FINDING “MOLECULAR” FORMULAS… Don’t worry, this is easier than you think! Seriously you can’t do any worse at this than Bill Dance is with fishing/outdoor activities…

The Molecular Mass is the "true ratio" of the elements in a compound (ie C 6 H 12 O 6 ), whereas the empirical is the lowest whole number ratio (ie CH 2 O) FINDING “MOLECULAR” FORMULAS

Q. 1Find the molecular formula for a compound whose molar mass is 26.0g and where the % mass composition is H=7.7% and C=92.3%. Element%Mass Mass in 100g MolesMole Ratio H7.77.7g C g So the empirical formula is CH. 1. But the empirical formula is the simplified version (it has a molar mass of 12.01g+1.01g= 13.01g) but the real molar mass is 26.0g… So to find the molecular mass…

… Since the ratio of molar mass to empirical molar mass is … Then the empirical formula (CH) is multiplied by two (2) to give a Molecular formula of C 2 H 2 Molecular Formula : = # you multiply the E.F by to get the Molecular Mass!!

Q.2 Ribose is an important sugar that is found in DNA and RNA. Ribose has a molecular mass of 150g/mol, and a chemical composition of 40.0% Carbon, 6.67% Hydrogen, and 53.3% Oxygen. What is the molecular formula of Ribose? Element %Mass Mass in 100g MolesMole Ratio C40.0%40.0g H6.67%6.67g O53.3%53.3g Empirical formula is CH 2 O (molar mass = 30.0g/mol ), so…

1. Since the ratio of molar mass to empirical molar mass is 2. Then the empirical formula (CH 2 O) is multiplied by five (5) to give a Molecular formula of C 5 H 10 O 5

Let’s Try Some Practise !!! Try the back side of the Empirical Formula worksheet! A little more Bill Dance??