Question

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 . 

Answer 1

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.