element mass fraction of acetic acid

acetic acid | elemental composition

Find the elemental composition for acetic acid in terms of the atom and mass percents: atom percent = N_i/N_atoms × 100% mass percent = (N_im_i)/m × 100% Plan: • Write the chemical formula and gather atomic masses from the periodic table. • Determine values for N_i, m_i, N_atoms and m using these items. • Finally, compute the percents and check the results. Write the chemical formula: CH_3CO_2H Use the chemical formula to count the number of atoms, N_i, for each element and find the total number of atoms, N_atoms, per molecule: | number of atoms C (carbon) | 2 H (hydrogen) | 4 O (oxygen) | 2 N_atoms = 2 + 4 + 2 = 8 Divide each N_i by N_atoms to calculate atom fractions. Then use the property that atom fractions must sum to one to check the work: | number of atoms | atom fraction C (carbon) | 2 | 2/8 H (hydrogen) | 4 | 4/8 O (oxygen) | 2 | 2/8 Check: 2/8 + 4/8 + 2/8 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 2 | 2/8 × 100% = 25.0% H (hydrogen) | 4 | 4/8 × 100% = 50.0% O (oxygen) | 2 | 2/8 × 100% = 25.0% Look up the atomic mass, m_i, in unified atomic mass units, u, for each element in the periodic table: | number of atoms | atom percent | atomic mass/u C (carbon) | 2 | 25.0% | 12.011 H (hydrogen) | 4 | 50.0% | 1.008 O (oxygen) | 2 | 25.0% | 15.999 Multiply N_i by m_i to compute the mass for each element. Then sum those values to compute the molecular mass, m: | number of atoms | atom percent | atomic mass/u | mass/u C (carbon) | 2 | 25.0% | 12.011 | 2 × 12.011 = 24.022 H (hydrogen) | 4 | 50.0% | 1.008 | 4 × 1.008 = 4.032 O (oxygen) | 2 | 25.0% | 15.999 | 2 × 15.999 = 31.998 m = 24.022 u + 4.032 u + 31.998 u = 60.052 u Divide the mass for each element by m to calculate mass fractions. Then use the property that mass fractions must sum to one to check the work: | number of atoms | atom percent | mass fraction C (carbon) | 2 | 25.0% | 24.022/60.052 H (hydrogen) | 4 | 50.0% | 4.032/60.052 O (oxygen) | 2 | 25.0% | 31.998/60.052 Check: 24.022/60.052 + 4.032/60.052 + 31.998/60.052 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 2 | 25.0% | 24.022/60.052 × 100% = 40.00% H (hydrogen) | 4 | 50.0% | 4.032/60.052 × 100% = 6.714% O (oxygen) | 2 | 25.0% | 31.998/60.052 × 100% = 53.28%

Mass fraction pie chart