Empirical and Molecular Formula Mrs. Paparella December 22, 2014

Empirical Formula Simplified formula that shows the minimum ratio of elements in a compound Can be the same as the molecular formula, if the molecular formula can’t be reduced to a simplified form Examples: CH2, CH3, CH2O

Molecular Formula The true formula of a compound that shows the exact number of each element in the compound. Ex: C6H12O6 is glucose C10H14N2 is nicotine Sucrose is C12H22O11

Practice Set What is the empirical formula for the following molecular formula? C6H12O6 C10H14N2 C12H22O11 C10H22 (decane) C8H14 (octene) C5H12 (pentane) C9H8O4 (aspirin) C4H8 (butene) C27H44O (vitamin D) C6H8O6 (vitamin C)

Use the formula n=Molecular Mass Empirical Mass How to Mathematically Determine the Molecular Formula given Empirical Formula and Molecular Mass Use the formula n=Molecular Mass Empirical Mass To find the n value which is the multiplier # that states the relationship between the empirical and molecular formula To find the empirical mass you need to use the Periodic Table to look up the atomic masses of each element and figure out the total empirical mass.

Now distribute the 7 through the empirical formula Heptene has the formula mass of 98 amu, and it has the empirical formula of CH2. WhAT IS HEPTENE’S MOLECULAR FORMULA? Figure out the empirical mass using the PT. C= 1 x 12 =12 H= 1 x 2= 2 12 +2 = 14 amu (can use g/mole as well as amu) Substitute into n=Molecular Mass Empirical Mass n = 98 amu = 7 14 amu Now distribute the 7 through the empirical formula (CH2)7 = C7H14

Practice 1. Find the molecular formula of a compound with a molecular mass of 56 g/mole and an empirical formula of CH2

Answer C = 1 x 12= 12 H= 2 x 1= 2 12 +2 = 14 g/mole n= 56/14 = 4 (CH2) 4 = C4 H8