mass fractions of ammonium hexabromoplatinate

ammonium hexabromoplatinate | elemental composition

Find the elemental composition for ammonium hexabromoplatinate 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: (NH_4)_2PtBr_6 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 Br (bromine) | 6 H (hydrogen) | 8 N (nitrogen) | 2 Pt (platinum) | 1 N_atoms = 6 + 8 + 2 + 1 = 17 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 Br (bromine) | 6 | 6/17 H (hydrogen) | 8 | 8/17 N (nitrogen) | 2 | 2/17 Pt (platinum) | 1 | 1/17 Check: 6/17 + 8/17 + 2/17 + 1/17 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent Br (bromine) | 6 | 6/17 × 100% = 35.3% H (hydrogen) | 8 | 8/17 × 100% = 47.1% N (nitrogen) | 2 | 2/17 × 100% = 11.8% Pt (platinum) | 1 | 1/17 × 100% = 5.88% 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 Br (bromine) | 6 | 35.3% | 79.904 H (hydrogen) | 8 | 47.1% | 1.008 N (nitrogen) | 2 | 11.8% | 14.007 Pt (platinum) | 1 | 5.88% | 195.084 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 Br (bromine) | 6 | 35.3% | 79.904 | 6 × 79.904 = 479.424 H (hydrogen) | 8 | 47.1% | 1.008 | 8 × 1.008 = 8.064 N (nitrogen) | 2 | 11.8% | 14.007 | 2 × 14.007 = 28.014 Pt (platinum) | 1 | 5.88% | 195.084 | 1 × 195.084 = 195.084 m = 479.424 u + 8.064 u + 28.014 u + 195.084 u = 710.586 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 Br (bromine) | 6 | 35.3% | 479.424/710.586 H (hydrogen) | 8 | 47.1% | 8.064/710.586 N (nitrogen) | 2 | 11.8% | 28.014/710.586 Pt (platinum) | 1 | 5.88% | 195.084/710.586 Check: 479.424/710.586 + 8.064/710.586 + 28.014/710.586 + 195.084/710.586 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent Br (bromine) | 6 | 35.3% | 479.424/710.586 × 100% = 67.47% H (hydrogen) | 8 | 47.1% | 8.064/710.586 × 100% = 1.135% N (nitrogen) | 2 | 11.8% | 28.014/710.586 × 100% = 3.942% Pt (platinum) | 1 | 5.88% | 195.084/710.586 × 100% = 27.45%

Mass fraction pie chart