Question

Find the theoretical oxygen demand for the

followingsolutions?
a. 200mg/L of acetic acid, CH3COOH.
b. 30mg/L of ethanol, C2H5OH.
C. 50mg/L of sucrose C2H12O6.

Answer 1

a) 213.3 mg/L

b) 62.61 mg/L

c) 0.0225 mg/L

Step-by-step explanation:

Theoretical oxygen demand (ThOD)is essentially the amount of oxygen required for the complete degradation of a given compound into the final oxidized products

a) Given:

Concentration of acetic acid,
`[CH3COOH]` = 200 mg/L

`CH3COOH + 2O2 \rightarrow 2CO2 + 2H2O`

`ThOD = (mass\ O2)/(mass\ CH3COOH) * conc. CH3COOH`

Based on the reaction stoichiometry:

mass of
`CH3COOH` = 60 g

mass of
`O2`= 2(32) = 64 g

`ThOD = (64 g)/(60 g) * 200mg/L = 213.3 mg/L`

b) Given:

Concentration of ethanol,
`[C2H5OH]` = 30 mg/L

`C2H5OH + 3O2 \rightarrow 2CO2 + 3H2O`

`ThOD = (mass\ O2)/(mass\ C2H5OH) * conc. C2H5OH`

Based on the reaction stoichiometry:

mass of
`C2H5OH` = 46 g

mass of
`O2`= 3(32) = 96 g

`ThOD = (96 g)/(46 g) * 30mg/L = 62.61 mg/L`

c) Given:

Concentration of sucrose,
`[C12H22O11]` = 50 mg/L

`C12H22O11 + 12O2 \rightarrow 12CO2 + 11H2O`

`ThOD = (mass\ O2)/(mass\ C22H22O11) * conc. C12H22O11`

Based on the reaction stoichiometry:

mass of
`C12H22O11` = 342 g

mass of
`O2`= 12(32) = 384 g

`ThOD = (384 g)/(342 g) * 50mg/L = 0.0225 mg/L`