How can I calculate the mass percent of carbon, nitrogen and oxygen in acetamide, ##C_2H_5NO##?

The mass percent of a molecule shows the amount each element contributes to the total molecular mass.

The first step in determining the mass percent of a given molecule is to determine each of the molecule component atoms' . Since acetamine is composed of carbon, nitrogen, oxygen and hydrogen, we get

##Molar## ##mass_(carbon)## = 12.0 g/mol ##Molar## ##mass_(nitrog en)## = 14.0 g/mol ##Molar## ##mass_(o xyg en)## = 16.0 g/mol ##Molar## ##mass_(hydrog en)## = 1.00g/mol

Each element's mass contribution is determined by multiplying the number of atoms of a certain element with its molar mass

Carbon contributes ##2 * 12.0 = 24.0## g/mol;Nitrogen contributes ##1 * 14.0 = 15.0## g/mol;Oxygen contributes ##1*16.0 = 16.0## g/mol;Hydrogen contributes ##5*1.00 = 5.00## g/mol

Adding each element's contribution gives us the molecule's total

##molarmass_(C_2H_5NO) = 24.0 + 15.0 + 16.0 + 5.00=59## g/mol

The final step to determining the molecul's mass percent is to divide each elemnt's contribution by acetamide's molar mass and to multiply the result by 100%

Mass percent of Carbon = ##24.0/59.0 * 100% = 40.7%## Mass percent of Nitrogen = ##14.0/59.0 * 100% = 23.7%## Mass percent of Oxygen = ##16.0/59.0 * 100% = 27.1%## Mass percent of Hydrogen = ##5.00/59.0 = 8.50%##

Always check the validity of the answer by adding up all the percentages

##40.7 + 23.7 + 27.1 + 8.50 = 100%##

So, acetamide is 40.7% Carbon, 23.7% Nitrogen, 27.1% Oxygen, and 8.5% Hydrogen...