The empirical formula of a compound is \(\mathrm{CH}\). If the molar mass of this compound is about \(78 \mathrm{~g}\), what is its molecular formula?

The empirical formula of a compound signifies the simplest whole-number ratio of atoms of each element present in the compound. It is a representation of the relative number of atoms, not the actual number of atoms as in a molecular formula. For example, for a compound with an empirical formula of CH, it means that for every one carbon atom, there is one hydrogen atom.

This basic building block provides a foundation for understanding the composition of the molecule but does not convey information about its actual molecular size or structure. To determine the empirical formula, one typically starts by finding the percent composition of each element in a compound and then uses these percentages to calculate the smallest ratio of atoms.

Calculating the molar mass of a compound is a vital step in chemistry that informs us about the mass of one mole of that substance. It can be computed by summing the atomic masses of all atoms in the molecule as represented by its empirical or molecular formula. For instance, to find the molar mass of the empirical formula CH, we add the atomic mass of carbon (approximately 12 g/mol) with the atomic mass of hydrogen (approximately 1 g/mol), resulting in a molar mass of 13 g/mol for the empirical formula unit.

Steps to Calculate Molar Mass:

• Identify the atoms present in the chemical formula.
• Find the atomic mass of each atom from the periodic table.
• Multiply the atomic mass of each atom by its respective number in the formula.
• Sum all the individual masses to get the total molar mass of the compound.

To discern the molecular formula, which indicates the actual number of atoms of each element in a molecule, we must have both the empirical formula and the molecular weight or molar mass of the compound. The ratio of the molar mass of the compound to the mass of the empirical formula allows us to scale up the empirical formula to the molecular formula.

Process of Determining the Molecular Formula:

• Calculate the mass of the empirical formula using atomic weights.
• Divide the molar mass of the compound by the mass of the empirical formula to find the multiplication factor.
• Multiply the subscripts in the empirical formula by this factor to obtain the molecular formula.

For example, with a compound that has an empirical formula of CH and a molar mass of 78 g/mol, we find that the molar mass is 6 times the empirical formula mass. Therefore, the molecular formula is obtained by multiplying each element in the empirical formula by 6, producing C6H6.