Fractional determination of nitric acid and phosphoric acid | Autotitr

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)KFM/(S10)
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)KFM/(S10) ※
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 %