Question

Acetaminophen, C₈H₉NO₂, is an over-the-counter pain reliever. To three significant digits, C₈H₉NO₂ is -------------% C, -----------% H, -------------------% N, and -----------% O by mass.

Answer 1

Molar mass of C8H9NO2,

MM = 8*MM(C) + 9*MM(H) + 1*MM(N) + 2*MM(O)

= 8*12.01 + 9*1.008 + 1*14.01 + 2*16.0

= 151.162 g/mol

MM = 151.162

Lets calculate the mass of each element

mass of C = 8*MM(C)

= 96.08 g

mass of H = 9*MM(H)

= 9.072 g

mass of N = 1*MM(N)

= 14.01 g

mass of O = 2*MM(O)

= 32 g

mass % = (mass of element *100)/molar mass of compound

Now calculate mass percent of each element

Mass % of C = (96.08*100)/151.162

= 63.6 %

Mass % of H = (9.072*100)/151.162

= 6.0 %

Mass % of N = (14.01*100)/151.162

= 9.3 %

Mass % of O = (32*100)/151.162

= 21.2 %