CHEM Assignment 18:  %Composition

1.   Penicillin, the first of a large number of antibiotics was discovered accidentally by Alexander Fleming in 1928, but he was never able to isolate it as a pure compound. Penicillin has the formula C14H20N2SO4.  Calculate is molecular weight!  Now compute the mass percent of H. %s are ("Part you're interested in / The total) x 100

Empirical and Molecular Formulas: see handout or text for help!

1.   Analysis of nicotine gave 74.0% C, 8.7% H and 17.3 % N by mass and the MW of the compound was 162 g/mole.  What is the molecular formula of nicotine?

2.   An organic compound is 92.26% C and 7.74% H.  Its molecular weight is around 80 g/mol.  Determine the empirical and the molecular formulas.

3.   Caffeine, a stimulant found in coffee, tea, and chocolate, contains 49.48% C, 5.15 % H, 28.87% N, and 16.49% O, by mass and has a MW of 194.2 g/mole.  Determine the molecular formula of caffeine.

 4.   A sample of urea, the main ingredient in urine, contains 46.7% N, 6.71% H, 20.0% C, and 26.7% O.  What is the empirical formula of urea?  If the molecular weight is around 60 g/mol what is the molecular formula?

5.   Analysis of an organic compound called ethylene glycol -properly known today as ethane diol (commonly known as "antifreeze") revealed that it contained 38.7% C, 9.7% H, and 51.6% O.  The MW is around 65 g/mol.  What are the empirical and molecular formulas?