mass fractions of potassium tetranitroplatinate(II)

potassium tetranitroplatinate(II) | elemental composition

Find the elemental composition for potassium tetranitroplatinate(II) 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: K_2Pt(NO_2)_4 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 K (potassium) | 2 N (nitrogen) | 4 O (oxygen) | 8 Pt (platinum) | 1 N_atoms = 2 + 4 + 8 + 1 = 15 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 K (potassium) | 2 | 2/15 N (nitrogen) | 4 | 4/15 O (oxygen) | 8 | 8/15 Pt (platinum) | 1 | 1/15 Check: 2/15 + 4/15 + 8/15 + 1/15 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent K (potassium) | 2 | 2/15 × 100% = 13.3% N (nitrogen) | 4 | 4/15 × 100% = 26.7% O (oxygen) | 8 | 8/15 × 100% = 53.3% Pt (platinum) | 1 | 1/15 × 100% = 6.67% 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 K (potassium) | 2 | 13.3% | 39.0983 N (nitrogen) | 4 | 26.7% | 14.007 O (oxygen) | 8 | 53.3% | 15.999 Pt (platinum) | 1 | 6.67% | 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 K (potassium) | 2 | 13.3% | 39.0983 | 2 × 39.0983 = 78.1966 N (nitrogen) | 4 | 26.7% | 14.007 | 4 × 14.007 = 56.028 O (oxygen) | 8 | 53.3% | 15.999 | 8 × 15.999 = 127.992 Pt (platinum) | 1 | 6.67% | 195.084 | 1 × 195.084 = 195.084 m = 78.1966 u + 56.028 u + 127.992 u + 195.084 u = 457.3006 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 K (potassium) | 2 | 13.3% | 78.1966/457.3006 N (nitrogen) | 4 | 26.7% | 56.028/457.3006 O (oxygen) | 8 | 53.3% | 127.992/457.3006 Pt (platinum) | 1 | 6.67% | 195.084/457.3006 Check: 78.1966/457.3006 + 56.028/457.3006 + 127.992/457.3006 + 195.084/457.3006 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent K (potassium) | 2 | 13.3% | 78.1966/457.3006 × 100% = 17.10% N (nitrogen) | 4 | 26.7% | 56.028/457.3006 × 100% = 12.25% O (oxygen) | 8 | 53.3% | 127.992/457.3006 × 100% = 27.99% Pt (platinum) | 1 | 6.67% | 195.084/457.3006 × 100% = 42.66%

Mass fraction pie chart