Organic Compounds - Formulablahblah

HAAII.

procrastinating for the win.

cats make me laugh so hard...

so last class we learned about empirical formulas, and this class we progressed to empirical formulas of ORGANIC compounds.  heres where things get tricky... :(

so a reminder: organic compounds MUST CONTAIN CARBON
-examples:  C
                    CH
                    CHO
CO is not one, because in an organic compound the hydrogen attaches to the carbon, and then the oxygen attaches to the hydrogen. NOT THE CARBON.

so to find the empirical formula of an organic compound, you need to first BURN the compound
second, you must collect and find the mass of the products (and convert to moles)

so say you have a mystery (organic) substance containing carbon and hydrogen, and when you burn it you end up with 10.0g of CO2 and 10.0g of H2O. Calculate the empirical formula.

STEPS:

1. Find the moles of the 2 compounds.

2. Divide each mole with the smallest molar mass.

3. If the resulting decimals are not even/close, multiply both substances until they are

(e.g. if you have 3.66mol H and 1 mol C, multiply both by 3 so you will have 11 mol H and 3 mol C)

4. If you are given the mass of the compound before it was burned, you should check the mass of the compound in the empirical formula to make sure it matches.  If not, then there might have been some oxygen in the original compound.

EXAMPLE

First Step: convert to moles

10.0g CO2 x 1/44 = .227mol

10.0g H20 x 1/18 = 0.556mol

Second Step: convert moles of compounds to C and H

0.227mol CO2 x 1mol C/1mol CO2 = 0.227mol C

0.556mol H2O x 2mol H/1mol H2O = 1.11mol H

and since there are 2H, then we multiply this by 2 to get a grand total of 1.11mol

Step 3: Now divide each by the smallest # of moles...

.227mol CO2 / .227 = 1

1.11mol H20 / .227 = 4.9, which rounds to 5 :)

so our empirical formula becomes CH5 

SUCCESS

Also remember to check your masses with the mass in the question (if stated) to check your answer! To do this, convert your moles of C and H back to grams and add them together. 

Total mass = grams of C + grams of H

If it's not equal (UH OH).. don't worry! There's just an extra step. Oxygen must be present, so the remainder of the grams is the grams of oxygen. Mass of O = mass of compound - mass of (C + H)

From there, convert the grams to moles and do step 3 again! Phew...

http://www.youtube.com/watch?v=9qGo9YTdnMg

^this is a video i found (and for the life of me, cant figure out how to insert...) and its kind of helpful especially if you want to isolate each element

as a reward, i has un autre chatton amusant <3

HAHAHAHAHAHAHAHAHAHAHAHAHAHAH TOOOO GOOOOOOOD

<3 Heather

Self Portrait:

sleep with one eye open...