determination for nitric acid andphosphoric acid by neutralization titration with sodium hydroxide standard solution. When nitric acid andphosphoric acid are titrated by neutralization titration using a glass electrode for pH measurement, two
inflection points appear on the titration curve. The first inflection point appears as the total amount of nitricacid and phosphoric acid (reaction formula (1) and (2)). Sodium dihydrogen phosphate, which is the product ofreaction equation (2), subsequently reacts with sodium hydroxide and shows an inflection point in the second
stage (reaction equation (3)). Therefore, it is possible to obtain the phosphoric acid concentration from thesecond inflection point, and nitric acid concentration could be obtained with subtracting titration volume at thesecond inflection point from the first inflection point.
HNO3＋

NaOH

→

NaNO3＋H2O・・・（1）

H3PO4＋NaOH→

NaH2PO4＋H2O・・・（2）

NaH2PO4＋NaOH→

Na2HPO4＋H2O・・・（3）2. Configuration of instruments and reagents(1) Configuration of instruments
Main unit:

Automatic Titrator COM series

Electrodes:

Glass electrodeGE-101B (Connect to IE-1)

Reference electrodeRE-201Z (Connect to RE-1)(2) Reagent
Titrant:

1 mol/L Sodium hydroxide standard solution (For volumetric analysis)3. Measurement procedure(1) Take 1 mL of sample into a 100 mL beaker with a micropipette and accurately weigh it.
(2) Add 50 mL of DI water and a stirrer bar.
(3) Immerse electrodes and titrate with 1 mol/L sodium hydroxide standard solution until second inflection
point is detected.

4. Measurement conditions and results
Examples of titration conditions(1) Titration condition for total acidCndt No.
6Method
AutoBuret No.
1Amp No.
1
D. Unit
pHS-Timer
0 sec
C.P. mL0 mLT Timer
0 sec
D.P. mL0 mL
End Sens
500
Over mL
0 mL
Max.Vol.
40 mL

ConstantNo.
SizeBlank
Molarity
FactorKL
Unit
FormulaDigits

60 g0 mL
1 mol/L
1.005
630Mode No.
4Pre Int
0Del K
9Del Sens
0Int Time
3Int Sens
3Brt Speed
2Pulse
40sec
mVsec
mV

mL
D
3(2) Titration condition for phosphoric acid

Cndt No.
7MethodAuto
Buret No.
1Amp No.
1
D. UnitpH
S-Timer
0 sec
C.P. mL
0 mL
T Timer
0 sec
D.P. mL
0 mL
End Sens
500
Over mL
0.3 mL
Max.Vol.
20 mL

ConstantNo.
SizeBlank
Molarity
FactorKL

70 g0 mL
1 mol/L
1.005
980Mode No.
8Pre Int0Del K5Del Sens0Int Time5Int Sens
3Brt Speed
2Pulse40secmVsec
mV

Unit%
Formula(VB-B)*K*F*M/(S*10)
Digits3(3) Calculation for nitric acid

Cndt No.
Method8Calc

ConstantNo.
SizeBlank
Molarity
FactorKL

80 g0 mL
1 mol/L
1.005
63.01
0

Unit%
Formula(VA-VB)*K*F*M/(S*10)※
Digits3※ If the titrator is a model manufactured before 2009 (COM-1600, etc.), set (x, y) instead of the coefficient(VA, VB) in the formula. The calculation function is the same.

Measurement results
Number ofmeasurement

Samplesize (g)1231.45081.45111.4609Total acid

Phosphoric acid

Nitric acid

Titrant
volume (mL)

Titrant
volume (mL)

Conc.
(%)

Conc.
(%)

10.501
10.55410.562

8.243
8.294
8.298

55.95956.29455.94356.07 %
0.20 %
0.4 %

9.90189.78369.78909.82 %
0.07 %
0.7 %

Avg.
SDRSD

Example of titration curve

5. NoteIf the sample contains metal ions, the formation of these hydroxide salts may consume the titrant.

Keywords：Nitric acid, Phosphoric acid, Fractional titration, Potentiometric titration, Neutralization titration*Some measurement would not be possible depending on optional configuration of system.