mass fractions of cupric fluoride

cupric fluoride | elemental composition

Find the elemental composition for cupric fluoride 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: CuF_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 Cu (copper) | 1 F (fluorine) | 2 N_atoms = 1 + 2 = 3 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 Cu (copper) | 1 | 1/3 F (fluorine) | 2 | 2/3 Check: 1/3 + 2/3 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent Cu (copper) | 1 | 1/3 × 100% = 33.3% F (fluorine) | 2 | 2/3 × 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 Cu (copper) | 1 | 33.3% | 63.546 F (fluorine) | 2 | 66.7% | 18.998403163 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 Cu (copper) | 1 | 33.3% | 63.546 | 1 × 63.546 = 63.546 F (fluorine) | 2 | 66.7% | 18.998403163 | 2 × 18.998403163 = 37.996806326 m = 63.546 u + 37.996806326 u = 101.542806326 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 Cu (copper) | 1 | 33.3% | 63.546/101.542806326 F (fluorine) | 2 | 66.7% | 37.996806326/101.542806326 Check: 63.546/101.542806326 + 37.996806326/101.542806326 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent Cu (copper) | 1 | 33.3% | 63.546/101.542806326 × 100% = 62.58% F (fluorine) | 2 | 66.7% | 37.996806326/101.542806326 × 100% = 37.42%

Mass fraction pie chart