100 ml of a sample of water requires 1.96 mg of potassium dichromate in the presence of 50% `H_2SO_4` for the oxidation of dissolved organic matter in it. Calculate the chemical oxygen demand.

Explanation

One gram equivalent of any oxidant can give, one equivalent weight of oxygen (8 g)
`49 g K_2Cr_2O_7 to 8g " Oxygen"`
` 1.96 xx 10^(-3) g K_2Cr_2O_7 to (8 xx 1.96 xx 10^(-3))/(49)=0.32 mg `
Chemical oxygen demand of the given 100 ml sample of water `=(0.32)/(0.1) = 3.2 ppm`