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Environment & Health

Question
2 out of 72
 

Orthotolidine test is used for detecting:


A Chlorine
B Nitrites
C Nitrates
D Ammonia

Ans. A Chlorine Ref: Park; 22nd edi, pg – 663

Orthotoluidine test enables both free and combined chlorine in water to be measured.

  1. ORTHOTOLIDINE (OT) TEST - Orthotolidine test enables both free and combined chlorine in water to be determined with speed and accuracy. The test was developed in 1918. The reagent consists of analytical grade O-tolidine, dissolved in 10 per cent solution of hydrochloric acid. When this reagent is added to water containing chlorine, it turns yellow and the intensity of the colour varies with the concentration of the gas. The yellow colour is produced by both free and combined chlorine residuals. OT reacts with free chlorine instantaneously but reacts more slowly with combined chlorine.
  2. The test is carried out by adding 0.1 ml of the reagent to 1 ml of water. The yellow colour produced is matched against suitable standards or colour discs. Commercial equipment is available for this purpose. 'It is essential to take the reading within 10 seconds after the addition of the reagent to estimate free chlorine in water. The colour that is produced after a lapse, say 15-20 minutes, is due to the action of both free and combined chlorine.

ORTHOTOLIDINE-ARSENITE (OTA) TEST - This is a modification of the OT test to determine the free and combined chlorine residuals separately. Further, the errors caused by the presence of interfering substances such as nitrites, iron and manganese all of which produce a yellow colour with o-tolidine, are overcome by the OTA test.

Environment & Health Flashcard List

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