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Empirical Formulas: Formulas in the lowest whole number ratio. Ex: NaCl MgCl2 H2O Molecular Formulas: Formulas that show the exact number of atoms of each element in a compound. Ex: C6H12O6 N2O4 H2O ** A compound can have the same EF and MF. Calculations Yeah!!!!!! Wooo-hoooo How to calculate an Ef from % comp or mass of the parts. ** If given % by mass the percents of each element are their masses in grams. Steps for calculating EF 1. Mass to moles (for each element) 2. divide by small (divide each number of moles by the smallest number of moles of all the elements in the compound.) 3. Multiply till whole. (if you get a fractional answer for one or more of the answers above. You need to multiply all the answers by whatever whole number you need to make them all whole numbers.) Example Question 11 on 10-3 R&R Worksheet How do you calculate a MF? You need 2 pieces of information. 1. You need the EF (or the info to calculate it) 2. You need the Molar Mass (GFM). Steps 1. Calculate the GFM of the EF (EF mass) 2. Divide the Molar mass by the EF mass to get whole number multiple. 3. Multiply the coefficients of the EF by the whole number multiple to get MF. Ex. #13.