Final answer:
Chemical formulas are based on the empirical formulas that are determined by measuring the mass of each element in a compound and converting these masses to moles.
Step-by-step explanation:
Prescription formulas or chemical formulas are based on the method of determining a compound's empirical formula by measuring the masses of its constituent elements and then converting those masses into molar amounts. These molar amounts are then used to compute whole-number ratios that lead to the derivation of the empirical formula.
For example, if a compound is found to contain 1.71 g C (carbon) and 0.287 g H (hydrogen) these masses will first be converted to moles, which represent the number of atoms in the sample and then used to create a ratio that reflects the simplest whole-number ratio of atoms in the compound.