HIRANUMA APPLICATION DATA

Data No.

Automatic Titrator

H4Apr. 13,
2022

Determination of available chlorine insodium hypochlorite

SODA PULP
INDUSTRY
1. Abstract

Sodium hypochlorite is used for bleaching and sterilization of tap water because of its strong oxidizing
and disinfecting properties. Sodium hypochlorite is relatively stable at the alkaline region. However, it isunstable at the acidic region and becomes hypochlorous acid (HClO). It oxidizes water and generates chlorine(Cl2). The concentration of available chlorine has to be measured regularly because sodium hypochloritedegrades slowly and generates sodium chloride.
This report introduces an example for determination of available chlorine as follows:.
1) Add potassium iodide to sodium hypochlorite to generate free iodine.
2) Titrate the free iodine generated from the reaction (1) with sodium thiosulfate to determine availablechlorine (2) by redox titration.

→

Cl2+2KI

I2+2Na2S2O3→

I2+2KCl………

(1)

2NaI+Na2S4O6 ………

(2)

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

Hiranuma Automatic Titrator COM series

Electrodes：

Platinum electrodePT-301：

Reference electrodeRE-201Z※Instead of above electrodes, the following electrodes are usable.
・PR-701BZ (Platinum reference combination electrode)・Combination of PT-301 (Platinum Electrode) and GR-501BZ (Glass referenceelectrode)<Remark> Measurement of alkaline component in sodium hypochlorite will bepossible with the combination of PT-301 and GR-501BZ.
(2) Regents
Titrant：0.3 mol/L Sodium thiosulfate standard solution

Additive solution：10 mL of 20% potassium iodide solution

Buffer solution：10 mL of 50 % acetic acid solution3. Measurement procedure(1) Dispense 2 mL of sample and accurately weigh it.
(2) Add about 10 mL of 20 % potassium iodide solution.
(3) Add about 30 mL of DI water.
(4) Add about 10 mL of 50 % acetic acid solution.
(5) Immerse electrodes and titrate with 0.3 mol/L sodium thiosulfate standard solution.

4. Measurement conditions and results
Example of titration conditions
Cnd. No.
MethodBuret No.
Amp No.
D.UnitS- Timer
C.P. mL
T.Timer
D.P. mLEnd Sens
Over mLMax Vol.

1Auto12mV
15000200120sec
mL
sec
mL
mL
mL

Constant No.
1Size
0Blank0Morality
0.3
Factor
1.013
K35.45
L0Unit%Formula(D-B)*K*F*M/(S×10)
Decimal Places
4Auto input parameter

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

g
mL
mol/L

50503
3
2400.05

sec
mV
sec
mV

mL

None

Measurement results
Number ofSize

Titrant

Concentration

Measurement(g)

Volume (mL)(%)

12.612330.71012.6650

22.5984

30.52812.6572

32.5988

30.572

12.6735

Avg.

12.67 %SD

0.01 %

RSD

0.06 %

Statisticcalculation

Example of titration curve

5. NotePlease refer to the following points to improve the measurement accuracy.
1) Weigh a sample size quickly because available chlorine is unstable.
2) Titrate free iodine immediately because the iodine generated by addition of potassium iodide readily
volatilizes.
Addition of plenty potassium iodide is required because the volatilization of iodine depends on theconcentration of the added potassium iodide.
Keywords: Sodium hypochlorite, Available chlorine, Redox titration*Some measurement would not be possible depending on optional configuration of system.