What is the mass percentage of C in penicillin, C₁₆H₁₈N₂O₄S? and What is the mass percentage of C in caffeine, C₈H₁₀N₄O₂?

Answer 1

A percent is always the part divided by the total. Therefore, find the total weight of C in the molecule and then divide by the total weight of the molecule, then multiply by 100.

To find the weight of C multiply the number of C atoms and the weight of 1 C atom (12).

12 amu x 16 = 192 amu

The weight of one penicillin molecule, we add up all the weights of the atoms

C = 12 amu x 16 = 192

H = 1 amu x 18 = 18

N = 14 amu x 2 = 28

O = 16 amu x 4 = 64

S = 32 amu x 1 = 32

Add these up...192+18+28+64+32 = 334 amu

Now divide

192/334 *100 = 57.48% C in penicillin

Do the same for caffeine.