Question

Acetaminophen (C8H9NO2) is the active ingredient in many nonprescription pain relievers. Each tablet contains 500 mg of acetaminophen, and a typical adult dose is two tablets every eight hours.
• Determine the molar mass of acetaminophen (show your work).
• Calculate the number of moles of acetaminophen in a single tablet (show your work).
• Calculate the number of moles of acetaminophen that an adult would have taken if she took three doses of acetaminophen in one day (show your work).

Answer 1

1) Molar mass C8H9NO2

Element    Atomic mass    # of atoms   mass
                       g/mol                                  g
C               12                         8               12*8 = 96
H                 1                         9                1*9 =    9
N               14                         1               14*1 = 14
O               16                        2                16*2 = 32

                              molar mass =   96 + 9 + 14 + 32 = 151 g/mol

2) Number of mols in a tablet

# of moles = mass / molar mass = 0.500 g / 151 g/mol = 0.003311 moles

3) 3 doses * 2 tablets * 0.003311 moles / tablet = 0.020 moles