mass fractions of iron(II) carbonate

iron(II) carbonate | elemental composition

Find the elemental composition for iron(II) carbonate 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: FeCO_3 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 C (carbon) | 1 Fe (iron) | 1 O (oxygen) | 3 N_atoms = 1 + 1 + 3 = 5 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) | 1 | 1/5 Fe (iron) | 1 | 1/5 O (oxygen) | 3 | 3/5 Check: 1/5 + 1/5 + 3/5 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 1 | 1/5 × 100% = 20.0% Fe (iron) | 1 | 1/5 × 100% = 20.0% O (oxygen) | 3 | 3/5 × 100% = 60.0% 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 C (carbon) | 1 | 20.0% | 12.011 Fe (iron) | 1 | 20.0% | 55.845 O (oxygen) | 3 | 60.0% | 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) | 1 | 20.0% | 12.011 | 1 × 12.011 = 12.011 Fe (iron) | 1 | 20.0% | 55.845 | 1 × 55.845 = 55.845 O (oxygen) | 3 | 60.0% | 15.999 | 3 × 15.999 = 47.997 m = 12.011 u + 55.845 u + 47.997 u = 115.853 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) | 1 | 20.0% | 12.011/115.853 Fe (iron) | 1 | 20.0% | 55.845/115.853 O (oxygen) | 3 | 60.0% | 47.997/115.853 Check: 12.011/115.853 + 55.845/115.853 + 47.997/115.853 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 1 | 20.0% | 12.011/115.853 × 100% = 10.37% Fe (iron) | 1 | 20.0% | 55.845/115.853 × 100% = 48.20% O (oxygen) | 3 | 60.0% | 47.997/115.853 × 100% = 41.43%

Mass fraction pie chart