HIRANUMA APPLICATION DATA

Automatic Titrator

Data No.

K7Feb. 10,
2021

Fractional determination of acetic acid andammonium acetate

Organic acid
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 acidand a salt of a weak acid. The formaldehyde addition method which is the most typical determination method isintroduced 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 todetermine 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 ：Option：Electrode ：：Automatic Titrator COM series
One buretGlass electrodeGE-101BReference electrodeRE-201Z*Instead of above electrodes, the following combination electrodes are usable.
・GR-501BZ (Fixed sleeve type)・GR-511BZ (Flexible sleeve type)(2) Reagents
Titrant：

Additive ：0.1 mol/L Sodium hydroxide standard solution
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 forammonium acetate are sequentially performed.

4. Measurement conditions and results
Examples of titration conditions(1) Titration for acetic acidCndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mLT Timer
D.P. mLEnd Sens
Over mLMax Vol.

1Auto
1
1pH
5000300
020sec
mL
sec
mL
mL
mL

Constant No.
1Size
1Blank0
Molarity
0.1
Factor
1.006
K60.05
LUnit%
Formula(D-B)*K*F*M/(S*10)
Decimal places3Auto input parameter

mLmLmol/L

Mode No.
Pre Int
Del K
Del Sens
Int Time
Int Sens
Brt SpeedPulse

505033240Mode No.
Pre Int
Del K
Del Sens
Int Time
Int Sens
Brt SpeedPulse

505033240sec
mVsec
mV

None

(2) Dispense formaldehyde.
Cndt No.
MethodBuret No.
S-Timer
Disp Vol.

2
Disp
20 sec5 mL(3) Titration for ammonium acetate
Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-TimerC.P. mL
T Timer
D.P. mLEnd Sens
Over mLMax Vol.

3Auto11pH
15000.3
500
0.3
20sec
mL
sec
mL
mL
mL

Constant No.
3
Size
1Blank0
Molarity
0.1
Factor
1.006
K77.08
L0Unit%Formula(D-B)*K*F*M/(S*10)
Decimal places
3Auto input parameter

mL
mL
mol/L

NonesecmV
secmVMeasurement results
Measurement results of acetic acid
Number ofSize

Titrant

Acetic acid

Measurement(mL)

Volume (mL)Concentration (%)

11

4.928

2.977

21

4.920

2.972

31

4.916

2.970

Statistic
calculation

Average

2.973 %

Standard deviation

0.0036 %Coefficient of variation

0.121 %

Measurement results of ammonium acetate

Example of titration curve

Number ofSize

Titrant

Ammonium acetate

Measurement(mL)

Volume (mL)Concentration (%)

1

1

8.976

6.960

2

1

8.965

6.952

3

1

8.957

6.945

Statisticcalculation

Average

6.952 %

Standard deviation

0.0075 %Coefficient of variation

0.108 %

5. NoteAnother 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 thismethod; the first inflection point indicates the end point for acetic
acid, and the second inflection point is obtained as the end point forammonium acetate. The advantage of this method is that the additionof 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 rightfigure 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.