Molecular Formula from Empirical
Multiply the empirical formula by a whole number.
About this topic
The molecular formula is a whole-number multiple of the empirical formula. Divide the known molar mass of the compound by the empirical formula mass to get the multiplier n, then multiply all subscripts by n. If the empirical formula is CH2O (30 g/mol) and the molar mass is 180 g/mol, n = 6 and the molecular formula is C6H12O6.
The empirical formula comes from composition data, but it cannot tell the real size of the molecule. A separate measurement of molar mass is needed, from mass spectrometry, from freezing point depression or from gas density. The ratio of molar mass to empirical mass should be very close to a whole number, such as 1, 2, 3 or 6. If not, recheck your calculations.
Example: a hydrocarbon has an empirical formula of CH and molar mass of about 78 g/mol. The empirical mass is 13, so n = 6 and the molecular formula is C6H6, benzene. Likewise, hydrogen peroxide has an empirical formula of HO but a molecular formula of H2O2.
These ideas help chemists identify new compounds from combustion analysis in the lab. A misconception is that the empirical and molecular formulas must differ; for water they are the same. Also, forgetting to multiply every subscript, not just one, is a frequent error.
Key ideas
- n = molar mass ÷ empirical mass
- Subscripts multiply
- Needs molar mass
Quick check
Use cases: where Molecular Formula from Empirical helps
- Homework: review the key idea behind Molecular Formula from Empirical before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Molecular Formula from Empirical without notes.
- Visual learning: play with the interactive lab to see how Molecular Formula from Empirical changes when you adjust its inputs.
- Teaching a friend: explain Molecular Formula from Empirical in your own words, then compare your version with the key ideas.
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Frequently asked questions
What is Molecular Formula from Empirical?
Multiply the empirical formula by a whole number.
What will I learn in Molecular Formula from Empirical?
n = molar mass ÷ empirical mass. Subscripts multiply. Needs molar mass.
Is Molecular Formula from Empirical part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Molecular Formula from Empirical lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Molecular Formula from Empirical?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
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