element counts of soda ash

soda ash | elemental composition

Find the elemental composition for soda ash 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: Na_2CO_3 Use the chemical formula, Na_2CO_3, to count the number of atoms, N_i, for each element and find the total number of atoms, N_atoms: | number of atoms C (carbon) | 1 Na (sodium) | 2 O (oxygen) | 3 N_atoms = 1 + 2 + 3 = 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 C (carbon) | 1 | 1/6 Na (sodium) | 2 | 2/6 O (oxygen) | 3 | 3/6 Check: 1/6 + 2/6 + 3/6 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 1 | 1/6 × 100% = 16.7% Na (sodium) | 2 | 2/6 × 100% = 33.3% O (oxygen) | 3 | 3/6 × 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 C (carbon) | 1 | 16.7% | 12.011 Na (sodium) | 2 | 33.3% | 22.98976928 O (oxygen) | 3 | 50.0% | 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 C (carbon) | 1 | 16.7% | 12.011 | 1 × 12.011 = 12.011 Na (sodium) | 2 | 33.3% | 22.98976928 | 2 × 22.98976928 = 45.97953856 O (oxygen) | 3 | 50.0% | 15.999 | 3 × 15.999 = 47.997 m = 12.011 u + 45.97953856 u + 47.997 u = 105.98753856 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 C (carbon) | 1 | 16.7% | 12.011/105.98753856 Na (sodium) | 2 | 33.3% | 45.97953856/105.98753856 O (oxygen) | 3 | 50.0% | 47.997/105.98753856 Check: 12.011/105.98753856 + 45.97953856/105.98753856 + 47.997/105.98753856 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 1 | 16.7% | 12.011/105.98753856 × 100% = 11.33% Na (sodium) | 2 | 33.3% | 45.97953856/105.98753856 × 100% = 43.38% O (oxygen) | 3 | 50.0% | 47.997/105.98753856 × 100% = 45.29%

Mass fraction pie chart