Input interpretation
2, 3, 7, 8, 12, 13, 17, 18-octaethyl-21H, 23 H-porphine magnesium(II) | elemental composition
Result
Find the elemental composition for 2, 3, 7, 8, 12, 13, 17, 18-octaethyl-21H, 23 H-porphine magnesium(II) 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_36H_46MgN_4)^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 Mg (magnesium) | 1 C (carbon) | 36 N (nitrogen) | 4 H (hydrogen) | 46 N_atoms = 1 + 36 + 4 + 46 = 87 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 Mg (magnesium) | 1 | 1/87 C (carbon) | 36 | 36/87 N (nitrogen) | 4 | 4/87 H (hydrogen) | 46 | 46/87 Check: 1/87 + 36/87 + 4/87 + 46/87 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent Mg (magnesium) | 1 | 1/87 × 100% = 1.15% C (carbon) | 36 | 36/87 × 100% = 41.4% N (nitrogen) | 4 | 4/87 × 100% = 4.60% H (hydrogen) | 46 | 46/87 × 100% = 52.9% 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 Mg (magnesium) | 1 | 1.15% | 24.305 C (carbon) | 36 | 41.4% | 12.011 N (nitrogen) | 4 | 4.60% | 14.007 H (hydrogen) | 46 | 52.9% | 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 Mg (magnesium) | 1 | 1.15% | 24.305 | 1 × 24.305 = 24.305 C (carbon) | 36 | 41.4% | 12.011 | 36 × 12.011 = 432.396 N (nitrogen) | 4 | 4.60% | 14.007 | 4 × 14.007 = 56.028 H (hydrogen) | 46 | 52.9% | 1.008 | 46 × 1.008 = 46.368 m = 24.305 u + 432.396 u + 56.028 u + 46.368 u = 559.097 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 Mg (magnesium) | 1 | 1.15% | 24.305/559.097 C (carbon) | 36 | 41.4% | 432.396/559.097 N (nitrogen) | 4 | 4.60% | 56.028/559.097 H (hydrogen) | 46 | 52.9% | 46.368/559.097 Check: 24.305/559.097 + 432.396/559.097 + 56.028/559.097 + 46.368/559.097 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent Mg (magnesium) | 1 | 1.15% | 24.305/559.097 × 100% = 4.347% C (carbon) | 36 | 41.4% | 432.396/559.097 × 100% = 77.34% N (nitrogen) | 4 | 4.60% | 56.028/559.097 × 100% = 10.02% H (hydrogen) | 46 | 52.9% | 46.368/559.097 × 100% = 8.293%