mass fractions of cyclopentane

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cyclopentane | elemental composition

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$Find the elemental composition for cyclopentane 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_5H_10 Use the chemical formula, C_5H_10, 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 N_atoms = 5 + 10 = 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) | 5 | 5/15 H (hydrogen) | 10 | 10/15 Check: 5/15 + 10/15 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 5 | 5/15 × 100% = 33.3% H (hydrogen) | 10 | 10/15 × 100% = 66.7% 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) | 5 | 33.3% | 12.011 H (hydrogen) | 10 | 66.7% | 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) | 5 | 33.3% | 12.011 | 5 × 12.011 = 60.055 H (hydrogen) | 10 | 66.7% | 1.008 | 10 × 1.008 = 10.080 m = 60.055 u + 10.080 u = 70.135 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 | 33.3% | 60.055/70.135 H (hydrogen) | 10 | 66.7% | 10.080/70.135 Check: 60.055/70.135 + 10.080/70.135 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 5 | 33.3% | 60.055/70.135 × 100% = 85.63% H (hydrogen) | 10 | 66.7% | 10.080/70.135 × 100% = 14.37%$

Find the elemental composition for cyclopentane 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_5H_10 Use the chemical formula, C_5H_10, 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 N_atoms = 5 + 10 = 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) | 5 | 5/15 H (hydrogen) | 10 | 10/15 Check: 5/15 + 10/15 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 5 | 5/15 × 100% = 33.3% H (hydrogen) | 10 | 10/15 × 100% = 66.7% 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) | 5 | 33.3% | 12.011 H (hydrogen) | 10 | 66.7% | 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) | 5 | 33.3% | 12.011 | 5 × 12.011 = 60.055 H (hydrogen) | 10 | 66.7% | 1.008 | 10 × 1.008 = 10.080 m = 60.055 u + 10.080 u = 70.135 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 | 33.3% | 60.055/70.135 H (hydrogen) | 10 | 66.7% | 10.080/70.135 Check: 60.055/70.135 + 10.080/70.135 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 5 | 33.3% | 60.055/70.135 × 100% = 85.63% H (hydrogen) | 10 | 66.7% | 10.080/70.135 × 100% = 14.37%