Question

find the theoretical oxygen demand for the following solutions:

(A) 200 mg/L of acetic acid, CH3COOH

(B) 30 mg/L of ethanol, C2H5OH

(C) 50 mg/L of glucose, C6H12O6

please show all work!

Answer 1

A) CH3COOH + 2 O2 → 2 CO2 + 2 H2O
acetic acid molar mass = 60
Thus, it takes 64 g of oxygen to oxidize 60 g of acetic acid to 2CO2 and 2H2O.
Molarity=Mol/L= (mass / molar mass) / L
0.2 M = W/60
mass =12 g
12 g of acetic acid requiring volume of oxygen = 12X(64/60) = 12.8 L of O₂
12g = 200mg/L
12.8g = 213 mg/L O₂

B) C2H5OH+ 3 O2 ----> 2 CO2 + 3 H2O
Ethanol molar mass = 46
it takes 96 g of oxygen to oxidize 46 g of ethanol to 2CO2 and 3H2O.
Molarity=Mol/L= (mass / molar mass) / L
0.03 M = mass /46
mass = 1.38 g
1.38 g of ethanol requiring volume of oxygen = 1.38(96/46)= 2.88 L of O2
1.38g = 30mg/L C2H5OH
2.88g = 62.6 mg/L O2