element tally of sodium phosphotungstate hydrate

sodium phosphotungstate hydrate | elemental composition

Find the elemental composition for sodium phosphotungstate hydrate 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: Na_3PO_4·12WO_3·xH_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 H (hydrogen) | 5 Na (sodium) | 3 O (oxygen) | 41 P (phosphorus) | 1 W (tungsten) | 12 N_atoms = 5 + 3 + 41 + 1 + 12 = 62 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 H (hydrogen) | 5 | 5/62 Na (sodium) | 3 | 3/62 O (oxygen) | 41 | 41/62 P (phosphorus) | 1 | 1/62 W (tungsten) | 12 | 12/62 Check: 5/62 + 3/62 + 41/62 + 1/62 + 12/62 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent H (hydrogen) | 5 | 5/62 × 100% = 8.06% Na (sodium) | 3 | 3/62 × 100% = 4.84% O (oxygen) | 41 | 41/62 × 100% = 66.1% P (phosphorus) | 1 | 1/62 × 100% = 1.61% W (tungsten) | 12 | 12/62 × 100% = 19.4% 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 H (hydrogen) | 5 | 8.06% | 1.008 Na (sodium) | 3 | 4.84% | 22.98976928 O (oxygen) | 41 | 66.1% | 15.999 P (phosphorus) | 1 | 1.61% | 30.973761998 W (tungsten) | 12 | 19.4% | 183.84 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 H (hydrogen) | 5 | 8.06% | 1.008 | 5 × 1.008 = 5.040 Na (sodium) | 3 | 4.84% | 22.98976928 | 3 × 22.98976928 = 68.96930784 O (oxygen) | 41 | 66.1% | 15.999 | 41 × 15.999 = 655.959 P (phosphorus) | 1 | 1.61% | 30.973761998 | 1 × 30.973761998 = 30.973761998 W (tungsten) | 12 | 19.4% | 183.84 | 12 × 183.84 = 2206.08 m = 5.040 u + 68.96930784 u + 655.959 u + 30.973761998 u + 2206.08 u = 2967.022069838 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 H (hydrogen) | 5 | 8.06% | 5.040/2967.022069838 Na (sodium) | 3 | 4.84% | 68.96930784/2967.022069838 O (oxygen) | 41 | 66.1% | 655.959/2967.022069838 P (phosphorus) | 1 | 1.61% | 30.973761998/2967.022069838 W (tungsten) | 12 | 19.4% | 2206.08/2967.022069838 Check: 5.040/2967.022069838 + 68.96930784/2967.022069838 + 655.959/2967.022069838 + 30.973761998/2967.022069838 + 2206.08/2967.022069838 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent H (hydrogen) | 5 | 8.06% | 5.040/2967.022069838 × 100% = 0.1699% Na (sodium) | 3 | 4.84% | 68.96930784/2967.022069838 × 100% = 2.325% O (oxygen) | 41 | 66.1% | 655.959/2967.022069838 × 100% = 22.11% P (phosphorus) | 1 | 1.61% | 30.973761998/2967.022069838 × 100% = 1.044% W (tungsten) | 12 | 19.4% | 2206.08/2967.022069838 × 100% = 74.35%

Mass fraction pie chart