HIRANUMA APPLICATION DATA

Data No.

Automatic Titrator

H6Apr. 5,
2019

Determination of sodium chloride insodium hypochlorite

SODA PULP
INDUSTRY
1. Abstract

Sodium hypochlorite is produced by having sodium hydroxide absorb chlorine gas. Produced sodium
hypochlorite contains residual alkali (sodium hydroxide, sodium carbonate) and sodium chloride generated by thedegradation of hypochlorous acid. The residual alkali is determined by neutralization titration, and sodium
chloride is determined by precipitation titration. This report introduces an example of the determination forsodium chloride in the sodium hypochlorite with potentiometric titration as the following procedure: the titration
for the total chlorine component (sodium hypochlorite + sodium chloride) is performed first. After that, sodium
hypochlorite (available chlorine) is titrated by another method. Finally, sodium chloride is determined by thesubtraction of sodium hypochlorite from the total chloride component.
The total sodium chloride (total chloride component) is determined according to the following formula (1)and (2): add hydrogen peroxide into a sample to degrade sodium hypochlorite, and generate sodium chloride as
described in formula (1). Titrate with nitric acid standard solution until the pH goes down to 2 ~ 3. After thesolution is acidified, determine the total sodium chloride with silver nitrate standard solution by precipitation
titration as formula (2).

NaClO
NaCl++H2O2→
AgNO3 →NaCl
AgCl+ H2O ++ NaNO3

O2…………
………………

(1)(2)

Regarding the determination of available chlorine, free iodine generated by the addition of potassium
iodide as described in formula (3) is determined with sodium thiosulfate standard solution by redox titration asshown in formula (4).
H2O →I2 +NaCl +→2NaI+ Na2S4O6

NaClO +2 KI +I2

2 Na2S2O3+…………
………………

2KOH

2. Configuration of instruments and reagents(1) Configuration
Main unit ：Option：

Hiranuma Automatic Titrator COM series
One buret, one buret head

Electrodes： <For total sodium chloride>
Glass electrodeGE-101B

Silver combination electrode

AGR-811Z (Double junction type)<For available chlorine>
Platinum electrodePT-301

Reference electrodeRE-201Z

(3)(4)

(2) Reagents<For total sodium chloride>
Titrant：0.2 mol/L Silver nitrate standard solution,0.1 mol/L Nitric acid standard solution

Additive：3 % Hydrogen peroxide solution<For available chlorine >Titrant：0.2 mol/L Sodium thiosulfate standard solution

Additive：10 % Potassium iodide solution
2 mol/L Acetic acid solution

3. Measurement procedure(1) Measurement for total sodium chloride(i) Dispense 0.5 mL of sample into a 100 mL beaker with micropipette.
(ii) Add 50 mL of DI water.
(iii) Add 5 mL of 3 % hydrogen peroxide solution and degrade sodium hypochlorite.
(iv) Immerse the electrodes (GE-101B/AGR-811Z) into sample solution.
Titrate with 0.1 mol/L nitric acid standard solution and adjust the pH to 2 ~ 3.
(v) Titrate with 0.2 mol/L silver nitrate standard solution.
(2) Measurement for available chlorine(i) Dispense 0.5 mL of sample into a 100 mL beaker with micropipette.
(ii) Add 50 mL of DI water.
(iii) Add 1 mL of 10 % potassium iodide solution.
(iv) Add 10 mL of 2 mol/L acetic acid solution.
(v) Immerse electrodes (PT-301/RE-201Z) and titrate with 0.2 mol/L sodium thiosulfate standard solution.

4. Measurement conditions and results
Examples of titration conditions(1) Measurement for total sodium chloride(i)Titration with 0.1 mol/L nitric acid standard solution
Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mL
Direction
T Timer
D.P. mL
End Point
Over mL
Max.Vol.

1Set
11pH
50↓
00
3.0
0.0
20

sec
mL
sec
mL
pH
mL
mL

ConstantNo.
SizeBlank
Molarity
FactorKL
Unit
FormulaDecimal PlacesAuto In Pram.

10.5 mL0 mL
0.1 mol/L
1.004
0.000.000mLD
3Non

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

409033240sec
mVsec
mV

(ii) Titration with 0.2 mol/L silver nitrate standard solutionCndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mLT Timer
D.P. mLEnd Sens
Over mL
Max.Vol.

2Auto
22mV
5000100
0.220sec
mL
sec
mL
mL
mL

ConstantNo.
SizeBlank
Molarity
FactorKL

20.5 mL0 mL
0.2 mol/L
1.000
58.44
0.000

Unit
FormulaDecimal Places
Auto In Pram.

%(D-B)*K*F*M/(S*10)
4Non

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

805053240sec
mV
sec
mV

(2) Measurement for available chlorine (Calculation of sodium chloride concentration)(i)Titration with 0.2 mol/L sodium thiosulfate standard solution
Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mLT Timer
D.P. mLEnd Sens
Over mL
Max.Vol.

3Auto
12mV
50002000.3
20sec
mL
sec
mL
mLmL

ConstantNo.
SizeBlank
MolarityFactorKL

30.5 mL
0 mL
0.2 mol/L
1.002
35.45
0.000

Unit
FormulaDecimal Places
Auto In Pram.

%(D-B)*K*F*M/(S*10)
4Non

Mode No.
Pre Int
Del K
Del Sens
Int Time
Int Sens
Brt Speed
Pulse(ii) Calculation of sodium chloride concentration
Cndt No.
Method4
Calc

ConstantNo.
SizeBlank
Molarity
Factor
KL

40.5
00.20
14.80
0.8243

Unit
FormulaDecimal Places
Auto In Pram.

%
K-CA*L
4mL
mLmol/L※1※2Non※1

Input the result of total sodium chloride.

※2

Conversion coefficient from available chlorine to sodium chloride (58.44(NaCl)/70.9(Cl 2))505033240

secmVsecmV

Measurement results(1) Results of total sodium chloride
Number ofSize

Titrant

Total sodium chloride

Measurement(mL)

Volume (mL)Concentration (%)

1

0.5

6.329

14.795

2

0.5

6.324

14.783

30.5

6.339

14.818

Statistic
calculation

Avg.

14.80 %

SD

0.02 %

RSD

0.12 %(2) Results of available chlorine (Calculated results of sodium chloride concentration)
Number ofSize

Titrant

Available chlorineSodium chloride

Measurement(mL)

Volume (mL)Concentration (%)

Concentration (%)

1

0.5

10.17414.456

2.884

20.5

10.223

14.525

2.827

30.5

10.27614.601

2.765

Average

14.52 %

2.83 %

Standard deviation

0.07 %

0.06 %

Coefficient of variation

0.50 %

2.11 %

Statistic
calculation

Measurement for total sodium chloride

Measurement for available chlorine

Examples of titration curves

5. Note
1) Measurement for total sodium chloride
Residual sodium hypochlorite could cause measurement error. Addition of excess hydrogen peroxide isrequired to degrade sodium hypochlorite completely.
2) Measurement for available chlorine
The following tips can improve measurement accuracy.
i) Weigh a sample size quickly because available chlorine is unstable.
ii) Titrate free iodine immediately because the iodine generated by addition of potassium iodide is easy tovolatilize. Addition of plenty potassium iodide is required because the volatilization of iodine depends onthe concentration of added potassium iodide.
Keywords: Sodium hypochlorite, Sodium chloride, Residual alkali, Available chlorine, Precipitation titration*Some measurement would not be possible depending on optional configuration of system.