Question

Caproic acid (responsible for the odor of dirty socks) is composed of C, H and O, Combustion analysis of a 0.225 gram sample produces 0.512 g CO2 and 0.209 g H2O. what is its empirical formula? (b) Caproic acid has a molar mass of 116 g/mol. What is its molecular formula?

Answer 1

Mass C in 0.512g CO2
Molar mass CO2 = 44.009 g/mol
Molar mass C = 12.011 g/mol
Mass C = 12.011/44.009*0.512 = 0.1397g C

Mass H in 0.209g H2O
Molar mass H2O = 18.0015g/mol
Molar mass H = 1.008: H2 = 2.016
Mass H = 2.016/18.0015*0.209 = 0.0234g H

Mass of O = 0.225 - ( 0.1397 + 0.0234) = 0.0619g O

Divide through by respective atomic mass:
C = 0.1396/12.011 = 0.01162
H = 0.0234/1.008 = 0.0232
O = 0.0619/15.999 = 0.00387

Divide through by smallest:
C = 0.0116/0.00387 = 2.0998 = 3
H = 0.0232/0.00387 = 5.99 = 6
O = 1

Empirical formula = C3H6O

Molar mass = 58g/mol

Molar mass of compound = 116g/mol : 116/58 = 2

Molecular formula = ( C3H6O)2 = C6H12O2