Fractional determination of nitric acid and phosphoric acid | Autotitrator COM-A19 - JM Science
HIRANUMA APPLICATION DATA Automatic Titrator Data No. J11 Feb.10,2021
Inorganic acids & Mixed acids Fractional determination of nitric acid and phosphoric acid

1. Abstract

The mixed solution of nitric acid and phosphoric acid works as strong acid, and also has the strong oxidizability and solvency. It is used as the surface treatment solution for metals, glass products, and semiconductors.

This report introduces an example of the fractional and successive determination for nitric acid and phosphoric acid by neutralization titration with sodium hydroxide standard solution. When nitric acid and phosphoric 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 nitric acid and phosphoric acid (reaction formula (1) and (2)). Sodium dihydrogen phosphate, which is the product of reaction 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 the second inflection point, and nitric acid concentration could be obtained with subtracting titration volume at the second 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 electrode GE-101B (Connect to IE-1)
Reference electrode RE-201Z (Connect to RE-1)
(2) Reagents    
  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 acid

Cndt No 6
Method Auto
Buret No. 1
Amp No. 1
D. Unit pH
S-Timer 0 sec
C.P. mL 0 mL
T Timer 0 sec
D.P. mL 0 mL
End Sens 500
Over mL 0 mL
Max Vol. 40 mL
Constant No. 6
Size 0 g
Blank 0 mL
Molarity 1 mol/L
Factor 1.005
K 63
L 0
Unit mL
Formula D
Digits 3
Mode No. 4
Pre Int 0 sec
Del K 9
Del Sens 0 mV
Int Time 3 sec
Int Sens 3 mV
Brt Speed 2
Pulse 40

 

(2) Titration condition for phosphoric acid

Cndt No 7
Method Auto
Buret No. 1
Amp No. 1
D. Unit pH
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
Constant No. 7
Size 0 g
Blank 0 mL
Molarity 1 mol/L
Factor 1.005
K 98
L 0
Unit %
Formula (VB-B)*K*F*M/(S*10)
Digits 3
Mode No. 8
Pre Int 0 sec
Del K 5
Del Sens 0 mV
Int Time 5 sec
Int Sens 3 mV
Brt Speed 2
Pulse 40

 

(3) Calculation for nitric acid

Cndt No 8
Method Calc
Constant No. 8
Size 0 g
Blank 0 mL
Molarity 1 mol/L
Factor 1.005
K 63.01
L 0
Unit %
Formula (VA-VB)*K*F*M/(S*10) ※
Digits 3
※ 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 of
measurement
Sample
size(g)
Total acid
Titrant
Volume(mL)
Phosphoric acid
Titrant
volume(mL)
 
Conc.
(%)
Nitric acid
Conc.
(%)
1 1.4508 10.501 8.243 55.959 9.9018
2 1.4511 10.554 8.294 56.294 9.7836
3 1.4609 10.562 8.298 55.943 9.7890
      Avg. 56.07 % 9.82 %
      SD 0.20 % 0.07 %
      RSD 0.4 % 0.7 %

Examples of titration curves

5.Note

If 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.

Hiranuma aquacounter autotitrator com-a19Inorganic acids & mixed acids

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