Calculating the Empirical Formula of a ORGANIC Compound

C_xH_2y =(burned in O₂)=> x CO₂ + y H₂O

• From the weight of CO₂ and H₂O produced by burning a definite amount of the substance, you can figure out the percent of C and H in the compound.
• Percentage of O is usually obtained by subtracting all percentages of C, H, and N, if the compound does not contain any other element.

Review Empirical Formula:

http://www.youtube.com/watch?v=HIOrWp_yLzQ

For example:

Calculate the empirical formula of a compound that is 45.99 % C, 5.38% H and the rest is O.

1. Find the moles of the compound

C:  45.99g x  1 mol / 12 g  =  3.8325 moles

H:  5.38g x 1 mol  /  1.0 g  =  5.38 moles

O:   

• 45.99 + 5.38 = 51.37
• 100 - 51.37 = 48.63  -->  O

48.63 x 1 mol  /  16 g  =  3.039375 moles

2. Divide each answer with the lowest number, which is the oxygen.

C:  3.8325 / 3.039375 = 1.260950031 -->  1.27 x 4 = 5
H:  5.38 / 3.039375 = 1.770100761-->  1.77 x 4 = 7
O:  3.03975 / 3.03975  =  1-->  1 x 4 = 4

ANS:  C₅H₇O₄

By: Hikari Hoshika