HIRANUMA APPLICATION DATASODA PULP
INDUSTRY

Automatic Titrator

Data No.

H1Oct. 7,2022

Purity determination of sodium hydroxide

1. Abstract
Sodium hydroxide is one of the most elemental reagent in chemical industrial reagents. Its production
amount is large and it is used in a broad range of fields. Sodium hydroxide absorbs carbonate gas and water inatmosphere because of its properties, the purity of sodium hydroxide is gradually reduced. Japanese Industrial
Standard (JIS) K8576 defines determination method for purity of sodium hydroxide (titration with indicator).
Representative impure substance in sodium hydroxide includes sodium carbonate.
This report introduces an example for the quantitative determination of sodium hydroxide purity andsodium carbonate by successive and fractional potentiometric titration.
First, sodium carbonate is precipitated as barium carbonate by adding barium chloride before the titration(formula (1)). Secondly, most sodium hydroxide is titrated with highly concentrated hydrochloric acid standard
solution. After that, residual sodium hydroxide is titrated with low-concentrated hydrochloric acid standard
solution. It enhances the accuracy of quantitative determination for sodium hydroxide. Barium carbonate
generated on pretreatment is continuously titrated with low-concentrated hydrochloric acid standard solution.
The titrated volume for carbonate is doubled compared with the procedure without adding barium chloride, so it
is especially available for the small amount determination of carbonate.

Na2CO3 + BaCl2
NaOH＋HCl
BaCO3 ＋ 2 HCl→

BaCO3↓ ＋ 2NaCl (Pretreatment)
……(1)
→
NaCl＋
H2O
…………………(2)→BaCl2＋ CO2 ＋ H2O (Titration)……(3)The reaction between sodium hydroxide and hydrochloric acid is described in formula (2). Formula (3)shows the reaction between barium carbonate and hydrochloric acid. The pHs reach 9 and 4 on the reaction (2)and (3) at each end point.

2. Configuration of instruments and reagents(1) Configuration
Main unit ：Option：Electrode ：：Hiranuma Automatic Titrator COM series
One buretGlass electrodeGE-101B

Reference 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：

1.0 mol/L Hydrochloric acid standard solution
0.1 mol/L Hydrochloric acid standard solution

Additive ：10 % Barium chloride solution

3. Measurement procedure 。
(1) Take about 1.5 g of sample into 200 mL beaker and accurately weigh it.
(2) Add 50 mL of DI water which does not contain carbon dioxide, and dissolve the sample.
(3) Add 10mL of 10 % barium chloride solution. Flow nitrogen gas to the headspace on sample solution with
300 mL/min flow rate.
(4) Immerse the electrodes with keeping nitrogen gas flowing, and start titration. 1.0 mol/L hydrochloric acidstandard solution is dispensed first (35 mL here)*, and secondly 0.1 mol/L hydrochloric acid standard
solution is titrated. *Addition amount of 1.0 mol/L hydrochloric acid is equivalent to 90 % of sodiumhydroxide in sample solution.

4. Measurement conditions and results
Examples of titration conditions(1) Dispense 1.0 mol/L hydrochloric acid
Cndt No.
MethodBuret No.
S-Timer
Disp Vol.

1
Disp
1
5 sec
35 mL

(2) Titration of sodium hydroxide
Cndt No.
MethodBuret No.
Amp No.
D. UnitS-Timer
C.P. mLT Timer
D.P. mLEnd Sens
Over mL
Max. volume2Auto21pH50001000040sec
mLsec
mL
mL
mL

Constant No.
2Size
1.5002
Blank
35
Molarity
0.10
Factor
1.004
K40.00
L1.001
Unit%Formula(D*F*M+B*L)*K/(S*10)
Digits3Auto input parameter

gmLmol/L

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

505033240sec
mV
sec
mV

None

*Enter the dispensing volume and factor of 1.0 mol/L hydrochloric acid standard solution in B (Blank) and L (coefficient 2), respectively.

(3) Titration of sodium carbonate (sodium carbonate)
Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mLT Timer
D.P. mLEnd Sens
Over mL
Max. volume

3
Auto2
1
pH0000500
0.2
2sec
mL
sec
mL
mL
mL

Constant No.
3
Size1.5002Blank
0
Molarity
0.10
Factor
1.004
K53.00L
0Unit%
Formula(D-B)*K*F*M/(S*10)
Digits3
Auto input parameter

gmL
mol/L

None

Mode No.
Pre Int
Del K
Del Sens
Int Time
Int Sens
Brt Speed
Pulse

805053240sec
mVsecmVMeasurement results
Measurement results of sodium hydroxide
Number ofSize

Titrant

Concentration

Measurement(g)

Volume (mL)(%)

11.5396

22.99897.02321.5002

13.59097.0523

1.511015.97096.991

Statistic
calculation

Average97.02 %

Standard deviation

0.031 %

Coefficient of variation

0.03 %

Measurement results of sodium carbonate

Example of titration curve

Number ofSize

Titrant

Concentration

Measurement(g)

Volume (mL)(%)

1

1.5396

1.236

0.429

2

1.5002

1.152

0.409

3

1.5110

1.085

0.382

Statistic
calculationAverage

0.407 %

Standard deviation

0.024 %

Coefficient of variation

5.80 %

5. NoteAtmosphere environment
Atmosphere contains about 0.03 % carbon dioxide. When carbon dioxide is absorbed into sample solution
during titration for sodium hydroxide, the titrant volume consumed for sodium hydroxide is decreased, while it isincreased on the titration for sodium carbonate. Flowing nitrogen gas to the headspace on sample solution serves
as an effective measure against this problem. Using air passed through soda lime absorption column instead ofnitrogen gas also has a positive effect.
Keywords：Sodium hydroxide, Sodium carbonate, Neutralization titration, Barium carbonate, JIS K 8576