HIRANUMA APPLICATION DATASODA PULP
INDUSTRY

Data No.

Automatic Titrator

H2Apr. 5,
2019

Fractional determination for mixture ofsodium hydroxide and sodium carbonate

1. AbstractSodium hydroxide and sodium carbonate have important roles as alkali component chemicals, which areused in a broad range of industries. The concentration of both components have to be determined because theseare sometimes used with mixed.
This report introduces an example that the mixture solution of sodium hydroxide and sodium carbonate are
fractionally determined with potentiometric titration. The titration of sodium hydroxide and sodium carbonate
with hydrochloric acid proceeds as the following reaction formula:→→NaOH ＋ HCl
Na2CO3 ＋ HCl

NaCl＋NaHCO3 ＋H2ONaCl･･･(1)･･･(2)The pH reaches around 9 at the end point on the reaction formula (1) and (2). Sodium carbonate generates
sodium hydrogen carbonate (NaHCO3) on the reaction (2), then continuously generated sodium hydrogencarbonate is titrated with hydrochloric acid. It reaches the end point at pH around 4. The reaction between sodiumhydrogen carbonate and hydrochloric acid is described in the formula (3).

NaHCO3 ＋HCl→

NaCl＋

CO2＋H2O･･･(3)The relation of titration curve and formula (1)(2)(3) is illustrated in the following figure.

pHNaOH
Na2CO3Titration volume (mL)

NaHCO3*Some measurement would not be possible depending on optional configuration of system.

2. Configuration of instruments and reagents(1) Configuration of instruments
Main unit: Hiranuma Automatic Titrator COM series

Electrodes: Glass electrodeGE-101B: Reference electrodeRE-201Z*

Instead of above electrode, the following glass reference electrodes are usable.

・GR-501BZ (Glass reference combination electrode)…Fixed sleeve type・GR-511BZ (Glass reference combination electrode)…Moveable sleeve type(2) Reagent
Titrant: 0.1 mol/L Hydrochloric acid standard solution

3. Measurement procedure(1) Dispense 20 mL of sample into a 100 mL beaker with volumetric pipette.
(2) Add 30 mL of DI water.
(3) Immerse the electrodes and titrate with 0.1 mol/L hydrochloric acid standard solution.

4. Measurement conditions and results
Examples of titration conditions(1) Measurement condition of sodium hydroxide and sodium carbonate
Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mLT Timer
D.P. mLEnd Sens
Over mL
Max.Vol.

1Auto
11pH
50001000
020sec
mL
sec
mL
mL
mL

ConstantNo.
1Size
20
Blank
0
Molarity
0.1
Factor
1.005
K
40.0
L
0Unit
g/L
Formula(VA-VB)*K*F*M/S
Decimal Places
4Auto In Pram.

mL
mL
mol/L

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

4090332400.05

sec
mVsec
mV

mLNone(2) Measurement condition of sodium hydrogen carbonate
Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mLT Timer
D.P. mLEnd Sens
Over mL
Max.Vol.

2Auto1
1pH00001000
0.5
20sec
mLsec
mL
mL
mL

ConstantNo.
SizeBlank
Molarity
FactorKL
Unit
Formula

220 mL0 mL
0.1 mol/L
1.005
105.990g/L(D-B)*K*F*M/S
Decimal Places
4Auto In Pram.
None*Some measurement would not be possible depending on optional configuration of system.

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

4090332400.05

sec
mV
sec
mV

mL

Measurement results
Measurement results of sodium hydroxide
Number ofMeasurement

Size(mL)

Titrant Volume(mL)Concentration
(g/L)

12320
2020

2.481
2.476
2.474
Avg.
SD
RSD

0.36140.35880.35860.360 g/L
0.0016 g/L
0.43 %

Statistic calculation

Measurement results of sodium hydrogen carbonate
Number ofMeasurement

Size(mL)

Titrant Volume(mL)Concentration(g/L)

123202020

0.683
0.691
0.690
Avg.
SDRSD

0.36380.36800.36750.366 g/L
0.0023 g/L
0.63 %

Statistic calculation

Example of titration curve

5. Note(1) Titration of sodium carbonate
Sodium carbonate was directly titrated with the hydrochloric acid standard solution in this report. There isanother method to titrate the barium carbonate generated by the addition of barium chloride in advance. Thismethod is useful to determine low concentration of sodium carbonate, the inflection point for the carbonate
become single on the titration curve. (First inflection point comes from only sodium hydroxide, and second
inflection point comes from only sodium carbonate (barium carbonate).) However, this method is unsuitable todetermine the high concentration of sodium carbonate because the precipitation amount of barium carbonate
increases and the titration speed gets slow.
(2) Environment for titration
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 decreases, while it
increases 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 of nitrogen gas also has a positive effect.
Keywords: Sodium hydroxide, Sodium carbonate, Fractional titration, Neutralization titration*Some measurement would not be possible depending on optional configuration of system.