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Peroxyacylnitrate, often abbreviated as PAN, is a significant component of photochemical smog, which commonly affects urban areas. This compound is made up of carbon, hydrogen, nitrogen, and oxygen atoms.
PAN is known for its harmful effects on human health and the environment, primarily due to its ability to irritate the eyes and respiratory system. It is a secondary pollutant, meaning it forms in the atmosphere from reactions between primary pollutants like nitrogen oxides (NOx) and volatile organic compounds (VOCs).
Understanding PAN's chemical composition is key to understanding its behavior and impact. In the context of chemistry, it can be represented by its empirical and molecular formulas, which provide insights into its structure and reactivity.

Percent composition is an important concept in chemistry that describes the relative abundance of each element within a compound. It tells us how much of the compound's mass is made up by each element, expressed as a percentage. This is crucial for understanding the makeup of compounds like peroxyacylnitrate.
To find the percent composition, one must first know the total mass of the compound and the masses of the individual elements. In the case of peroxyacylnitrate from the problem, given percentages provided for carbon (19.8%), hydrogen (2.50%), and nitrogen (11.6%) help determine the remainder as oxygen by mass, using the formula:
Total percent of all elements = 100%.
By subtracting the percentage totals of known elements from 100%, the remainder represents oxygen's percent composition. This calculation reveals how the elements are distributed in the compound and is a fundamental step in calculating the empirical formula.

The molecular formula of a compound tells us the exact number of atoms of each element in a molecule of the compound. While the empirical formula gives the simplest whole-number ratio of these atoms, the molecular formula delivers a more detailed view of the actual molecule.
Once you determine the empirical formula, the next step is to find the empirical formula weight. This is calculated by adding the atomic weights of each element as indicated in the empirical formula.
To derive the molecular formula of peroxyacylnitrate, compare the empirically found weight with the given molar mass of the compound (120 g/mol in the exercise). Dividing the molar mass by the empirical formula weight gives a multiplier, typically a whole number, which allows one to scale up the empirical formula to the correct molecular size.

• The empirical formula tells you the ratio of atoms.
• Molecular formula tells you the exact number of atoms.

Understanding both formulas is essential for comprehensive chemical analysis and helps clarify the substance's chemical identity and reactions.