mass fractions of copper phosphate

copper phosphate | elemental composition

Find the elemental composition for copper phosphate 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_3(PO_4)_2 Use the chemical formula, Cu_3(PO_4)_2, to count the number of atoms, N_i, for each element and find the total number of atoms, N_atoms: | number of atoms Cu (copper) | 1 O (oxygen) | 4 P (phosphorus) | 1 N_atoms = 1 + 4 + 1 = 6 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 Cu (copper) | 1 | 1/6 O (oxygen) | 4 | 4/6 P (phosphorus) | 1 | 1/6 Check: 1/6 + 4/6 + 1/6 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent Cu (copper) | 1 | 1/6 × 100% = 16.7% O (oxygen) | 4 | 4/6 × 100% = 66.7% P (phosphorus) | 1 | 1/6 × 100% = 16.7% 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 Cu (copper) | 1 | 16.7% | 63.546 O (oxygen) | 4 | 66.7% | 15.999 P (phosphorus) | 1 | 16.7% | 30.973761998 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 Cu (copper) | 1 | 16.7% | 63.546 | 1 × 63.546 = 63.546 O (oxygen) | 4 | 66.7% | 15.999 | 4 × 15.999 = 63.996 P (phosphorus) | 1 | 16.7% | 30.973761998 | 1 × 30.973761998 = 30.973761998 m = 63.546 u + 63.996 u + 30.973761998 u = 158.515761998 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 Cu (copper) | 1 | 16.7% | 63.546/158.515761998 O (oxygen) | 4 | 66.7% | 63.996/158.515761998 P (phosphorus) | 1 | 16.7% | 30.973761998/158.515761998 Check: 63.546/158.515761998 + 63.996/158.515761998 + 30.973761998/158.515761998 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent Cu (copper) | 1 | 16.7% | 63.546/158.515761998 × 100% = 40.09% O (oxygen) | 4 | 66.7% | 63.996/158.515761998 × 100% = 40.37% P (phosphorus) | 1 | 16.7% | 30.973761998/158.515761998 × 100% = 19.54%

Mass fraction pie chart