Question

500 ml of a sample of water required 19.6 mg of k2cr2o7 for the oxidation of dissolved organic matter in it in the presence of h2so4. The cod of water sample is

Answer 1

COD determines the quantity of oxygen required to oxidize the organic matter in water ... The organic matter present in the sample gets oxidized completely by potassium dichromate (K2Cr207) in the presence of sulphuric acid (H2SO4), silver

Answer 2

The chemical oxygen demand for the water is 6.4 ppm.

Given:

500 ml of sample water

19.6 mg of$\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}$

To find:

The COD of the water sample.

Solution:

Chemical oxygen demand is the total amount of oxygen required to chemically oxidise the biodegradable and non biodegradable organic matter.

From the given,

Required weight of $\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}$= 19.6 gm.

Volume of water = 500 ml

Number of gram equivalents of dichromate reacts is  equal to the number of gram equivalents of oxygen required.

gram equivalent of oxygen = 8

$X factor of \mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7} = 6$

$\frac{19.6 \times 2}{\frac{294.2}{6}}=\left(\frac{\text {weight}}{8}\right)$

Weight of oxygen demand=6.4 mg/lit  

ppm=6.4