mass fractions of lead(IV) acetate

lead(IV) acetate | elemental composition

Find the elemental composition for lead(IV) acetate 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: Pb(CH_3CO_2)_4 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) | 8 H (hydrogen) | 12 O (oxygen) | 8 Pb (lead) | 1 N_atoms = 8 + 12 + 8 + 1 = 29 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) | 8 | 8/29 H (hydrogen) | 12 | 12/29 O (oxygen) | 8 | 8/29 Pb (lead) | 1 | 1/29 Check: 8/29 + 12/29 + 8/29 + 1/29 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 8 | 8/29 × 100% = 27.6% H (hydrogen) | 12 | 12/29 × 100% = 41.4% O (oxygen) | 8 | 8/29 × 100% = 27.6% Pb (lead) | 1 | 1/29 × 100% = 3.45% 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) | 8 | 27.6% | 12.011 H (hydrogen) | 12 | 41.4% | 1.008 O (oxygen) | 8 | 27.6% | 15.999 Pb (lead) | 1 | 3.45% | 207.2 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) | 8 | 27.6% | 12.011 | 8 × 12.011 = 96.088 H (hydrogen) | 12 | 41.4% | 1.008 | 12 × 1.008 = 12.096 O (oxygen) | 8 | 27.6% | 15.999 | 8 × 15.999 = 127.992 Pb (lead) | 1 | 3.45% | 207.2 | 1 × 207.2 = 207.2 m = 96.088 u + 12.096 u + 127.992 u + 207.2 u = 443.376 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) | 8 | 27.6% | 96.088/443.376 H (hydrogen) | 12 | 41.4% | 12.096/443.376 O (oxygen) | 8 | 27.6% | 127.992/443.376 Pb (lead) | 1 | 3.45% | 207.2/443.376 Check: 96.088/443.376 + 12.096/443.376 + 127.992/443.376 + 207.2/443.376 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 8 | 27.6% | 96.088/443.376 × 100% = 21.67% H (hydrogen) | 12 | 41.4% | 12.096/443.376 × 100% = 2.728% O (oxygen) | 8 | 27.6% | 127.992/443.376 × 100% = 28.87% Pb (lead) | 1 | 3.45% | 207.2/443.376 × 100% = 46.73%

Mass fraction pie chart