Determination of available chlorine in sodium hypochlorite | Autotitrator COM-A19 - JM Science
HIRANUMA APPLICATION DATA Automatic Titrator Data No. H4 Apr. 13,2022
SODA PULP INDUSTRY Determination of available chlorine in sodium hypochlorite

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 is unstable 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 hypochlorite degrades 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 available chlorine (2) by redox titration.

2. Configuration of instruments and Reagents

(1) Configuration of instruments
  Main unit : Hiranuma Automatic Titrator COM series
  Electrode : Platinum electrode PT-301
Reference electrode RE-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 reference electrode)
*Remark
Measurement of alkaline component in sodium hypochlorite will be possible with the combination of PT-301 and GR-501BZ.
(2) Reagent    
  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 solution

3. 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

Examples of titration conditions

Cndt No. 1
Method Auto
Buret No. 1
Amp No. 2
D. Unit mV
S-Timer 15 sec
C.P. mL 0 mL
T.Timer 0 sec
D.P. mL 0 mL
End Sens 200
Over mL 1 mL
Max.Vol. 20 mL
ConstantNo. 1
Size 0 g
Blank 0 mL
Molarity 0.3 mol/L
Factor 1.013
K 35.45
L 0
Unit %
Formula
(D-B)*K*F*M/(S*10)
Decimal Places 4
Auto input parameter None
Mode No. 5
Pre Int 0 sec
Del K 5
Del Sens 0 mV
Int Time 3 sec
Int Sens 3 mV
Brt Speed 2
Pulse 40
0.05 mL

 Measurement results

Number of

measurement

Size

(mL)

Titrant

volume(mL)

Concentration (%)

1

2.6123

30.710

12.6650

2

2.5984

30.528

12.6572

3

2.5988

30.572

12.6735

Statistic

calculation

Avg.

12.67 %

SD

0.01 %

RSD

0.06 %

 

Example of titration curve

5. Note

Please 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 the concentration of the added potassium iodide.

Keywords:

Sodium hypochlorite, Available chlorine, Redox titration

 

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

Hiranuma aquacounter autotitrator com-a19Soda pulp industry

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