Question

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.

Answer 1

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`

                            = 784ppm
Hence the COD value is 784 ppm.