mass fractions of bis(ethylenediamine)copper dihydroxide

bis(ethylenediamine)copper dihydroxide | elemental composition

Find the elemental composition for bis(ethylenediamine)copper dihydroxide 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: Cu(H_2NCH_2CH_2NH_2)_2(OH)_2 Use the chemical formula, Cu(H_2NCH_2CH_2NH_2)_2(OH)_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) | 2 Cu (copper) | 1 H (hydrogen) | 12 N (nitrogen) | 2 O (oxygen) | 2 N_atoms = 2 + 1 + 12 + 2 + 2 = 19 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 | 2/19 Cu (copper) | 1 | 1/19 H (hydrogen) | 12 | 12/19 N (nitrogen) | 2 | 2/19 O (oxygen) | 2 | 2/19 Check: 2/19 + 1/19 + 12/19 + 2/19 + 2/19 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 2 | 2/19 × 100% = 10.5% Cu (copper) | 1 | 1/19 × 100% = 5.26% H (hydrogen) | 12 | 12/19 × 100% = 63.2% N (nitrogen) | 2 | 2/19 × 100% = 10.5% O (oxygen) | 2 | 2/19 × 100% = 10.5% 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 | 10.5% | 12.011 Cu (copper) | 1 | 5.26% | 63.546 H (hydrogen) | 12 | 63.2% | 1.008 N (nitrogen) | 2 | 10.5% | 14.007 O (oxygen) | 2 | 10.5% | 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 | 10.5% | 12.011 | 2 × 12.011 = 24.022 Cu (copper) | 1 | 5.26% | 63.546 | 1 × 63.546 = 63.546 H (hydrogen) | 12 | 63.2% | 1.008 | 12 × 1.008 = 12.096 N (nitrogen) | 2 | 10.5% | 14.007 | 2 × 14.007 = 28.014 O (oxygen) | 2 | 10.5% | 15.999 | 2 × 15.999 = 31.998 m = 24.022 u + 63.546 u + 12.096 u + 28.014 u + 31.998 u = 159.676 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 | 10.5% | 24.022/159.676 Cu (copper) | 1 | 5.26% | 63.546/159.676 H (hydrogen) | 12 | 63.2% | 12.096/159.676 N (nitrogen) | 2 | 10.5% | 28.014/159.676 O (oxygen) | 2 | 10.5% | 31.998/159.676 Check: 24.022/159.676 + 63.546/159.676 + 12.096/159.676 + 28.014/159.676 + 31.998/159.676 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 2 | 10.5% | 24.022/159.676 × 100% = 15.04% Cu (copper) | 1 | 5.26% | 63.546/159.676 × 100% = 39.80% H (hydrogen) | 12 | 63.2% | 12.096/159.676 × 100% = 7.575% N (nitrogen) | 2 | 10.5% | 28.014/159.676 × 100% = 17.54% O (oxygen) | 2 | 10.5% | 31.998/159.676 × 100% = 20.04%

Mass fraction pie chart