mass fractions of iron(II) oxalate dihydrate

iron(II) oxalate dihydrate | elemental composition

Find the elemental composition for iron(II) oxalate dihydrate 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: Fe(C_2O_4)·2H_2O 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) | 2 Fe (iron) | 1 H (hydrogen) | 6 O (oxygen) | 6 N_atoms = 2 + 1 + 6 + 6 = 15 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) | 2 | 2/15 Fe (iron) | 1 | 1/15 H (hydrogen) | 6 | 6/15 O (oxygen) | 6 | 6/15 Check: 2/15 + 1/15 + 6/15 + 6/15 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 2 | 2/15 × 100% = 13.3% Fe (iron) | 1 | 1/15 × 100% = 6.67% H (hydrogen) | 6 | 6/15 × 100% = 40.0% O (oxygen) | 6 | 6/15 × 100% = 40.0% 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) | 2 | 13.3% | 12.011 Fe (iron) | 1 | 6.67% | 55.845 H (hydrogen) | 6 | 40.0% | 1.008 O (oxygen) | 6 | 40.0% | 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) | 2 | 13.3% | 12.011 | 2 × 12.011 = 24.022 Fe (iron) | 1 | 6.67% | 55.845 | 1 × 55.845 = 55.845 H (hydrogen) | 6 | 40.0% | 1.008 | 6 × 1.008 = 6.048 O (oxygen) | 6 | 40.0% | 15.999 | 6 × 15.999 = 95.994 m = 24.022 u + 55.845 u + 6.048 u + 95.994 u = 181.909 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) | 2 | 13.3% | 24.022/181.909 Fe (iron) | 1 | 6.67% | 55.845/181.909 H (hydrogen) | 6 | 40.0% | 6.048/181.909 O (oxygen) | 6 | 40.0% | 95.994/181.909 Check: 24.022/181.909 + 55.845/181.909 + 6.048/181.909 + 95.994/181.909 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 2 | 13.3% | 24.022/181.909 × 100% = 13.21% Fe (iron) | 1 | 6.67% | 55.845/181.909 × 100% = 30.70% H (hydrogen) | 6 | 40.0% | 6.048/181.909 × 100% = 3.325% O (oxygen) | 6 | 40.0% | 95.994/181.909 × 100% = 52.77%

Mass fraction pie chart