element mass fraction of ascorbic acid

ascorbic acid | elemental composition

Find the elemental composition for ascorbic acid 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: H_2C_6H_6O_6 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) | 6 H (hydrogen) | 8 O (oxygen) | 6 N_atoms = 6 + 8 + 6 = 20 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) | 6 | 6/20 H (hydrogen) | 8 | 8/20 O (oxygen) | 6 | 6/20 Check: 6/20 + 8/20 + 6/20 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 6 | 6/20 × 100% = 30.0% H (hydrogen) | 8 | 8/20 × 100% = 40.0% O (oxygen) | 6 | 6/20 × 100% = 30.0% 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) | 6 | 30.0% | 12.011 H (hydrogen) | 8 | 40.0% | 1.008 O (oxygen) | 6 | 30.0% | 15.999 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) | 6 | 30.0% | 12.011 | 6 × 12.011 = 72.066 H (hydrogen) | 8 | 40.0% | 1.008 | 8 × 1.008 = 8.064 O (oxygen) | 6 | 30.0% | 15.999 | 6 × 15.999 = 95.994 m = 72.066 u + 8.064 u + 95.994 u = 176.124 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) | 6 | 30.0% | 72.066/176.124 H (hydrogen) | 8 | 40.0% | 8.064/176.124 O (oxygen) | 6 | 30.0% | 95.994/176.124 Check: 72.066/176.124 + 8.064/176.124 + 95.994/176.124 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 6 | 30.0% | 72.066/176.124 × 100% = 40.92% H (hydrogen) | 8 | 40.0% | 8.064/176.124 × 100% = 4.579% O (oxygen) | 6 | 30.0% | 95.994/176.124 × 100% = 54.50%

Mass fraction pie chart