mass fractions of zinc chlorate

zinc chlorate | elemental composition

Find the elemental composition for zinc chlorate 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: Zn(ClO_3)_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 Cl (chlorine) | 2 O (oxygen) | 6 Zn (zinc) | 1 N_atoms = 2 + 6 + 1 = 9 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 | 2/9 O (oxygen) | 6 | 6/9 Zn (zinc) | 1 | 1/9 Check: 2/9 + 6/9 + 1/9 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent Cl (chlorine) | 2 | 2/9 × 100% = 22.2% O (oxygen) | 6 | 6/9 × 100% = 66.7% Zn (zinc) | 1 | 1/9 × 100% = 11.1% 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 Cl (chlorine) | 2 | 22.2% | 35.45 O (oxygen) | 6 | 66.7% | 15.999 Zn (zinc) | 1 | 11.1% | 65.38 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 Cl (chlorine) | 2 | 22.2% | 35.45 | 2 × 35.45 = 70.90 O (oxygen) | 6 | 66.7% | 15.999 | 6 × 15.999 = 95.994 Zn (zinc) | 1 | 11.1% | 65.38 | 1 × 65.38 = 65.38 m = 70.90 u + 95.994 u + 65.38 u = 232.274 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 | 22.2% | 70.90/232.274 O (oxygen) | 6 | 66.7% | 95.994/232.274 Zn (zinc) | 1 | 11.1% | 65.38/232.274 Check: 70.90/232.274 + 95.994/232.274 + 65.38/232.274 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent Cl (chlorine) | 2 | 22.2% | 70.90/232.274 × 100% = 30.52% O (oxygen) | 6 | 66.7% | 95.994/232.274 × 100% = 41.33% Zn (zinc) | 1 | 11.1% | 65.38/232.274 × 100% = 28.15%

Mass fraction pie chart