mass fractions of potassium oxalate monohydrate

potassium oxalate monohydrate | elemental composition

Find the elemental composition for potassium oxalate monohydrate 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: (COOK)_2·H_2O Use the chemical formula, (COOK)_2·H_2O, 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) | 2 H (hydrogen) | 2 K (potassium) | 2 O (oxygen) | 5 N_atoms = 2 + 2 + 2 + 5 = 11 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) | 2 | 2/11 H (hydrogen) | 2 | 2/11 K (potassium) | 2 | 2/11 O (oxygen) | 5 | 5/11 Check: 2/11 + 2/11 + 2/11 + 5/11 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 2 | 2/11 × 100% = 18.2% H (hydrogen) | 2 | 2/11 × 100% = 18.2% K (potassium) | 2 | 2/11 × 100% = 18.2% O (oxygen) | 5 | 5/11 × 100% = 45.5% 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) | 2 | 18.2% | 12.011 H (hydrogen) | 2 | 18.2% | 1.008 K (potassium) | 2 | 18.2% | 39.0983 O (oxygen) | 5 | 45.5% | 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) | 2 | 18.2% | 12.011 | 2 × 12.011 = 24.022 H (hydrogen) | 2 | 18.2% | 1.008 | 2 × 1.008 = 2.016 K (potassium) | 2 | 18.2% | 39.0983 | 2 × 39.0983 = 78.1966 O (oxygen) | 5 | 45.5% | 15.999 | 5 × 15.999 = 79.995 m = 24.022 u + 2.016 u + 78.1966 u + 79.995 u = 184.2296 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) | 2 | 18.2% | 24.022/184.2296 H (hydrogen) | 2 | 18.2% | 2.016/184.2296 K (potassium) | 2 | 18.2% | 78.1966/184.2296 O (oxygen) | 5 | 45.5% | 79.995/184.2296 Check: 24.022/184.2296 + 2.016/184.2296 + 78.1966/184.2296 + 79.995/184.2296 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 2 | 18.2% | 24.022/184.2296 × 100% = 13.04% H (hydrogen) | 2 | 18.2% | 2.016/184.2296 × 100% = 1.094% K (potassium) | 2 | 18.2% | 78.1966/184.2296 × 100% = 42.45% O (oxygen) | 5 | 45.5% | 79.995/184.2296 × 100% = 43.42%

Mass fraction pie chart