Determine the mass of oxygen used for the complete combustion of fatty acid. And Balance the above chemical equation.

Question

Fatty acids are one of the basic building blocks of humans. They have a general formula

of CxHyOz. A technician wants to determine the type of pure fatty acid isolated from a

metabolite mixture. As 16.71g of the pure fatty acid is fully combusted under oxygen

(O2), it decomposes according to the below chemical equation.

fC_xH_yO_z(l)+gO₂(g)-->hCO₂(g)+jH₂O(l)

It is found that only 46.33g carbon dioxide (CO2) and 16.43g water H2O(l) were

obtained as the products. It is also known that the molecular weight of the fatty acid

is 238 g/mol.

1.Balance the above chemical equation.

2.Determine the mass of oxygen used for the complete combustion of fatty acid.

Answer 1

moles C = 46.33 g CO2 x 1 mol CO2/44 g x 1 mol C/ mol CO2 = 1.053 mols C (x 12g/mol = 12.64 g C)

moles H = 16.43 g H2O x 1 mol H2O/18 g x 2 mol H/mol H2O = 1.826 mols H (x 1g/mol = 1.826 g H)

grams O = 16.71 g - 12.64 g - 1.826 g = 2.244 g O x 1 mol/16 g = 0.140 mols O

Divide all by 0.140 to try to get whole numbers:

7.5 mols C

13 mols H

1 mol O

Multiply all by 2 to get whole numbers

15 mols C

25 mols H

2 mols O

Empirical formula = C₁₅H₂₅O₂

molar mass C₁₅H₂₅O₂ = 237 g/mol

Since this is same as molar mass of the unknown fatty acid, the identity of the unknown is C₁₅H₂₅O₂

1). Balanced equation: 4C₁₅H₂₅O₂ + 81O₂ <==> 60CO₂ + 50H₂O

2). 16.71 g FA x 1 mol/238 g x 81 mol O₂ / 4 mol FA x 32 g O2/ mol = 45.50 g O₂