Final answer:
To find the number of atoms based on an empirical formula, calculate the empirical formula mass, divide the molecular mass by this value to find a multiplication factor (n), then multiply each subscript in the empirical formula by n to get the molecular formula.
Step-by-step explanation:
To calculate the number of atoms from an empirical formula, you must first understand the relationship between the empirical and molecular formulas. The empirical formula provides the simplest whole-number ratio of atoms in a compound, whereas the molecular formula gives the actual number of atoms of each element in a molecule of the compound. Here is how you can find the number of atoms using the empirical formula and the molar mass of the compound:
- Calculate the empirical formula mass (EFM), which is the sum of the average atomic masses for all atoms represented in the empirical formula.
- Divide the molar mass of the compound by the empirical formula mass. The result is a whole number or very close to it, which is the multiplier (n).
- Multiply the subscripts in the empirical formula by n to get the molecular formula, and thus the actual number of atoms of each element.
For example, if a compound's empirical formula is CH₂O and its molecular mass is 180 amu, you would first find the EFM (30 amu) and then divide the molecular mass by the EFM (180 amu / 30 amu = 6), which tells you the molecular formula contains six times the atoms in the empirical formula (C₆H₁₂O₆).