mass fractions of 2-ethylhexyl methacrylate

2-ethylhexyl methacrylate | elemental composition

Find the elemental composition for 2-ethylhexyl methacrylate 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: CH_2=C(CH_3)COOCH_2CH(C_2H_5)(CH_2)_3CH_3 Use the chemical formula, CH_2=C(CH_3)COOCH_2CH(C_2H_5)(CH_2)_3CH_3, 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) | 12 H (hydrogen) | 22 O (oxygen) | 2 N_atoms = 12 + 22 + 2 = 36 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 | 12/36 H (hydrogen) | 22 | 22/36 O (oxygen) | 2 | 2/36 Check: 12/36 + 22/36 + 2/36 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 12 | 12/36 × 100% = 33.3% H (hydrogen) | 22 | 22/36 × 100% = 61.1% O (oxygen) | 2 | 2/36 × 100% = 5.56% 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 | 33.3% | 12.011 H (hydrogen) | 22 | 61.1% | 1.008 O (oxygen) | 2 | 5.56% | 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) | 12 | 33.3% | 12.011 | 12 × 12.011 = 144.132 H (hydrogen) | 22 | 61.1% | 1.008 | 22 × 1.008 = 22.176 O (oxygen) | 2 | 5.56% | 15.999 | 2 × 15.999 = 31.998 m = 144.132 u + 22.176 u + 31.998 u = 198.306 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 | 33.3% | 144.132/198.306 H (hydrogen) | 22 | 61.1% | 22.176/198.306 O (oxygen) | 2 | 5.56% | 31.998/198.306 Check: 144.132/198.306 + 22.176/198.306 + 31.998/198.306 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 12 | 33.3% | 144.132/198.306 × 100% = 72.68% H (hydrogen) | 22 | 61.1% | 22.176/198.306 × 100% = 11.18% O (oxygen) | 2 | 5.56% | 31.998/198.306 × 100% = 16.14%

Mass fraction pie chart