What is the percent by mass of C2H3O2

Answer 1

The molar mass of each piece is:

C: 2 x 12.011 = 24.022 g/mol

H: 3 x 1.008 = 3.024 g/mol

O: 2 x 15.999 = 31.998 g/mol

The total molar mass = 24.022 + 3.024 + 31.998 = 59.044 g/mol

The percent composition by mass of carbon is the mass of carbon/total mass x 100 = 24.022/59.044 x100 = 40.7%

The percent composition by mass of hydrogen is the mass of hydrogen/total mass x 100 = 3.024/59.044 x100 = 5.1%

The percent composition by mass of oxygen is the mass of oxygen/total mass x 100 = 31.998/59.044 x100 = 54.2%

As a double check, you can add all of the percentages together to make sure you get 100% and, low and behold, 40.7% + 5.1% + 54.2% = 100%