mass fractions of dichloromalononitrile

dichloromalononitrile | elemental composition

Find the elemental composition for dichloromalononitrile 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: NCCCl_2CN 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) | 3 Cl (chlorine) | 2 N (nitrogen) | 2 N_atoms = 3 + 2 + 2 = 7 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 | 3/7 Cl (chlorine) | 2 | 2/7 N (nitrogen) | 2 | 2/7 Check: 3/7 + 2/7 + 2/7 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 3 | 3/7 × 100% = 42.9% Cl (chlorine) | 2 | 2/7 × 100% = 28.6% N (nitrogen) | 2 | 2/7 × 100% = 28.6% 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 | 42.9% | 12.011 Cl (chlorine) | 2 | 28.6% | 35.45 N (nitrogen) | 2 | 28.6% | 14.007 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 | 42.9% | 12.011 | 3 × 12.011 = 36.033 Cl (chlorine) | 2 | 28.6% | 35.45 | 2 × 35.45 = 70.90 N (nitrogen) | 2 | 28.6% | 14.007 | 2 × 14.007 = 28.014 m = 36.033 u + 70.90 u + 28.014 u = 134.947 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 | 42.9% | 36.033/134.947 Cl (chlorine) | 2 | 28.6% | 70.90/134.947 N (nitrogen) | 2 | 28.6% | 28.014/134.947 Check: 36.033/134.947 + 70.90/134.947 + 28.014/134.947 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 3 | 42.9% | 36.033/134.947 × 100% = 26.70% Cl (chlorine) | 2 | 28.6% | 70.90/134.947 × 100% = 52.54% N (nitrogen) | 2 | 28.6% | 28.014/134.947 × 100% = 20.76%

Mass fraction pie chart