element mass fraction of sodium fluoride

sodium fluoride | elemental composition

Find the elemental composition for sodium 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: NaF 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 F (fluorine) | 1 Na (sodium) | 1 N_atoms = 1 + 1 = 2 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 F (fluorine) | 1 | 1/2 Na (sodium) | 1 | 1/2 Check: 1/2 + 1/2 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent F (fluorine) | 1 | 1/2 × 100% = 50.0% Na (sodium) | 1 | 1/2 × 100% = 50.0% 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 F (fluorine) | 1 | 50.0% | 18.998403163 Na (sodium) | 1 | 50.0% | 22.98976928 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 F (fluorine) | 1 | 50.0% | 18.998403163 | 1 × 18.998403163 = 18.998403163 Na (sodium) | 1 | 50.0% | 22.98976928 | 1 × 22.98976928 = 22.98976928 m = 18.998403163 u + 22.98976928 u = 41.988172443 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 F (fluorine) | 1 | 50.0% | 18.998403163/41.988172443 Na (sodium) | 1 | 50.0% | 22.98976928/41.988172443 Check: 18.998403163/41.988172443 + 22.98976928/41.988172443 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent F (fluorine) | 1 | 50.0% | 18.998403163/41.988172443 × 100% = 45.25% Na (sodium) | 1 | 50.0% | 22.98976928/41.988172443 × 100% = 54.75%

Mass fraction pie chart