Question 1

What is the difference between empirical and molecular formulas?

Accepted Answer

The empirical formula gives the simplest whole-number ratio of atoms in a compound (e.g., CH₂O), while the molecular formula gives the actual number of atoms per molecule (e.g., C₆H₁₂O₆ for glucose). The molecular formula is always a whole-number multiple of the empirical formula. Some compounds have the same empirical and molecular formula (e.g., H₂O, CO₂).

Question 2

How do I find the empirical formula from percent composition?

Accepted Answer

Convert each element's mass percentage to grams (assume 100 g sample), divide each by its atomic mass to get moles, then divide all mole values by the smallest to get the simplest ratio. If the ratios are not close to whole numbers, multiply all by the smallest integer that gives whole numbers.

Question 3

Why might the multiplier not be exactly a whole number?

Accepted Answer

Experimental molar mass measurements always have some degree of uncertainty. The raw ratio (experimental mass / empirical mass) may be something like 5.93 or 6.08 instead of exactly 6. The calculator rounds to the nearest whole number. If the ratio is far from any integer (e.g., 3.5), it may indicate an error in the empirical formula or experimental molar mass.

Question 4

Can this calculator handle elements besides C, H, O, N, and S?

Accepted Answer

This calculator supports the five most common organic elements: carbon, hydrogen, oxygen, nitrogen, and sulfur. For compounds containing other elements (halogens, phosphorus, metals), you would need to calculate the empirical formula mass manually and use the same principle: n = experimental mass / empirical mass.

Molecular Formula Calculator

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