To calculate the percent composition by mass of a compound like C2H5OH, determine the masses of each element in the compound. For C2H5OH, the percent composition would be C = 52.14%, H = 13.15%, and O = 34.71%.
To calculate the present composition by mass of a compound, such as C2H5OH, we need to determine the masses of each element in the compound. In C2H5OH, there are 2 carbon (C) atoms, 6 hydrogen (H) atoms, and 1 oxygen (O) atom.
The molar mass of C2H5OH is found by adding the atomic masses of each element: (2 x atomic mass of C) + (6 x atomic mass of H) + (1 x atomic mass of O).
Once we have the molar mass, we can calculate the percentage of each element in the compound by dividing the mass of each element by the total molar mass, and then multiplying by 100%.
In this case, the percent composition by mass of C2H5OH would be: C = 52.14%, H = 13.15%, and O = 34.71%.