element mass fraction of (5z,9e,14z)-(8xi,11xi,12s)-8,11,12-trihydroxyicosa-5,9,14-trienoate

(5z, 9e, 14z)-(8xi, 11xi, 12s)-8, 11, 12-trihydroxyicosa-5, 9, 14-trienoate | elemental composition

Find the elemental composition for (5z, 9e, 14z)-(8xi, 11xi, 12s)-8, 11, 12-trihydroxyicosa-5, 9, 14-trienoate 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_20H_34O_5 Use the chemical formula, C_20H_34O_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) | 20 H (hydrogen) | 33 O (oxygen) | 5 N_atoms = 20 + 33 + 5 = 58 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) | 20 | 20/58 H (hydrogen) | 33 | 33/58 O (oxygen) | 5 | 5/58 Check: 20/58 + 33/58 + 5/58 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 20 | 20/58 × 100% = 34.5% H (hydrogen) | 33 | 33/58 × 100% = 56.9% O (oxygen) | 5 | 5/58 × 100% = 8.62% 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) | 20 | 34.5% | 12.011 H (hydrogen) | 33 | 56.9% | 1.008 O (oxygen) | 5 | 8.62% | 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) | 20 | 34.5% | 12.011 | 20 × 12.011 = 240.220 H (hydrogen) | 33 | 56.9% | 1.008 | 33 × 1.008 = 33.264 O (oxygen) | 5 | 8.62% | 15.999 | 5 × 15.999 = 79.995 m = 240.220 u + 33.264 u + 79.995 u = 353.479 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) | 20 | 34.5% | 240.220/353.479 H (hydrogen) | 33 | 56.9% | 33.264/353.479 O (oxygen) | 5 | 8.62% | 79.995/353.479 Check: 240.220/353.479 + 33.264/353.479 + 79.995/353.479 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 20 | 34.5% | 240.220/353.479 × 100% = 67.96% H (hydrogen) | 33 | 56.9% | 33.264/353.479 × 100% = 9.410% O (oxygen) | 5 | 8.62% | 79.995/353.479 × 100% = 22.63%

Mass fraction pie chart