Question 1

What is an empirical formula?

Accepted Answer

An empirical formula shows the simplest whole-number ratio of atoms in a compound. For example, glucose has a molecular formula of C₆H₁₂O₆ but an empirical formula of CH₂O (ratio 1:2:1).

Question 2

How do I find the molecular formula from the empirical formula?

Accepted Answer

Divide the known molecular mass by the empirical formula mass to get a whole number n. Multiply all subscripts in the empirical formula by n. For glucose: molecular mass (180.16) / empirical mass of CH₂O (30.026) = 6, so the molecular formula is C₆H₁₂O₆.

Question 3

What if my percentages do not add up to 100%?

Accepted Answer

If the percentages do not sum to 100%, the missing percentage often belongs to oxygen (in combustion analysis). For 3 elements, make sure all percentages sum to approximately 100% for accurate results.

Question 4

Why do I assume a 100 g sample?

Accepted Answer

Assuming 100 g makes the math simple: percentages directly become grams. 40% carbon in 100 g means 40 g of carbon. Then divide by atomic mass to get moles.

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