Question

2 points
Q.10 A 50 ml of sewage water
sample was refluxed with 0.1N
of K2Cr2O7 in presence of
H2SO4 and Ag2SO4 and after
refluxing unreacted dichromate
required 5 ml of 0.1 N FAS
solution. A blank titration
required 15 ml of 0.1 N FAS
solution. Calculate the COD of
sewage water.​

Answer 1

Answer:

The COD of sewage water is 160 mg/

Explanation:

COD (Chemical Oxygen Demand) is a measure of the amount of oxygen required to oxidize the organic matter present in a sample of water.

To calculate the COD of sewage water based on the information given in the question, we can use the following formula:

COD = $\frac{V1,V2,N}{V}$

where,

V1 = volume of FAS solution required for blank titration = 15 ml

V2 = volume of FAS solution required for sewage water sample = 5 ml

N = normality of FAS solution = 0.1 N

V = volume of sewage water sample taken for refluxing = 50 ml

Substituting the values in the formula, we get:

COD = $\frac{(5-15) x 0.1 x 8000 }{50}$

= $\frac{(-10) x 0.1 x 8000 }{50}$

= 160 mg/L

Therefore, the COD of sewage water is 160 mg/L.

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