element counts of etomidate

etomidate | elemental composition

Find the elemental composition for etomidate 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: C_14H_16N_2O_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 C (carbon) | 14 H (hydrogen) | 16 N (nitrogen) | 2 O (oxygen) | 2 N_atoms = 14 + 16 + 2 + 2 = 34 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) | 14 | 14/34 H (hydrogen) | 16 | 16/34 N (nitrogen) | 2 | 2/34 O (oxygen) | 2 | 2/34 Check: 14/34 + 16/34 + 2/34 + 2/34 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 14 | 14/34 × 100% = 41.2% H (hydrogen) | 16 | 16/34 × 100% = 47.1% N (nitrogen) | 2 | 2/34 × 100% = 5.88% O (oxygen) | 2 | 2/34 × 100% = 5.88% 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) | 14 | 41.2% | 12.011 H (hydrogen) | 16 | 47.1% | 1.008 N (nitrogen) | 2 | 5.88% | 14.007 O (oxygen) | 2 | 5.88% | 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) | 14 | 41.2% | 12.011 | 14 × 12.011 = 168.154 H (hydrogen) | 16 | 47.1% | 1.008 | 16 × 1.008 = 16.128 N (nitrogen) | 2 | 5.88% | 14.007 | 2 × 14.007 = 28.014 O (oxygen) | 2 | 5.88% | 15.999 | 2 × 15.999 = 31.998 m = 168.154 u + 16.128 u + 28.014 u + 31.998 u = 244.294 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) | 14 | 41.2% | 168.154/244.294 H (hydrogen) | 16 | 47.1% | 16.128/244.294 N (nitrogen) | 2 | 5.88% | 28.014/244.294 O (oxygen) | 2 | 5.88% | 31.998/244.294 Check: 168.154/244.294 + 16.128/244.294 + 28.014/244.294 + 31.998/244.294 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 14 | 41.2% | 168.154/244.294 × 100% = 68.83% H (hydrogen) | 16 | 47.1% | 16.128/244.294 × 100% = 6.602% N (nitrogen) | 2 | 5.88% | 28.014/244.294 × 100% = 11.47% O (oxygen) | 2 | 5.88% | 31.998/244.294 × 100% = 13.10%

Mass fraction pie chart