mass fractions of 4-prenylphlorisobutyrophenone

4-prenylphlorisobutyrophenone | elemental composition

Find the elemental composition for 4-prenylphlorisobutyrophenone 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_15H_20O_4 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) | 15 H (hydrogen) | 19 O (oxygen) | 4 N_atoms = 15 + 19 + 4 = 38 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) | 15 | 15/38 H (hydrogen) | 19 | 19/38 O (oxygen) | 4 | 4/38 Check: 15/38 + 19/38 + 4/38 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 15 | 15/38 × 100% = 39.5% H (hydrogen) | 19 | 19/38 × 100% = 50.0% O (oxygen) | 4 | 4/38 × 100% = 10.5% 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) | 15 | 39.5% | 12.011 H (hydrogen) | 19 | 50.0% | 1.008 O (oxygen) | 4 | 10.5% | 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) | 15 | 39.5% | 12.011 | 15 × 12.011 = 180.165 H (hydrogen) | 19 | 50.0% | 1.008 | 19 × 1.008 = 19.152 O (oxygen) | 4 | 10.5% | 15.999 | 4 × 15.999 = 63.996 m = 180.165 u + 19.152 u + 63.996 u = 263.313 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) | 15 | 39.5% | 180.165/263.313 H (hydrogen) | 19 | 50.0% | 19.152/263.313 O (oxygen) | 4 | 10.5% | 63.996/263.313 Check: 180.165/263.313 + 19.152/263.313 + 63.996/263.313 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 15 | 39.5% | 180.165/263.313 × 100% = 68.42% H (hydrogen) | 19 | 50.0% | 19.152/263.313 × 100% = 7.273% O (oxygen) | 4 | 10.5% | 63.996/263.313 × 100% = 24.30%

Mass fraction pie chart