Question

6ml of waste water was refluxed with 25ml ofK₂Cr₂ O₇ solution and after refluxing the excess unreacted dichromate required 20ml of 0. 1 N FAS solution. A blank of distilled water on refluxing with 25 ml of K₂Cr₂O₇ solution required 35ml of 0. 1 N FAS solution . Calculate the COD of the waste water sample.

Answer 1

Given data:-            Vb=35mI,                Vt=20ml,

                                N=O. 1N,                  Y=6ml.

To find:-                  COD{Chemical Oxygen Demand).

Formula:-               `COD = ((Vb - Vt) xx N xx 8000)/(Y)` mg/L

Solution:-               `COD = ((35-20) xx 0.1 xx 8000)/6` mg/L

                               COD = 2000mg/L