Question

The chemical oxygen demand can be given as __________

(a) {[(V1-V2)*N*8]}/x

(b) {[(V1+V2)*N*8]}/x

(c) {[(V2-V1)*N*8]}/x

(d) {[(V1/V2)*N*8]}/x

I had been asked this question during an online interview.

My query is from Problems, Units and Formulae topic in portion Water of Applied Chemistry

Answer 1

Right choice is (a) {[(V1-V2)*N*8]}/x

The explanation: The chemical oxygen demand can be given by {[(V1-V2)*N*8]}/x where V1=volume of ferrous ammonium sulphate required for blank, V2=volume of ferrous ammonium sulphate required for test, N=normality of ferrous ammonium sulphate, x=volume of sewage sample taken.