Determine the empirical formula of the compound with the following mass percents of the elements present: \(66.63 \% \mathrm{C} ; 11.18 \% \mathrm{H} ; 22.19 \% \mathrm{O}\).

Understanding the mass percent composition is the first step in determining the empirical formula of a compound. Essentially, it tells us the percentage by mass of each element within a compound. To analyze the mass percent composition, imagine you have a 100-gram sample of the compound. This simplifies the calculation since the percentages can directly be considered as mass in grams.

For instance, if a compound has 66.63% carbon, 11.18% hydrogen, and 22.19% oxygen, it means that in a 100-gram sample, there would be 66.63 grams of carbon, 11.18 grams of hydrogen, and 22.19 grams of oxygen. This conversion from percentage to mass is vital to finding the empirical formula as it sets the stage for subsequent stoichiometric calculations.

The next concept vital for empirically determining a compound’s formula is molar mass, which represents the mass of one mole (approximately 6.022 x 10^23 particles) of a substance. The molar mass is typically expressed in grams per mole (g/mol) and is calculated using the atomic masses from the periodic table.

In our example, you would use the molar masses of carbon (12.01 g/mol), hydrogen (1.01 g/mol), and oxygen (16.00 g/mol) to convert the grams of each element into moles. This step is necessary because chemical formulas are based on mole ratios rather than mass ratios.

After determining the number of moles of each element, the next crucial step is to find the mole ratio. This ratio compares the number of moles of each element in the compound to one another. To do this, divide the number of moles of each element by the smallest number of moles from the elements analyzed.

This process, often referred to as 'normalizing,' helps to find the simplest whole number ratio of the atoms in the compound. The numbers you obtain, once simplified, will give you the mole ratio of the elements. These ratios are essential as they form the basis of the empirical formula, which is the simplest representation of a compound’s proportional elements.

Finally, we have the concept of stoichiometry, which involves the quantitative relationship among elements in chemical reactions and compositions. Using stoichiometry, we interpret the mole ratios to write the empirical formula. The empirical formula reflects the simplest integer ratio of atoms in a compound and may differ from the molecular formula, which shows the actual number of atoms in a molecule.

In our exercise, after you normalize the moles and round to the nearest whole number, you get the ratios that lead to the empirical formula C₄H₈O. Stoichiometry is the field that encompasses this entire process, illustrating how the balanced proportions of elements combine to form a specific compound.