mass fractions of calcium chlorite

calcium chlorite | elemental composition

Find the elemental composition for calcium chlorite 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: Ca(ClO_2)_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 Ca (calcium) | 1 Cl (chlorine) | 2 O (oxygen) | 4 N_atoms = 1 + 2 + 4 = 7 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 Ca (calcium) | 1 | 1/7 Cl (chlorine) | 2 | 2/7 O (oxygen) | 4 | 4/7 Check: 1/7 + 2/7 + 4/7 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent Ca (calcium) | 1 | 1/7 × 100% = 14.3% Cl (chlorine) | 2 | 2/7 × 100% = 28.6% O (oxygen) | 4 | 4/7 × 100% = 57.1% 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 Ca (calcium) | 1 | 14.3% | 40.078 Cl (chlorine) | 2 | 28.6% | 35.45 O (oxygen) | 4 | 57.1% | 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 Ca (calcium) | 1 | 14.3% | 40.078 | 1 × 40.078 = 40.078 Cl (chlorine) | 2 | 28.6% | 35.45 | 2 × 35.45 = 70.90 O (oxygen) | 4 | 57.1% | 15.999 | 4 × 15.999 = 63.996 m = 40.078 u + 70.90 u + 63.996 u = 174.974 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 Ca (calcium) | 1 | 14.3% | 40.078/174.974 Cl (chlorine) | 2 | 28.6% | 70.90/174.974 O (oxygen) | 4 | 57.1% | 63.996/174.974 Check: 40.078/174.974 + 70.90/174.974 + 63.996/174.974 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent Ca (calcium) | 1 | 14.3% | 40.078/174.974 × 100% = 22.91% Cl (chlorine) | 2 | 28.6% | 70.90/174.974 × 100% = 40.52% O (oxygen) | 4 | 57.1% | 63.996/174.974 × 100% = 36.57%

Mass fraction pie chart