element mass fraction of propane

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propane | elemental composition

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$Find the elemental composition for propane 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_2CH_3 Use the chemical formula, CH_3CH_2CH_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) | 3 H (hydrogen) | 8 N_atoms = 3 + 8 = 11 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) | 3 | 3/11 H (hydrogen) | 8 | 8/11 Check: 3/11 + 8/11 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 3 | 3/11 × 100% = 27.3% H (hydrogen) | 8 | 8/11 × 100% = 72.7% 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) | 3 | 27.3% | 12.011 H (hydrogen) | 8 | 72.7% | 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) | 3 | 27.3% | 12.011 | 3 × 12.011 = 36.033 H (hydrogen) | 8 | 72.7% | 1.008 | 8 × 1.008 = 8.064 m = 36.033 u + 8.064 u = 44.097 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) | 3 | 27.3% | 36.033/44.097 H (hydrogen) | 8 | 72.7% | 8.064/44.097 Check: 36.033/44.097 + 8.064/44.097 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 3 | 27.3% | 36.033/44.097 × 100% = 81.71% H (hydrogen) | 8 | 72.7% | 8.064/44.097 × 100% = 18.29%$

Find the elemental composition for propane 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_2CH_3 Use the chemical formula, CH_3CH_2CH_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) | 3 H (hydrogen) | 8 N_atoms = 3 + 8 = 11 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) | 3 | 3/11 H (hydrogen) | 8 | 8/11 Check: 3/11 + 8/11 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 3 | 3/11 × 100% = 27.3% H (hydrogen) | 8 | 8/11 × 100% = 72.7% 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) | 3 | 27.3% | 12.011 H (hydrogen) | 8 | 72.7% | 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) | 3 | 27.3% | 12.011 | 3 × 12.011 = 36.033 H (hydrogen) | 8 | 72.7% | 1.008 | 8 × 1.008 = 8.064 m = 36.033 u + 8.064 u = 44.097 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) | 3 | 27.3% | 36.033/44.097 H (hydrogen) | 8 | 72.7% | 8.064/44.097 Check: 36.033/44.097 + 8.064/44.097 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 3 | 27.3% | 36.033/44.097 × 100% = 81.71% H (hydrogen) | 8 | 72.7% | 8.064/44.097 × 100% = 18.29%