Is it possible to find a molecular formula from molar mass?
1 Answer
Not without more information.
Mass spectroscopists have computer programs that use the precise masses of isotopes and their natural abundances to calculate all the possible combinations of C, H, O, N, etc. in a molecule and then match them to a given molar mass.
We mere mortals lack such tools. We need more information like an empirical formula to find a molecular formula from the molar mass.
Example
What is the molecular formula of a compound with a molar mass of 180.16 g/mol and an empirical formula of CH₂O?
Solution
Step 1. Find the molar mass of the empirical formula.
Molar mass = (12.01 + 2×1.008 + 16.00) g/mol = 30.016 g/mol
Step 2. Find the number of empirical formula units in the molecular formula.
No. of EF units in MF =
Step 3. Find the molecular formula.
Molecular formula = (CH₂O)₆ = C₆H₁₂O₆
