Fractional determination of acetic acid and ammonium acetate | Autotitrator COM-A19 - JM Science
HIRANUMA APPLICATION DATA Automatic Titrator Data No. K7 Feb. 10,2021
Organic acid Fractional determination of acetic acid and ammonium acetate

1. Abstract

The mixed solution of acetic acid and ammonium acetate is used as washing solution on the production process of semiconductor. There are some determination methods for the fractional determination of a weak acid and a salt of a weak acid. The formaldehyde addition method which is the most typical determination method is introduced in this report.

First, the neutralization titration is performed for acetic acid with sodium hydroxide (formula (1)). After that, acetic acid and hexamethylenetetramine equivalent to ammonium acetate are generated by adding formaldehyde (formula (2)). Finally, the generated acetic acid is continuously titrated with sodium hydroxide to determine the ammonium acetate.

CH₃COOH + NaOH → CH₃COONa + H₂O  ・・・(1)
4CH₃COONH₄ + 6HCHO → 4CH₃COOH + C₆H₁₂N₄ + 6H₂O  ・・・(2)
Hexamethylenetetramine  

2. Configuration of instruments and Reagents

(1) Configuration
  Main unit : Automatic Titrator COM series
  Option : One buret
  Electrode : Glass electrode GE-101B
Reference electrode RE-201Z
*Instead of above electrodes, the following combination electrodes are usable.
・GR-501BZ (Fixed sleeve type)
・GR-511BZ (Flexible sleeve type)
(2) Reagents    
  Titrant : 0.1 mol/L Sodium hydroxide standard solution
  Additive : 35 % Formaldehyde

3. Measurement procedure

(1) Take 1 mL of sample into a 100 mL beaker with a volumetric pipette.
(2) Add about 50 mL of DI water.
(3) Immerse the electrodes to start titration. The titration with 0.1 mol/L sodium hydroxide for acetic acid, dispensing formaldehyde by an optional buret, and the titration with 0.1 mol/L sodium hydroxide for ammonium acetate are sequentially performed.

4. Measurement conditions and results

Examples of titration conditions

(1) Titration for acetic acid

Cndt No 1
Method Auto
Buret No. 1
Amp No. 1
D. Unit pH
S-Timer 5 sec
C.P. mL 0 mL
T Timer 0 sec
D.P. mL 0 mL
End Sens 300
Over mL 0 mL
Max Vol. 20 mL
Constant No. 1
Size 1 mL
Blank 0 mL
Molarity 0.1 mol/L
Factor 1.006
K 60.05
L 0
Unit %
Formula
(D-B)*K*F*M/(S*10)
Decimal Places 3
Auto input Param.
None
Mode No. 5
Pre Int 0 sec
Del K 5
Del Sens 0 mV
Int Time 3 sec
Int Sens 3 mV
Brt Speed 2
Pulse 40

 

(2) Dispense formaldehyde.

Cndt No 2  
Method Disp  
Buret No. 2  
S-Timer 0 sec
Disp Vol. 5 mL

 

(3) Titration for ammonium acetate

Cndt No 3
Method Auto
Buret No. 1
Amp No. 1
D. Unit pH
S-Timer 15 sec
C.P. mL 0 mL
T Timer 0 sec
D.P. mL 0.3 mL
End Sens 500
Over mL 0.3 mL
Max Vol. 20 mL
Constant No. 3
Size 1 mL
Blank 0 mL
Molarity 0.1 mol/L
Factor 1.006
K 77.08
L 0
Unit %
Formula
(D-B)*K*F*M/(S*10)
Decimal Places 3
Auto input Param.
None
Mode No. 5
Pre Int 0 sec
Del K 5
Del Sens 0 mV
Int Time 3 sec
Int Sens 3 mV
Brt Speed 2
Pulse 40

 

Measurement results

Measurement results of acetic acid

Number of
measurement
Size
(mL)
Titrant
volume(mL)
Acetic acid
Concentration(%)
1 1 4.928 2.977
2 1 4.920 2.972
3 1 4.916 2.970
Statistic
calculation
Average 2.973 %
Standard deviation 0.0036 %
Coefficient of variation 0.121 %

 

Measurement results of ammonium acetate

Number of
measurement
Size
(mL)
Titrant
volume(mL)
Ammonium acetate
Concentration(%)
1 1 8.976 6.960
2 1 8.965 6.952
3 1 8.957 6.945
Statistic
calculation
Average 6.952 %
Standard deviation 0.0075 %
Coefficient of variation 0.108 %

 

Examples of titration curves

5. Note

Another method for successive titration

There is a method without adding formaldehyde for fractional determination other than the method described in this report. The sample is titrated with sodium hydroxide standard solution in this method; the first inflection point indicates the end point for acetic acid, and the second inflection point is obtained as the end point for ammonium acetate. The advantage of this method is that the addition of formaldehyde is not required. On the other hand, the second end point of ammonium acetate sometimes gets unclear inflection point depending on the concentration of the ammonium acetate. The right figure shows an example of titration curve on this method.

Keywords: Acetic acid, Ammonium acetate, Sodium hydroxide, Formaldehyde, Neutralization titration

*Some measurement would not be possible depending on optional configuration of system.

Hiranuma aquacounter autotitrator com-a19Organic acid

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