mass fractions of dichlorofluoromethane

dichlorofluoromethane | elemental composition

Find the elemental composition for dichlorofluoromethane 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: FCHCl_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) | 1 Cl (chlorine) | 2 F (fluorine) | 1 H (hydrogen) | 1 N_atoms = 1 + 2 + 1 + 1 = 5 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) | 1 | 1/5 Cl (chlorine) | 2 | 2/5 F (fluorine) | 1 | 1/5 H (hydrogen) | 1 | 1/5 Check: 1/5 + 2/5 + 1/5 + 1/5 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 1 | 1/5 × 100% = 20.0% Cl (chlorine) | 2 | 2/5 × 100% = 40.0% F (fluorine) | 1 | 1/5 × 100% = 20.0% H (hydrogen) | 1 | 1/5 × 100% = 20.0% 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) | 1 | 20.0% | 12.011 Cl (chlorine) | 2 | 40.0% | 35.45 F (fluorine) | 1 | 20.0% | 18.998403163 H (hydrogen) | 1 | 20.0% | 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) | 1 | 20.0% | 12.011 | 1 × 12.011 = 12.011 Cl (chlorine) | 2 | 40.0% | 35.45 | 2 × 35.45 = 70.90 F (fluorine) | 1 | 20.0% | 18.998403163 | 1 × 18.998403163 = 18.998403163 H (hydrogen) | 1 | 20.0% | 1.008 | 1 × 1.008 = 1.008 m = 12.011 u + 70.90 u + 18.998403163 u + 1.008 u = 102.917403163 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) | 1 | 20.0% | 12.011/102.917403163 Cl (chlorine) | 2 | 40.0% | 70.90/102.917403163 F (fluorine) | 1 | 20.0% | 18.998403163/102.917403163 H (hydrogen) | 1 | 20.0% | 1.008/102.917403163 Check: 12.011/102.917403163 + 70.90/102.917403163 + 18.998403163/102.917403163 + 1.008/102.917403163 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 1 | 20.0% | 12.011/102.917403163 × 100% = 11.67% Cl (chlorine) | 2 | 40.0% | 70.90/102.917403163 × 100% = 68.89% F (fluorine) | 1 | 20.0% | 18.998403163/102.917403163 × 100% = 18.46% H (hydrogen) | 1 | 20.0% | 1.008/102.917403163 × 100% = 0.9794%

Mass fraction pie chart