mass fractions of 1,2-dichlorotetrafluoroethane

1, 2-dichlorotetrafluoroethane | elemental composition

Find the elemental composition for 1, 2-dichlorotetrafluoroethane 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: ClCF_2CF_2Cl 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) | 2 Cl (chlorine) | 2 F (fluorine) | 4 N_atoms = 2 + 2 + 4 = 8 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) | 2 | 2/8 Cl (chlorine) | 2 | 2/8 F (fluorine) | 4 | 4/8 Check: 2/8 + 2/8 + 4/8 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 2 | 2/8 × 100% = 25.0% Cl (chlorine) | 2 | 2/8 × 100% = 25.0% F (fluorine) | 4 | 4/8 × 100% = 50.0% 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) | 2 | 25.0% | 12.011 Cl (chlorine) | 2 | 25.0% | 35.45 F (fluorine) | 4 | 50.0% | 18.998403163 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) | 2 | 25.0% | 12.011 | 2 × 12.011 = 24.022 Cl (chlorine) | 2 | 25.0% | 35.45 | 2 × 35.45 = 70.90 F (fluorine) | 4 | 50.0% | 18.998403163 | 4 × 18.998403163 = 75.993612652 m = 24.022 u + 70.90 u + 75.993612652 u = 170.915612652 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) | 2 | 25.0% | 24.022/170.915612652 Cl (chlorine) | 2 | 25.0% | 70.90/170.915612652 F (fluorine) | 4 | 50.0% | 75.993612652/170.915612652 Check: 24.022/170.915612652 + 70.90/170.915612652 + 75.993612652/170.915612652 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 2 | 25.0% | 24.022/170.915612652 × 100% = 14.05% Cl (chlorine) | 2 | 25.0% | 70.90/170.915612652 × 100% = 41.48% F (fluorine) | 4 | 50.0% | 75.993612652/170.915612652 × 100% = 44.46%

Mass fraction pie chart