mass fractions of 4-methoxytriphenylamine

4-methoxytriphenylamine | elemental composition

Find the elemental composition for 4-methoxytriphenylamine 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: C_19H_17NO 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) | 19 H (hydrogen) | 17 N (nitrogen) | 1 O (oxygen) | 1 N_atoms = 19 + 17 + 1 + 1 = 38 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) | 19 | 19/38 H (hydrogen) | 17 | 17/38 N (nitrogen) | 1 | 1/38 O (oxygen) | 1 | 1/38 Check: 19/38 + 17/38 + 1/38 + 1/38 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 19 | 19/38 × 100% = 50.0% H (hydrogen) | 17 | 17/38 × 100% = 44.7% N (nitrogen) | 1 | 1/38 × 100% = 2.63% O (oxygen) | 1 | 1/38 × 100% = 2.63% 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) | 19 | 50.0% | 12.011 H (hydrogen) | 17 | 44.7% | 1.008 N (nitrogen) | 1 | 2.63% | 14.007 O (oxygen) | 1 | 2.63% | 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) | 19 | 50.0% | 12.011 | 19 × 12.011 = 228.209 H (hydrogen) | 17 | 44.7% | 1.008 | 17 × 1.008 = 17.136 N (nitrogen) | 1 | 2.63% | 14.007 | 1 × 14.007 = 14.007 O (oxygen) | 1 | 2.63% | 15.999 | 1 × 15.999 = 15.999 m = 228.209 u + 17.136 u + 14.007 u + 15.999 u = 275.351 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) | 19 | 50.0% | 228.209/275.351 H (hydrogen) | 17 | 44.7% | 17.136/275.351 N (nitrogen) | 1 | 2.63% | 14.007/275.351 O (oxygen) | 1 | 2.63% | 15.999/275.351 Check: 228.209/275.351 + 17.136/275.351 + 14.007/275.351 + 15.999/275.351 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 19 | 50.0% | 228.209/275.351 × 100% = 82.88% H (hydrogen) | 17 | 44.7% | 17.136/275.351 × 100% = 6.223% N (nitrogen) | 1 | 2.63% | 14.007/275.351 × 100% = 5.087% O (oxygen) | 1 | 2.63% | 15.999/275.351 × 100% = 5.810%

Mass fraction pie chart