mass fractions of creatine-phosphate

creatine-phosphate | elemental composition

Find the elemental composition for creatine-phosphate 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_4H_10N_3O_5P_1 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) | 4 H (hydrogen) | 12 N (nitrogen) | 3 O (oxygen) | 6 P (phosphorus) | 1 N_atoms = 4 + 12 + 3 + 6 + 1 = 26 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) | 4 | 4/26 H (hydrogen) | 12 | 12/26 N (nitrogen) | 3 | 3/26 O (oxygen) | 6 | 6/26 P (phosphorus) | 1 | 1/26 Check: 4/26 + 12/26 + 3/26 + 6/26 + 1/26 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 4 | 4/26 × 100% = 15.4% H (hydrogen) | 12 | 12/26 × 100% = 46.2% N (nitrogen) | 3 | 3/26 × 100% = 11.5% O (oxygen) | 6 | 6/26 × 100% = 23.1% P (phosphorus) | 1 | 1/26 × 100% = 3.85% 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) | 4 | 15.4% | 12.011 H (hydrogen) | 12 | 46.2% | 1.008 N (nitrogen) | 3 | 11.5% | 14.007 O (oxygen) | 6 | 23.1% | 15.999 P (phosphorus) | 1 | 3.85% | 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) | 4 | 15.4% | 12.011 | 4 × 12.011 = 48.044 H (hydrogen) | 12 | 46.2% | 1.008 | 12 × 1.008 = 12.096 N (nitrogen) | 3 | 11.5% | 14.007 | 3 × 14.007 = 42.021 O (oxygen) | 6 | 23.1% | 15.999 | 6 × 15.999 = 95.994 P (phosphorus) | 1 | 3.85% | 30.973761998 | 1 × 30.973761998 = 30.973761998 m = 48.044 u + 12.096 u + 42.021 u + 95.994 u + 30.973761998 u = 229.128761998 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) | 4 | 15.4% | 48.044/229.128761998 H (hydrogen) | 12 | 46.2% | 12.096/229.128761998 N (nitrogen) | 3 | 11.5% | 42.021/229.128761998 O (oxygen) | 6 | 23.1% | 95.994/229.128761998 P (phosphorus) | 1 | 3.85% | 30.973761998/229.128761998 Check: 48.044/229.128761998 + 12.096/229.128761998 + 42.021/229.128761998 + 95.994/229.128761998 + 30.973761998/229.128761998 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 4 | 15.4% | 48.044/229.128761998 × 100% = 20.97% H (hydrogen) | 12 | 46.2% | 12.096/229.128761998 × 100% = 5.279% N (nitrogen) | 3 | 11.5% | 42.021/229.128761998 × 100% = 18.34% O (oxygen) | 6 | 23.1% | 95.994/229.128761998 × 100% = 41.90% P (phosphorus) | 1 | 3.85% | 30.973761998/229.128761998 × 100% = 13.52%

Mass fraction pie chart