element counts of ammonium carbonate

ammonium carbonate | elemental composition

Find the elemental composition for ammonium carbonate 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: (NH_4)_2CO_3 Use the chemical formula, (NH_4)_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 H (hydrogen) | 8 N (nitrogen) | 2 O (oxygen) | 3 N_atoms = 1 + 8 + 2 + 3 = 14 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 | 1/14 H (hydrogen) | 8 | 8/14 N (nitrogen) | 2 | 2/14 O (oxygen) | 3 | 3/14 Check: 1/14 + 8/14 + 2/14 + 3/14 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 1 | 1/14 × 100% = 7.14% H (hydrogen) | 8 | 8/14 × 100% = 57.1% N (nitrogen) | 2 | 2/14 × 100% = 14.3% O (oxygen) | 3 | 3/14 × 100% = 21.4% 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 | 7.14% | 12.011 H (hydrogen) | 8 | 57.1% | 1.008 N (nitrogen) | 2 | 14.3% | 14.007 O (oxygen) | 3 | 21.4% | 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 | 7.14% | 12.011 | 1 × 12.011 = 12.011 H (hydrogen) | 8 | 57.1% | 1.008 | 8 × 1.008 = 8.064 N (nitrogen) | 2 | 14.3% | 14.007 | 2 × 14.007 = 28.014 O (oxygen) | 3 | 21.4% | 15.999 | 3 × 15.999 = 47.997 m = 12.011 u + 8.064 u + 28.014 u + 47.997 u = 96.086 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 | 7.14% | 12.011/96.086 H (hydrogen) | 8 | 57.1% | 8.064/96.086 N (nitrogen) | 2 | 14.3% | 28.014/96.086 O (oxygen) | 3 | 21.4% | 47.997/96.086 Check: 12.011/96.086 + 8.064/96.086 + 28.014/96.086 + 47.997/96.086 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 1 | 7.14% | 12.011/96.086 × 100% = 12.50% H (hydrogen) | 8 | 57.1% | 8.064/96.086 × 100% = 8.392% N (nitrogen) | 2 | 14.3% | 28.014/96.086 × 100% = 29.16% O (oxygen) | 3 | 21.4% | 47.997/96.086 × 100% = 49.95%

Mass fraction pie chart