element counts of ethyl acetate

ethyl acetate | elemental composition

Find the elemental composition for ethyl acetate 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: CH_3COOC_2H_5 Use the chemical formula, CH_3COOC_2H_5, 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) | 4 H (hydrogen) | 8 O (oxygen) | 2 N_atoms = 4 + 8 + 2 = 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) | 4 | 4/14 H (hydrogen) | 8 | 8/14 O (oxygen) | 2 | 2/14 Check: 4/14 + 8/14 + 2/14 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 4 | 4/14 × 100% = 28.6% H (hydrogen) | 8 | 8/14 × 100% = 57.1% O (oxygen) | 2 | 2/14 × 100% = 14.3% 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) | 4 | 28.6% | 12.011 H (hydrogen) | 8 | 57.1% | 1.008 O (oxygen) | 2 | 14.3% | 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) | 4 | 28.6% | 12.011 | 4 × 12.011 = 48.044 H (hydrogen) | 8 | 57.1% | 1.008 | 8 × 1.008 = 8.064 O (oxygen) | 2 | 14.3% | 15.999 | 2 × 15.999 = 31.998 m = 48.044 u + 8.064 u + 31.998 u = 88.106 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) | 4 | 28.6% | 48.044/88.106 H (hydrogen) | 8 | 57.1% | 8.064/88.106 O (oxygen) | 2 | 14.3% | 31.998/88.106 Check: 48.044/88.106 + 8.064/88.106 + 31.998/88.106 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 4 | 28.6% | 48.044/88.106 × 100% = 54.53% H (hydrogen) | 8 | 57.1% | 8.064/88.106 × 100% = 9.153% O (oxygen) | 2 | 14.3% | 31.998/88.106 × 100% = 36.32%

Mass fraction pie chart