mass fractions of n-methylputrescine

n-methylputrescine | elemental composition

Find the elemental composition for n-methylputrescine 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_5H_14N_2 Use the chemical formula, C_5H_14N_2, to count the number of atoms, N_i, for each element and find the total number of atoms, N_atoms: | number of atoms C (carbon) | 5 H (hydrogen) | 14 N (nitrogen) | 2 N_atoms = 5 + 14 + 2 = 21 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) | 5 | 5/21 H (hydrogen) | 14 | 14/21 N (nitrogen) | 2 | 2/21 Check: 5/21 + 14/21 + 2/21 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 5 | 5/21 × 100% = 23.8% H (hydrogen) | 14 | 14/21 × 100% = 66.7% N (nitrogen) | 2 | 2/21 × 100% = 9.52% 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) | 5 | 23.8% | 12.011 H (hydrogen) | 14 | 66.7% | 1.008 N (nitrogen) | 2 | 9.52% | 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) | 5 | 23.8% | 12.011 | 5 × 12.011 = 60.055 H (hydrogen) | 14 | 66.7% | 1.008 | 14 × 1.008 = 14.112 N (nitrogen) | 2 | 9.52% | 14.007 | 2 × 14.007 = 28.014 m = 60.055 u + 14.112 u + 28.014 u = 102.181 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) | 5 | 23.8% | 60.055/102.181 H (hydrogen) | 14 | 66.7% | 14.112/102.181 N (nitrogen) | 2 | 9.52% | 28.014/102.181 Check: 60.055/102.181 + 14.112/102.181 + 28.014/102.181 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 5 | 23.8% | 60.055/102.181 × 100% = 58.77% H (hydrogen) | 14 | 66.7% | 14.112/102.181 × 100% = 13.81% N (nitrogen) | 2 | 9.52% | 28.014/102.181 × 100% = 27.42%

Mass fraction pie chart