mass fractions of thallium(I) nitrite

thallium(I) nitrite | elemental composition

Find the elemental composition for thallium(I) nitrite 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: TlNO_2 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) | 1 O (oxygen) | 2 Tl (thallium) | 1 N_atoms = 1 + 2 + 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 N (nitrogen) | 1 | 1/4 O (oxygen) | 2 | 2/4 Tl (thallium) | 1 | 1/4 Check: 1/4 + 2/4 + 1/4 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent N (nitrogen) | 1 | 1/4 × 100% = 25.0% O (oxygen) | 2 | 2/4 × 100% = 50.0% Tl (thallium) | 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 N (nitrogen) | 1 | 25.0% | 14.007 O (oxygen) | 2 | 50.0% | 15.999 Tl (thallium) | 1 | 25.0% | 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) | 1 | 25.0% | 14.007 | 1 × 14.007 = 14.007 O (oxygen) | 2 | 50.0% | 15.999 | 2 × 15.999 = 31.998 Tl (thallium) | 1 | 25.0% | 204.38 | 1 × 204.38 = 204.38 m = 14.007 u + 31.998 u + 204.38 u = 250.385 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) | 1 | 25.0% | 14.007/250.385 O (oxygen) | 2 | 50.0% | 31.998/250.385 Tl (thallium) | 1 | 25.0% | 204.38/250.385 Check: 14.007/250.385 + 31.998/250.385 + 204.38/250.385 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent N (nitrogen) | 1 | 25.0% | 14.007/250.385 × 100% = 5.594% O (oxygen) | 2 | 50.0% | 31.998/250.385 × 100% = 12.78% Tl (thallium) | 1 | 25.0% | 204.38/250.385 × 100% = 81.63%

Mass fraction pie chart