Question

A compound contains 65.2% carbon, 13.1% hydrogen and 34.7% oxygen. If its molar mass is 208.0 g/mole, what is its molecular formula?

Answer 1

To determine the molecular formula of the compound, the percentages are converted to grams assuming a 100 g sample, followed by calculating moles for each element. The simplest ratio of these moles gives the empirical formula, which is then scaled up to match the molar mass, resulting in the molecular formula.

Step-by-step explanation:

To determine the molecular formula of a compound with a given percentage composition and molar mass, we first calculate the empirical formula and then use the molar mass to find the actual number of each kind of atom in the molecular formula.

1. Assuming 100 g of the compound, convert percentages to grams: 65.2 g of carbon, 13.1 g of hydrogen, and 34.7 g of oxygen.
2. Divide the masses by the respective atomic masses to get moles: moles of C = 65.2 g / 12.01 g/mol, moles of H = 13.1 g / 1.008 g/mol, moles of O = 34.7 g / 16.00 g/mol.
3. Divide by the smallest number of moles to get the simplest whole number ratio.
4. To get the molecular formula, divide the compound's molar mass by the empirical formula's molar mass. Multiply the atoms in the empirical formula by this ratio to get the molecular formula.

In this case, we would find the empirical formula, then determine that the molecular formula contains a certain number of carbon (C), hydrogen (H), and oxygen (O) atoms by scaling the empirical formula such that its molar mass matches the given molar mass of 208.0 g/mole.