Measurement/Test for Residual Chlorine

◆Measurement/Test for Residual Chlorine◆

1) Starch Iodide Test

• Water sample is mixed with potassium iodide (KT).

• If blue colour complex is formed, it indicates presence of Residual chlorine.

• This blue solution is titrated with sodium Thiosulphide.

Residual chlorine = 0.3456 × Volume of sodium Thiosulphide solution used to convert blue colored complex into colorless

• This test is used for colored water only.

2) Orthotolidine Test

• The sample is mixed with orthotolidine.

• If colour of sample changes within 5 sec, its indications presence of free
chlorine.

• If colour of sample changes within 5 min, it indicates presence of combined
chlorine.

• This test is not used for colored water.