mass fractions of ruthenium(III) iodide

ruthenium(III) iodide | elemental composition

Find the elemental composition for ruthenium(III) iodide 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: RuI_3 Use the chemical formula, RuI_3, to count the number of atoms, N_i, for each element and find the total number of atoms, N_atoms: | number of atoms I (iodine) | 3 Ru (ruthenium) | 1 N_atoms = 3 + 1 = 4 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 I (iodine) | 3 | 3/4 Ru (ruthenium) | 1 | 1/4 Check: 3/4 + 1/4 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent I (iodine) | 3 | 3/4 × 100% = 75.0% Ru (ruthenium) | 1 | 1/4 × 100% = 25.0% 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 I (iodine) | 3 | 75.0% | 126.90447 Ru (ruthenium) | 1 | 25.0% | 101.07 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 I (iodine) | 3 | 75.0% | 126.90447 | 3 × 126.90447 = 380.71341 Ru (ruthenium) | 1 | 25.0% | 101.07 | 1 × 101.07 = 101.07 m = 380.71341 u + 101.07 u = 481.78341 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 I (iodine) | 3 | 75.0% | 380.71341/481.78341 Ru (ruthenium) | 1 | 25.0% | 101.07/481.78341 Check: 380.71341/481.78341 + 101.07/481.78341 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent I (iodine) | 3 | 75.0% | 380.71341/481.78341 × 100% = 79.02% Ru (ruthenium) | 1 | 25.0% | 101.07/481.78341 × 100% = 20.98%

Mass fraction pie chart