The company you work for plans to release a waste stream containing 7 mg/L

Question

of benzaldehyde . Assuming that benzaldehyde degrades according to the reaction:
C7H6O + 8O2 → 7CO2 + 3H2O
Calculate the theoretical carbonaceous oxygen demand of this waste stream in mg/L.

Answer 1

Molecular Weights:
C7H6O = 106g/mol = 106mg/mmol
O2 = 32g/mol = 32mg/mmol

Stoichiometry Demand:
8 moles of O2 are needed per 1 mole of C7H6O

Therefore:
(8mol-O2)/(1mol-C7H6O) * (32g/mol)/(106g/mol) * 7mg/L

All units will cancel except mg/L:
8*(32/106)*7 = 16.906 mg/L