mass fractions of thallium(III) nitrate

thallium(III) nitrate | elemental composition

Find the elemental composition for thallium(III) nitrate 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: N_3O_9Tl 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 N (nitrogen) | 3 O (oxygen) | 9 Tl (thallium) | 1 N_atoms = 3 + 9 + 1 = 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 N (nitrogen) | 3 | 3/13 O (oxygen) | 9 | 9/13 Tl (thallium) | 1 | 1/13 Check: 3/13 + 9/13 + 1/13 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent N (nitrogen) | 3 | 3/13 × 100% = 23.1% O (oxygen) | 9 | 9/13 × 100% = 69.2% Tl (thallium) | 1 | 1/13 × 100% = 7.69% 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 N (nitrogen) | 3 | 23.1% | 14.007 O (oxygen) | 9 | 69.2% | 15.999 Tl (thallium) | 1 | 7.69% | 204.38 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 N (nitrogen) | 3 | 23.1% | 14.007 | 3 × 14.007 = 42.021 O (oxygen) | 9 | 69.2% | 15.999 | 9 × 15.999 = 143.991 Tl (thallium) | 1 | 7.69% | 204.38 | 1 × 204.38 = 204.38 m = 42.021 u + 143.991 u + 204.38 u = 390.392 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 N (nitrogen) | 3 | 23.1% | 42.021/390.392 O (oxygen) | 9 | 69.2% | 143.991/390.392 Tl (thallium) | 1 | 7.69% | 204.38/390.392 Check: 42.021/390.392 + 143.991/390.392 + 204.38/390.392 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent N (nitrogen) | 3 | 23.1% | 42.021/390.392 × 100% = 10.76% O (oxygen) | 9 | 69.2% | 143.991/390.392 × 100% = 36.88% Tl (thallium) | 1 | 7.69% | 204.38/390.392 × 100% = 52.35%

Mass fraction pie chart