Aspirin is a compound with the molecular formula C9H89O4. what is it's percentage composition?

Answer 1

Firstly, your molecular formula has a typo. Aspirin is C₉H₈O₄. Using this formula we first compute the molar mass (also called the molecular weight, or molecular mass). Using values from the periodic table:

C 9 x 12.01 g/mol = 108.09 g/mol

H 8 x 1.01 g/mol = 8.08 g/mol

O 4 x 16.00 g/mol = 64.00 g/mol

Total Mass 180.17 g/mol

To calculate % composition we take the individual total for each element and divide by the total mass.

So:

C 108.09/180.17 = .5999 = 59.99% C

H 8.08/180.17 = .04484 = 4.48 % H

O 64.00/180.17 = .3552 = 35.52% O.

Note: There is a slight error created by dropping the decimal points/rounding which causes the totals to add up to 99.99%. This goes away if you round the %C to 60.0%.