A water sample from the Olinda Creek was subjected to analysis by gas chromatogr

Question

A water sample from the Olinda Creek was subjected to analysis by gas chromatography (GC) and was found to contain 0.453 g/L of 2,4 - dimethylphenol ((CH3)2C6H3OH).

(Relative molar mass of 2,4 - dimethylphenol = 122.16 g/mol)

Write a balanced chemical equation to describe the complete oxidation of 2,4 - dimethylphenol in the water sample.

(CH3)2C6H3OH + H2O-> (CH3)2C6H2O2 + H2O   ( this is my answer please check )

(ii) Calculate the theoretical Chemical Oxygen Demand of 2,4dimethylphenol on this water sample and express the final answer in mg/L. (Note: Marks will be given for the clear and logical layout of calculations, and the final result)

(iii) Discuss whether the value calculated in (ii) represents the likely BOD of water from the Olinda Creek? Give reasons to support your response.

Explanation / Answer

(i) Comlete oxidation of 2,4-dimethylphenol (2,4-DMP) yields acetic acid and CO2

The chemical equation is thus as shown below,

2 C8H10O + 10 O2 = 5 CH3COOH + 6 CO2

(ii) The theoretical O2 demand for this reaction would be,

2 moles of 2,4-dimethylphenol requires 10 moles of O2

We have, 0.453 g/L of 2,4-dimethylphenol in the sample

moles of 2,4-DMP = g/molar mass = 0.453/122.16 = 0.00371 mols/L = 0.00371 mols

So, the moles of O2 required would be = 0.00371 x 10/2 = 0.0185 mols

g of O2 required = 0.0185 x 32 = 0.592 g or 592 mg/L

thus, 592 mg/L is the theoretical oxygen demand.

(iii) The value calculated in (ii) represents the likely BOD of water. The value thus calculated falls under the range of the allowed uptake of 2,4-dimethylphenol in drinking water.

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