mass fractions of 3-(methylthio)-2-butanone

3-(methylthio)-2-butanone | elemental composition

Find the elemental composition for 3-(methylthio)-2-butanone 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_3CH(SCH_3)COCH_3 Use the chemical formula, CH_3CH(SCH_3)COCH_3, 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) | 5 H (hydrogen) | 10 O (oxygen) | 1 S (sulfur) | 1 N_atoms = 5 + 10 + 1 + 1 = 17 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) | 5 | 5/17 H (hydrogen) | 10 | 10/17 O (oxygen) | 1 | 1/17 S (sulfur) | 1 | 1/17 Check: 5/17 + 10/17 + 1/17 + 1/17 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 5 | 5/17 × 100% = 29.4% H (hydrogen) | 10 | 10/17 × 100% = 58.8% O (oxygen) | 1 | 1/17 × 100% = 5.88% S (sulfur) | 1 | 1/17 × 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) | 5 | 29.4% | 12.011 H (hydrogen) | 10 | 58.8% | 1.008 O (oxygen) | 1 | 5.88% | 15.999 S (sulfur) | 1 | 5.88% | 32.06 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) | 5 | 29.4% | 12.011 | 5 × 12.011 = 60.055 H (hydrogen) | 10 | 58.8% | 1.008 | 10 × 1.008 = 10.080 O (oxygen) | 1 | 5.88% | 15.999 | 1 × 15.999 = 15.999 S (sulfur) | 1 | 5.88% | 32.06 | 1 × 32.06 = 32.06 m = 60.055 u + 10.080 u + 15.999 u + 32.06 u = 118.194 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) | 5 | 29.4% | 60.055/118.194 H (hydrogen) | 10 | 58.8% | 10.080/118.194 O (oxygen) | 1 | 5.88% | 15.999/118.194 S (sulfur) | 1 | 5.88% | 32.06/118.194 Check: 60.055/118.194 + 10.080/118.194 + 15.999/118.194 + 32.06/118.194 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 5 | 29.4% | 60.055/118.194 × 100% = 50.81% H (hydrogen) | 10 | 58.8% | 10.080/118.194 × 100% = 8.528% O (oxygen) | 1 | 5.88% | 15.999/118.194 × 100% = 13.54% S (sulfur) | 1 | 5.88% | 32.06/118.194 × 100% = 27.12%

Mass fraction pie chart