mass fractions of udp-2-acetamido-4-dehydro-2,6-dideoxyglucose

udp-2-acetamido-4-dehydro-2, 6-dideoxyglucose | elemental composition

Find the elemental composition for udp-2-acetamido-4-dehydro-2, 6-dideoxyglucose 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_17H_25N_3O_16P_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) | 17 H (hydrogen) | 25 N (nitrogen) | 3 O (oxygen) | 16 P (phosphorus) | 2 N_atoms = 17 + 25 + 3 + 16 + 2 = 63 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) | 17 | 17/63 H (hydrogen) | 25 | 25/63 N (nitrogen) | 3 | 3/63 O (oxygen) | 16 | 16/63 P (phosphorus) | 2 | 2/63 Check: 17/63 + 25/63 + 3/63 + 16/63 + 2/63 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 17 | 17/63 × 100% = 27.0% H (hydrogen) | 25 | 25/63 × 100% = 39.7% N (nitrogen) | 3 | 3/63 × 100% = 4.76% O (oxygen) | 16 | 16/63 × 100% = 25.4% P (phosphorus) | 2 | 2/63 × 100% = 3.17% 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) | 17 | 27.0% | 12.011 H (hydrogen) | 25 | 39.7% | 1.008 N (nitrogen) | 3 | 4.76% | 14.007 O (oxygen) | 16 | 25.4% | 15.999 P (phosphorus) | 2 | 3.17% | 30.973761998 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) | 17 | 27.0% | 12.011 | 17 × 12.011 = 204.187 H (hydrogen) | 25 | 39.7% | 1.008 | 25 × 1.008 = 25.200 N (nitrogen) | 3 | 4.76% | 14.007 | 3 × 14.007 = 42.021 O (oxygen) | 16 | 25.4% | 15.999 | 16 × 15.999 = 255.984 P (phosphorus) | 2 | 3.17% | 30.973761998 | 2 × 30.973761998 = 61.947523996 m = 204.187 u + 25.200 u + 42.021 u + 255.984 u + 61.947523996 u = 589.339523996 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) | 17 | 27.0% | 204.187/589.339523996 H (hydrogen) | 25 | 39.7% | 25.200/589.339523996 N (nitrogen) | 3 | 4.76% | 42.021/589.339523996 O (oxygen) | 16 | 25.4% | 255.984/589.339523996 P (phosphorus) | 2 | 3.17% | 61.947523996/589.339523996 Check: 204.187/589.339523996 + 25.200/589.339523996 + 42.021/589.339523996 + 255.984/589.339523996 + 61.947523996/589.339523996 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 17 | 27.0% | 204.187/589.339523996 × 100% = 34.65% H (hydrogen) | 25 | 39.7% | 25.200/589.339523996 × 100% = 4.276% N (nitrogen) | 3 | 4.76% | 42.021/589.339523996 × 100% = 7.130% O (oxygen) | 16 | 25.4% | 255.984/589.339523996 × 100% = 43.44% P (phosphorus) | 2 | 3.17% | 61.947523996/589.339523996 × 100% = 10.51%

Mass fraction pie chart