mass fractions of chlorine perchlorate

chlorine perchlorate | elemental composition

Find the elemental composition for chlorine perchlorate 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: Cl_2O_4 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 Cl (chlorine) | 2 O (oxygen) | 4 N_atoms = 2 + 4 = 6 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 Cl (chlorine) | 2 | 2/6 O (oxygen) | 4 | 4/6 Check: 2/6 + 4/6 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent Cl (chlorine) | 2 | 2/6 × 100% = 33.3% O (oxygen) | 4 | 4/6 × 100% = 66.7% 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 Cl (chlorine) | 2 | 33.3% | 35.45 O (oxygen) | 4 | 66.7% | 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 Cl (chlorine) | 2 | 33.3% | 35.45 | 2 × 35.45 = 70.90 O (oxygen) | 4 | 66.7% | 15.999 | 4 × 15.999 = 63.996 m = 70.90 u + 63.996 u = 134.896 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 Cl (chlorine) | 2 | 33.3% | 70.90/134.896 O (oxygen) | 4 | 66.7% | 63.996/134.896 Check: 70.90/134.896 + 63.996/134.896 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent Cl (chlorine) | 2 | 33.3% | 70.90/134.896 × 100% = 52.56% O (oxygen) | 4 | 66.7% | 63.996/134.896 × 100% = 47.44%

Mass fraction pie chart