mass fractions of sodium amminepentacyanoferrate(II)

sodium amminepentacyanoferrate(II) | elemental composition

Find the elemental composition for sodium amminepentacyanoferrate(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: Na_3[Fe(CN)_5NH_3]·xH_2O Use the chemical formula, Na_3[Fe(CN)_5NH_3]·xH_2O, 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) | 5 Fe (iron) | 1 H (hydrogen) | 5 N (nitrogen) | 6 Na (sodium) | 2 O (oxygen) | 1 N_atoms = 5 + 1 + 5 + 6 + 2 + 1 = 20 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) | 5 | 5/20 Fe (iron) | 1 | 1/20 H (hydrogen) | 5 | 5/20 N (nitrogen) | 6 | 6/20 Na (sodium) | 2 | 2/20 O (oxygen) | 1 | 1/20 Check: 5/20 + 1/20 + 5/20 + 6/20 + 2/20 + 1/20 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 5 | 5/20 × 100% = 25.0% Fe (iron) | 1 | 1/20 × 100% = 5.00% H (hydrogen) | 5 | 5/20 × 100% = 25.0% N (nitrogen) | 6 | 6/20 × 100% = 30.0% Na (sodium) | 2 | 2/20 × 100% = 10.00% O (oxygen) | 1 | 1/20 × 100% = 5.00% 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) | 5 | 25.0% | 12.011 Fe (iron) | 1 | 5.00% | 55.845 H (hydrogen) | 5 | 25.0% | 1.008 N (nitrogen) | 6 | 30.0% | 14.007 Na (sodium) | 2 | 10.00% | 22.98976928 O (oxygen) | 1 | 5.00% | 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) | 5 | 25.0% | 12.011 | 5 × 12.011 = 60.055 Fe (iron) | 1 | 5.00% | 55.845 | 1 × 55.845 = 55.845 H (hydrogen) | 5 | 25.0% | 1.008 | 5 × 1.008 = 5.040 N (nitrogen) | 6 | 30.0% | 14.007 | 6 × 14.007 = 84.042 Na (sodium) | 2 | 10.00% | 22.98976928 | 2 × 22.98976928 = 45.97953856 O (oxygen) | 1 | 5.00% | 15.999 | 1 × 15.999 = 15.999 m = 60.055 u + 55.845 u + 5.040 u + 84.042 u + 45.97953856 u + 15.999 u = 266.96053856 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) | 5 | 25.0% | 60.055/266.96053856 Fe (iron) | 1 | 5.00% | 55.845/266.96053856 H (hydrogen) | 5 | 25.0% | 5.040/266.96053856 N (nitrogen) | 6 | 30.0% | 84.042/266.96053856 Na (sodium) | 2 | 10.00% | 45.97953856/266.96053856 O (oxygen) | 1 | 5.00% | 15.999/266.96053856 Check: 60.055/266.96053856 + 55.845/266.96053856 + 5.040/266.96053856 + 84.042/266.96053856 + 45.97953856/266.96053856 + 15.999/266.96053856 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 5 | 25.0% | 60.055/266.96053856 × 100% = 22.50% Fe (iron) | 1 | 5.00% | 55.845/266.96053856 × 100% = 20.92% H (hydrogen) | 5 | 25.0% | 5.040/266.96053856 × 100% = 1.888% N (nitrogen) | 6 | 30.0% | 84.042/266.96053856 × 100% = 31.48% Na (sodium) | 2 | 10.00% | 45.97953856/266.96053856 × 100% = 17.22% O (oxygen) | 1 | 5.00% | 15.999/266.96053856 × 100% = 5.993%

Mass fraction pie chart