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JIPMER 2015
Exam
JIPMER
Year
2015
Subject
Chemistry
Chapter
Environmental Chemistry

JIPMER 2015 · Chemistry · Environmental Chemistry

500 mL of a sample of water required 19.6 mg of K_2 Cr_2 O_7 for...

500 mL of a sample of water required 19.6 mg of K2Cr2O7\mathrm{K}_2 \mathrm{Cr}_2 \mathrm{O}_7 for the oxidation of dissolved organic matter in it in the presence of H2SO4\mathrm{H}_2 \mathrm{SO}_4. The COD of water sample is

Options

  1. A3.2 ppm
  2. B7.2 ppm
  3. C6.4 ppm
  4. D4.6 ppm

Correct answer

C. 6.4 ppm

Step-by-step solution

500mLHH2O⟶19.6×10−3gK2Cr2O7106mLH2O⟶39.2gK2Cr2O749g of K2Cr2O7⟶8g of O239.2g of K2C2O7⟶6.4g of O2∴ COD =6.4ppm\begin{aligned} & 500 \mathrm{ mL} \mathrm{H} \mathrm{H}_2 \mathrm{O} \longrightarrow 19.6 \times 10^{-3} \mathrm{ g} \mathrm{ K}_2 \mathrm{Cr}_2 \mathrm{O}_7 \\ & 106 \mathrm{ mL} \mathrm{H}_2 \mathrm{O} \longrightarrow 39.2 \mathrm{ g} \mathrm{ K}_2 \mathrm{Cr}_2 \mathrm{O}_7 \\ & 49 \mathrm{ g} \text{ of } \mathrm{K}_2 \mathrm{Cr}_2 \mathrm{O}_7 \longrightarrow 8 \mathrm{ g} \text{ of } \mathrm{O}_2 \\ & 39.2 \mathrm{ g} \text{ of } \mathrm{K}_2 \mathrm{C}_2 \mathrm{O}_7 \longrightarrow 6.4 \mathrm{ g} \text{ of } \mathrm{O}_2 \\ & \therefore \quad \text{ COD }=6.4 \mathrm{ppm} \\ & \end{aligned}
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