To determine empirical formula from percent composition, which data is essential?

To determine empirical formula from percent composition, which data is essential?

• A. Relative atomic masses
• B. Molar volume
• C. Boiling point
• D. Density

Answer: (A)

From percent composition you have masses of each element in a sample. To turn that into an empirical formula you must compare how many moles of each element are present, not just their masses. This requires converting the masses to moles, which is done by dividing each mass by the element’s relative atomic mass. Once you have the mole amounts, you find the smallest whole-number ratio to get the empirical formula. So, relative atomic masses are essential because they let you convert mass to moles. Molar volume, boiling point, and density don’t provide the needed mole information from percent composition, so they aren’t used to determine the empirical formula.

From percent composition you have masses of each element in a sample. To turn that into an empirical formula you must compare how many moles of each element are present, not just their masses. This requires converting the masses to moles, which is done by dividing each mass by the element’s relative atomic mass. Once you have the mole amounts, you find the smallest whole-number ratio to get the empirical formula. So, relative atomic masses are essential because they let you convert mass to moles.

Molar volume, boiling point, and density don’t provide the needed mole information from percent composition, so they aren’t used to determine the empirical formula.