Numerical

A 1Oml of sample of water was refluxed with 20ml potassium dichromate solution and after refluxing the excess unreacted dichromate required 26.2ml of 0. 1M FAS solution. A blank 1Oml of distilled water on refluxing with 20ml of dichromate solution required 36ml of 0. 1M FAS solution. Calculate the COD of waste water .

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#### Solution

Given data - Vb = 36ml Vt = 26.2ml

N = 0.1M Ve = 10ml

To find:- COD

Solution :- `COD = ("(Vb-Vt) xx Normality" xx 8000)/(Ve)`

= ` ((36-26.2) xx 0.1 xx 8000)/10`

= 784ppm

Hence the COD value is 784 ppm.

Concept: COD- Definition and Significance

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