Question

What is the percent composition of carbon in heptane, C7H16?

Answer 1

Answer:

• Option d, 84%

Explanation:

1) Determine the molar mass of the heptane

element   # of atoms    atomic mass        total mass      

  C              7                  12.011 g/mol         7×12.011 g/mol = 84.077 g/mol

  H             16                  1.008 g/mol         16×1.008 g/mol = 16.128 g/mol

                                                                                               -------------------

                                                                   Molar mass =    100.205 g/mol

2) Percent of carbon, %

• % = (mass of element / molar mass )×100

           = (84.077 g/mol / 100.205 g/mol )×100 = 83.83 %

• Round to two significant figures: 84% ← answer