Question

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

Answer 1

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' atomic mass. 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 atomic mass

`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...