In a COD test, 30.5 cm3 and 15.5 cm3 of 0.05 N FAS solutions are required for blank & sample titration respectively. The volume of test sample used was 25 cm3. Calculate the COD of the sample solution.

9 c]In a COD test, 30.5 cm3 and 15.5 cm3 of 0.05 N FAS solutions are required for blank & sample titration respectively. The volume of test sample used was 25 cm3. Calculate the COD of the sample solution.

GIVEN :

blank titer value = 35.5cm³ = b

back titer value = 15.5cm³= a

Normality = 0.05N

Volume of test sample = 25cm³

FORMULA :

COD = ((b – a) N × 8 × 1000) / V

COD = ((30.5 – 15.5) × 0.05 × 8 × 1000) / 25

COD = 240 mg of O₂