Question

A 5.05 g sample of a compound that contains only carbon, hydrogen, and oxygen was combusted, yielding 11.69 g CO2 and 2.392 g H2O. What is the lowest possible molar mass for this compound?

A) 50 g/mol
B) 75 g/mol
C) 100 g/mol
D) 125 g/mol

Answer 1

The lowest possible molar mass of a compound containing carbon, hydrogen, and oxygen is found by determining the empirical formula from the masses of carbon and hydrogen obtained from combustion products, then assuming the empirical formula weight is the molecular weight.

Step-by-step explanation:

The lowest possible molar mass for a compound consisting only of carbon, hydrogen, and oxygen can be deduced using the data from the combustion products. The mass of carbon can be found by converting the mass of CO2 to moles and then to grams of carbon. Similarly, the mass of hydrogen can be found by converting the mass of H2O to moles and then to grams of hydrogen. Subtracting the total mass of carbon and hydrogen from the sample provides the mass of oxygen. With the masses of all three elements known, the empirical formula of the compound can be determined, which gives the empirical formula weight.

To find the lowest possible molar mass, we assume that the empirical formula of the compound is also its molecular formula. Since the actual molecular mass will be an integer multiple of the empirical mass, we can divide the actual mass of the sample by the empirical mass to get the closest integer value, giving us the simplest molecular formula and the lowest molar mass.