element tally of cadmium phosphate

cadmium phosphate | elemental composition

Find the elemental composition for cadmium 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: Cd_3(PO_4)_2 Use the chemical formula, Cd_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 Cd (cadmium) | 3 O (oxygen) | 8 P (phosphorus) | 2 N_atoms = 3 + 8 + 2 = 13 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 Cd (cadmium) | 3 | 3/13 O (oxygen) | 8 | 8/13 P (phosphorus) | 2 | 2/13 Check: 3/13 + 8/13 + 2/13 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent Cd (cadmium) | 3 | 3/13 × 100% = 23.1% O (oxygen) | 8 | 8/13 × 100% = 61.5% P (phosphorus) | 2 | 2/13 × 100% = 15.4% 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 Cd (cadmium) | 3 | 23.1% | 112.414 O (oxygen) | 8 | 61.5% | 15.999 P (phosphorus) | 2 | 15.4% | 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 Cd (cadmium) | 3 | 23.1% | 112.414 | 3 × 112.414 = 337.242 O (oxygen) | 8 | 61.5% | 15.999 | 8 × 15.999 = 127.992 P (phosphorus) | 2 | 15.4% | 30.973761998 | 2 × 30.973761998 = 61.947523996 m = 337.242 u + 127.992 u + 61.947523996 u = 527.181523996 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 Cd (cadmium) | 3 | 23.1% | 337.242/527.181523996 O (oxygen) | 8 | 61.5% | 127.992/527.181523996 P (phosphorus) | 2 | 15.4% | 61.947523996/527.181523996 Check: 337.242/527.181523996 + 127.992/527.181523996 + 61.947523996/527.181523996 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent Cd (cadmium) | 3 | 23.1% | 337.242/527.181523996 × 100% = 63.97% O (oxygen) | 8 | 61.5% | 127.992/527.181523996 × 100% = 24.28% P (phosphorus) | 2 | 15.4% | 61.947523996/527.181523996 × 100% = 11.75%

Mass fraction pie chart