mass fractions of (pentafluorophenyl)triethoxysilane

(pentafluorophenyl)triethoxysilane | elemental composition

Find the elemental composition for (pentafluorophenyl)triethoxysilane 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_6F_5Si(OC_2H_5)_3 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 F (fluorine) | 5 H (hydrogen) | 15 O (oxygen) | 3 Si (silicon) | 1 N_atoms = 12 + 5 + 15 + 3 + 1 = 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 F (fluorine) | 5 | 5/36 H (hydrogen) | 15 | 15/36 O (oxygen) | 3 | 3/36 Si (silicon) | 1 | 1/36 Check: 12/36 + 5/36 + 15/36 + 3/36 + 1/36 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 12 | 12/36 × 100% = 33.3% F (fluorine) | 5 | 5/36 × 100% = 13.9% H (hydrogen) | 15 | 15/36 × 100% = 41.7% O (oxygen) | 3 | 3/36 × 100% = 8.33% Si (silicon) | 1 | 1/36 × 100% = 2.78% 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 F (fluorine) | 5 | 13.9% | 18.998403163 H (hydrogen) | 15 | 41.7% | 1.008 O (oxygen) | 3 | 8.33% | 15.999 Si (silicon) | 1 | 2.78% | 28.085 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 F (fluorine) | 5 | 13.9% | 18.998403163 | 5 × 18.998403163 = 94.992015815 H (hydrogen) | 15 | 41.7% | 1.008 | 15 × 1.008 = 15.120 O (oxygen) | 3 | 8.33% | 15.999 | 3 × 15.999 = 47.997 Si (silicon) | 1 | 2.78% | 28.085 | 1 × 28.085 = 28.085 m = 144.132 u + 94.992015815 u + 15.120 u + 47.997 u + 28.085 u = 330.326015815 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% | 144.132/330.326015815 F (fluorine) | 5 | 13.9% | 94.992015815/330.326015815 H (hydrogen) | 15 | 41.7% | 15.120/330.326015815 O (oxygen) | 3 | 8.33% | 47.997/330.326015815 Si (silicon) | 1 | 2.78% | 28.085/330.326015815 Check: 144.132/330.326015815 + 94.992015815/330.326015815 + 15.120/330.326015815 + 47.997/330.326015815 + 28.085/330.326015815 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 12 | 33.3% | 144.132/330.326015815 × 100% = 43.63% F (fluorine) | 5 | 13.9% | 94.992015815/330.326015815 × 100% = 28.76% H (hydrogen) | 15 | 41.7% | 15.120/330.326015815 × 100% = 4.577% O (oxygen) | 3 | 8.33% | 47.997/330.326015815 × 100% = 14.53% Si (silicon) | 1 | 2.78% | 28.085/330.326015815 × 100% = 8.502%

Mass fraction pie chart