Fractional determination of nitric acid and acetic acid | Autotitrator

HIRANUMA APPLICATION DATA

Automatic Titrator

Data No.

Apr. 5,2019

Inorganic acids & Mixed acids

Fractional determination of nitric acid and acetic acid

1. Abstract

The mixed solution of nitric acid (inorganic acid) and acetic acid (organic 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 acetic acid by neutralization titration with sodium hydroxide standard solution.

HNO₃ + NaOH → NaNO₃ + H₂O	・・・(1)
CH₃COOH + NaOH → CH₃COONa + H₂O	・・・(2)

2. Configuration of instruments and Reagents

(1)	Configuration of instruments
	Main unit	:	Hiranuma Automatic Titrator COM series
	Electrodes	:	Glass electrode GE-101B Reference electrode RE-201Z *Instead of the above electrodes, the following electrodes are usable. ・Glass reference combination electrode GR-501BZ…Fixed sleeve type ・Glass reference combination electrode GR-511BZ…Moveable sleeve type
(2)	Reagents
	Titrant	:	1 mol/L Sodium hydroxide standard solution

3. Measurement procedure

(1)	Dispense 1 mL of sample into a 100 mL beaker with a volumetric pipette.
(2)	Add 40 mL of CO₂-free DI water.
(3)	Immerse electrodes and start titration with 1 mol/L sodium hydroxide standard solution.

4. Measurement conditions and results

Examples of titration conditions

(1) Titration condition for nitric acid

Cndt No	1
Method	Auto
Buret No.	1
Amp No.	1
D. Unit	pH
S-Timer	10	sec
C.P. mL	0	mL
T Timer	0	sec
D.P. mL	0	mL
End Sens	150
Over mL	0	mL
Max Vol.	20	mL

Constant No.	1
Size	1	mL
Blank	0	mL
Molarity	1	mol/L
Factor	1.005
K	63.01
L	0
Unit	g/L
Formula	(D-M)KF*M/S

Decimal Places	3
Auto In Pram.		None

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 acetic acid

Cndt No	2
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	1000
Over mL	0.2	mL
Max Vol.	20	mL

Constant No.	2
Size	1	mL
Blank	0	mL
Molarity	1	mol/L
Factor	1.005
K	60.05
L	0
Unit	g/L
Formula	(D-M)KF*M/S

Decimal Places	3
Auto In Pram.		None

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

*Connect the condition (1) and (2) for successive titration.

Measurement results

Number of measurement	Size (mL)	Titrant volume at 1st endpoint (mL)	Nitric acid (g/L)	Titrant volume at 2nd endpoint (mL)	Acetic acid (g/L)
1	1	4.708	289.134	8.314	501.752
2	1	4.709	298.198	8.311	501.571
3	1	4.710	298.261	8.318	501.993
Statistic calculation		Avg.	295.2 g/L	Avg.	501.8 g/L
		SD	5.25 g/L	SD	0.21 g/L
		RSD	1.78 %	RSD	0.04 %

Examples of titration curves

5. Note

・Control of titrant
The concentrated sodium hydroxide standard solution is used as titrant in this report. The carbon dioxide gas absorber (soda lime) on reagent bottle has to be regularly exchanged because sodium hydroxide readily absorbs carbon dioxide gas in the air (formula (3)). The titrant contains sodium carbonate if it absorbed carbon dioxide gas. When using this titrant, the titration curve would show the inflection points at pH around 4 and 9 (formula (4) and (5)).

2NaOH + CO₂ → Na₂CO₃ + H₂O	・・・(3)
Na₂CO₃ + HNO₃ → NaHCO₃ + NaNO₃	・・・(4)
NaHCO₃ + HNO₃ → NaNO₃ + CO₂ + H₂O	・・・(5)