mass fractions of 1,3-diisopropenylbenzene

1, 3-diisopropenylbenzene | elemental composition

Find the elemental composition for 1, 3-diisopropenylbenzene 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_6H_4[C(CH_3)=CH_2]_2 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) | 12 H (hydrogen) | 14 N_atoms = 12 + 14 = 26 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) | 12 | 12/26 H (hydrogen) | 14 | 14/26 Check: 12/26 + 14/26 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 12 | 12/26 × 100% = 46.2% H (hydrogen) | 14 | 14/26 × 100% = 53.8% 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) | 12 | 46.2% | 12.011 H (hydrogen) | 14 | 53.8% | 1.008 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) | 12 | 46.2% | 12.011 | 12 × 12.011 = 144.132 H (hydrogen) | 14 | 53.8% | 1.008 | 14 × 1.008 = 14.112 m = 144.132 u + 14.112 u = 158.244 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) | 12 | 46.2% | 144.132/158.244 H (hydrogen) | 14 | 53.8% | 14.112/158.244 Check: 144.132/158.244 + 14.112/158.244 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 12 | 46.2% | 144.132/158.244 × 100% = 91.08% H (hydrogen) | 14 | 53.8% | 14.112/158.244 × 100% = 8.918%

Mass fraction pie chart