mass fractions of 5-fluorosalicylaldehyde

5-fluorosalicylaldehyde | elemental composition

Find the elemental composition for 5-fluorosalicylaldehyde 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: FC_6H_3(OH)CHO 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) | 7 F (fluorine) | 1 H (hydrogen) | 5 O (oxygen) | 2 N_atoms = 7 + 1 + 5 + 2 = 15 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) | 7 | 7/15 F (fluorine) | 1 | 1/15 H (hydrogen) | 5 | 5/15 O (oxygen) | 2 | 2/15 Check: 7/15 + 1/15 + 5/15 + 2/15 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 7 | 7/15 × 100% = 46.7% F (fluorine) | 1 | 1/15 × 100% = 6.67% H (hydrogen) | 5 | 5/15 × 100% = 33.3% O (oxygen) | 2 | 2/15 × 100% = 13.3% 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) | 7 | 46.7% | 12.011 F (fluorine) | 1 | 6.67% | 18.998403163 H (hydrogen) | 5 | 33.3% | 1.008 O (oxygen) | 2 | 13.3% | 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) | 7 | 46.7% | 12.011 | 7 × 12.011 = 84.077 F (fluorine) | 1 | 6.67% | 18.998403163 | 1 × 18.998403163 = 18.998403163 H (hydrogen) | 5 | 33.3% | 1.008 | 5 × 1.008 = 5.040 O (oxygen) | 2 | 13.3% | 15.999 | 2 × 15.999 = 31.998 m = 84.077 u + 18.998403163 u + 5.040 u + 31.998 u = 140.113403163 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) | 7 | 46.7% | 84.077/140.113403163 F (fluorine) | 1 | 6.67% | 18.998403163/140.113403163 H (hydrogen) | 5 | 33.3% | 5.040/140.113403163 O (oxygen) | 2 | 13.3% | 31.998/140.113403163 Check: 84.077/140.113403163 + 18.998403163/140.113403163 + 5.040/140.113403163 + 31.998/140.113403163 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 7 | 46.7% | 84.077/140.113403163 × 100% = 60.01% F (fluorine) | 1 | 6.67% | 18.998403163/140.113403163 × 100% = 13.56% H (hydrogen) | 5 | 33.3% | 5.040/140.113403163 × 100% = 3.597% O (oxygen) | 2 | 13.3% | 31.998/140.113403163 × 100% = 22.84%

Mass fraction pie chart