A 10ml of sample of waste water was refluxed with 20ml of potassium dichromate solution and after refluxing the excess unreacted dichromate required 36.2ml of 0. 1M FAS solution. A blank of 1Om/ of distilled water on refluxing with 20ml of dichromate solution required 46ml of 0. 1M FAS solution. Calculate the COD value of waste water.
Given data :- Vb = 46ml Vt = 36.2ml
N = 0.1M Ve = 10ml
To find:- COD
Solution :- `COD = ((Vb-Vt) xx "Normality" xx 8000)/Ve`
`=(( 46-36.2) xx 0.1 xx 8000)/10`
Hence the COD value is 784 ppm.