mass fractions of toluene

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toluene | elemental composition

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$Find the elemental composition for toluene 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_5CH_3 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 H (hydrogen) | 8 N_atoms = 7 + 8 = 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 H (hydrogen) | 8 | 8/15 Check: 7/15 + 8/15 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 7 | 7/15 × 100% = 46.7% H (hydrogen) | 8 | 8/15 × 100% = 53.3% 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 H (hydrogen) | 8 | 53.3% | 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) | 7 | 46.7% | 12.011 | 7 × 12.011 = 84.077 H (hydrogen) | 8 | 53.3% | 1.008 | 8 × 1.008 = 8.064 m = 84.077 u + 8.064 u = 92.141 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% | 84.077/92.141 H (hydrogen) | 8 | 53.3% | 8.064/92.141 Check: 84.077/92.141 + 8.064/92.141 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 7 | 46.7% | 84.077/92.141 × 100% = 91.25% H (hydrogen) | 8 | 53.3% | 8.064/92.141 × 100% = 8.752%$

Find the elemental composition for toluene 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_5CH_3 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 H (hydrogen) | 8 N_atoms = 7 + 8 = 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 H (hydrogen) | 8 | 8/15 Check: 7/15 + 8/15 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 7 | 7/15 × 100% = 46.7% H (hydrogen) | 8 | 8/15 × 100% = 53.3% 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 H (hydrogen) | 8 | 53.3% | 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) | 7 | 46.7% | 12.011 | 7 × 12.011 = 84.077 H (hydrogen) | 8 | 53.3% | 1.008 | 8 × 1.008 = 8.064 m = 84.077 u + 8.064 u = 92.141 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% | 84.077/92.141 H (hydrogen) | 8 | 53.3% | 8.064/92.141 Check: 84.077/92.141 + 8.064/92.141 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 7 | 46.7% | 84.077/92.141 × 100% = 91.25% H (hydrogen) | 8 | 53.3% | 8.064/92.141 × 100% = 8.752%