mass fractions of copper 8-quinolate

copper 8-quinolate | elemental composition

Find the elemental composition for copper 8-quinolate 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_18H_12CuN_2O_2 Use the chemical formula, C_18H_12CuN_2O_2, to count the number of atoms, N_i, for each element and find the total number of atoms, N_atoms: | number of atoms C (carbon) | 18 Cu (copper) | 1 H (hydrogen) | 12 N (nitrogen) | 2 O (oxygen) | 2 N_atoms = 18 + 1 + 12 + 2 + 2 = 35 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) | 18 | 18/35 Cu (copper) | 1 | 1/35 H (hydrogen) | 12 | 12/35 N (nitrogen) | 2 | 2/35 O (oxygen) | 2 | 2/35 Check: 18/35 + 1/35 + 12/35 + 2/35 + 2/35 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 18 | 18/35 × 100% = 51.4% Cu (copper) | 1 | 1/35 × 100% = 2.86% H (hydrogen) | 12 | 12/35 × 100% = 34.3% N (nitrogen) | 2 | 2/35 × 100% = 5.71% O (oxygen) | 2 | 2/35 × 100% = 5.71% 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) | 18 | 51.4% | 12.011 Cu (copper) | 1 | 2.86% | 63.546 H (hydrogen) | 12 | 34.3% | 1.008 N (nitrogen) | 2 | 5.71% | 14.007 O (oxygen) | 2 | 5.71% | 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) | 18 | 51.4% | 12.011 | 18 × 12.011 = 216.198 Cu (copper) | 1 | 2.86% | 63.546 | 1 × 63.546 = 63.546 H (hydrogen) | 12 | 34.3% | 1.008 | 12 × 1.008 = 12.096 N (nitrogen) | 2 | 5.71% | 14.007 | 2 × 14.007 = 28.014 O (oxygen) | 2 | 5.71% | 15.999 | 2 × 15.999 = 31.998 m = 216.198 u + 63.546 u + 12.096 u + 28.014 u + 31.998 u = 351.852 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) | 18 | 51.4% | 216.198/351.852 Cu (copper) | 1 | 2.86% | 63.546/351.852 H (hydrogen) | 12 | 34.3% | 12.096/351.852 N (nitrogen) | 2 | 5.71% | 28.014/351.852 O (oxygen) | 2 | 5.71% | 31.998/351.852 Check: 216.198/351.852 + 63.546/351.852 + 12.096/351.852 + 28.014/351.852 + 31.998/351.852 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 18 | 51.4% | 216.198/351.852 × 100% = 61.45% Cu (copper) | 1 | 2.86% | 63.546/351.852 × 100% = 18.06% H (hydrogen) | 12 | 34.3% | 12.096/351.852 × 100% = 3.438% N (nitrogen) | 2 | 5.71% | 28.014/351.852 × 100% = 7.962% O (oxygen) | 2 | 5.71% | 31.998/351.852 × 100% = 9.094%

Mass fraction pie chart