mass fractions of sodium metatungstate hydrate

sodium metatungstate hydrate | elemental composition

Find the elemental composition for sodium metatungstate 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: 3Na_2WO_4·9WO_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) | 8 Na (sodium) | 6 O (oxygen) | 40 W (tungsten) | 12 N_atoms = 8 + 6 + 40 + 12 = 66 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) | 8 | 8/66 Na (sodium) | 6 | 6/66 O (oxygen) | 40 | 40/66 W (tungsten) | 12 | 12/66 Check: 8/66 + 6/66 + 40/66 + 12/66 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent H (hydrogen) | 8 | 8/66 × 100% = 12.1% Na (sodium) | 6 | 6/66 × 100% = 9.09% O (oxygen) | 40 | 40/66 × 100% = 60.6% W (tungsten) | 12 | 12/66 × 100% = 18.2% 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) | 8 | 12.1% | 1.008 Na (sodium) | 6 | 9.09% | 22.98976928 O (oxygen) | 40 | 60.6% | 15.999 W (tungsten) | 12 | 18.2% | 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) | 8 | 12.1% | 1.008 | 8 × 1.008 = 8.064 Na (sodium) | 6 | 9.09% | 22.98976928 | 6 × 22.98976928 = 137.93861568 O (oxygen) | 40 | 60.6% | 15.999 | 40 × 15.999 = 639.960 W (tungsten) | 12 | 18.2% | 183.84 | 12 × 183.84 = 2206.08 m = 8.064 u + 137.93861568 u + 639.960 u + 2206.08 u = 2992.04261568 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) | 8 | 12.1% | 8.064/2992.04261568 Na (sodium) | 6 | 9.09% | 137.93861568/2992.04261568 O (oxygen) | 40 | 60.6% | 639.960/2992.04261568 W (tungsten) | 12 | 18.2% | 2206.08/2992.04261568 Check: 8.064/2992.04261568 + 137.93861568/2992.04261568 + 639.960/2992.04261568 + 2206.08/2992.04261568 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent H (hydrogen) | 8 | 12.1% | 8.064/2992.04261568 × 100% = 0.2695% Na (sodium) | 6 | 9.09% | 137.93861568/2992.04261568 × 100% = 4.610% O (oxygen) | 40 | 60.6% | 639.960/2992.04261568 × 100% = 21.39% W (tungsten) | 12 | 18.2% | 2206.08/2992.04261568 × 100% = 73.73%

Mass fraction pie chart