Empirical Formula of Organic Compounds

salutations drowsy readers!

BE AWAKE AS ARSENIC BASED LIFE FORMS EXIST! wait.

Before we begin what the title implies, what must brush up on our limited knowledge of what we call organic compounds!

(because embedding is disabled, i must give a link)

if the point was vague,organic compounds are basically anything that contains carbon

AND TO BEGIN NOW OUR LESSON!

We can find the empirical formula of an organic compound by BURNING it. When we BURN the organic compound (reacting with oxygen), this leaves us with the BURNT(okay i'll stop) product. From the mass of the products, the moles of each element in the original UNBURNT(last one, i swear!) reactants can be calculated. 

we can do this because of the wonderful law of conservation of mass!
-the law states that the mass of the product is the same as the mass of the reactants-
it is also assumed that all carbon and all oxygen are used up during the combustion.

Sounds confusing? PERHAPS! Let us try an example!

A 10g sample is burned, producing 20g of CO2 and 8.0g of H2O. What is the empirical formula?

• convert the grams into moles
• Mol CO2 = 20g x 1mol CO2 / 44.0g CO2 = 0.455 mol CO2
• Mol H2O = 8g x 1mol H2O / 18.0g H2O = 0.444 mol H2O

• find how many moles of C and H, these are the elements that make up the organic compound
• Mol C = (0.455 mol CO2 x 1 mol C) / 1 mol CO2 = 0.455 mol C
• Mol H = (0.444 mol H2O x 2 mol H) / 1 mol H2O = 0.888 mol H

• find the empirical mass
• divide both moles by the smallest molar amount
• C = 0.455 / 0.455= 1
• H = 0.888 / 0.455 = 2

• SUM IT ALL UP!
• the empirical formula is CH2

• don't forget to check your answer!
• convert from moles to grams, it should add up to 10g
• IF your answer does not add up, remember that oxygen could be a component of the compound
• mass of O = mass of compound - mass of c + mass of H

and as this concludes the BURNT lesson, worry not readers with a BURNING passion to learn, as I leave you a feeling of toasty(wait, what?) security!

-JY