GATE 2020 CE (CE2) – Question 64

Water and Waste Water Quality and Treatment · Water quality standards, parameters and water quality index · 2 marks · Numerical answer

Water contains $C_8H_{16}O_8$ at $10^{-3}$ mol/L. Atomic weights C = 12, H = 1, O = 16. Find theoretical oxygen demand (g O₂/L), to two decimals.

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Correct answer: .24 to .27

Explanation

Complete oxidation is $C_8H_{16}O_8+8O_2\to8CO_2+8H_2O$. Each mole requires $8(32)=256$ g O₂. At 0.001 mol/L demand is 0.256 g/L, or **0.26 g/L**.