mass fractions of zinc citrate dihydrate

zinc citrate dihydrate | elemental composition

Find the elemental composition for zinc citrate dihydrate 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_6H_5O_7)_2Zn_3·2H_2O 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) | 12 H (hydrogen) | 14 O (oxygen) | 16 Zn (zinc) | 3 N_atoms = 12 + 14 + 16 + 3 = 45 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) | 12 | 12/45 H (hydrogen) | 14 | 14/45 O (oxygen) | 16 | 16/45 Zn (zinc) | 3 | 3/45 Check: 12/45 + 14/45 + 16/45 + 3/45 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 12 | 12/45 × 100% = 26.7% H (hydrogen) | 14 | 14/45 × 100% = 31.1% O (oxygen) | 16 | 16/45 × 100% = 35.6% Zn (zinc) | 3 | 3/45 × 100% = 6.67% 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) | 12 | 26.7% | 12.011 H (hydrogen) | 14 | 31.1% | 1.008 O (oxygen) | 16 | 35.6% | 15.999 Zn (zinc) | 3 | 6.67% | 65.38 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) | 12 | 26.7% | 12.011 | 12 × 12.011 = 144.132 H (hydrogen) | 14 | 31.1% | 1.008 | 14 × 1.008 = 14.112 O (oxygen) | 16 | 35.6% | 15.999 | 16 × 15.999 = 255.984 Zn (zinc) | 3 | 6.67% | 65.38 | 3 × 65.38 = 196.14 m = 144.132 u + 14.112 u + 255.984 u + 196.14 u = 610.368 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) | 12 | 26.7% | 144.132/610.368 H (hydrogen) | 14 | 31.1% | 14.112/610.368 O (oxygen) | 16 | 35.6% | 255.984/610.368 Zn (zinc) | 3 | 6.67% | 196.14/610.368 Check: 144.132/610.368 + 14.112/610.368 + 255.984/610.368 + 196.14/610.368 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 12 | 26.7% | 144.132/610.368 × 100% = 23.61% H (hydrogen) | 14 | 31.1% | 14.112/610.368 × 100% = 2.312% O (oxygen) | 16 | 35.6% | 255.984/610.368 × 100% = 41.94% Zn (zinc) | 3 | 6.67% | 196.14/610.368 × 100% = 32.13%

Mass fraction pie chart