Question

Polyethylene may be fluorinated by inducing the random substitution of fluorine atoms for hydrogen. For this polymer, determine the following: (a) The concentration of F (in wt percent) that must be added if this substitution occurs for 16.4 % of all of the original hydrogen atoms. (b) The concentration of F (in wt percent) that must be added to completely fluorinate the material - i.e., to produce polytetrafluoroethylene (PTFE

Answer 1

a)

Polyethylene : -(CH2-CH2)-n
For 2 Carbon there are 4 hydrogen

lets us do the calculation for 2 mol carbon only:
Number of original hydrogen = 4 mol

Number of moles of F = 16.4% of 4 = 0.164*4 = 0.656 mol
Number ofmoles of H remaining = 4 - 0.656 =3.344 mol
Number of moles of C = 2 mol

mass of F = number of moles of F* molar mass of F
                    = 0.656*19
                    = 12.464 g

Total mass of compound = 0.656*19 + 3.344*1 + 2*12 = 39.808 g

mass % of F = Mass of F*100 / total mass
                         = 12.464*100 / 39.808
                         = 31.31 %
Answer: 31.31 %

b)
2 moles of C will have 4 moles of F
mass of F = number of moles of F* molar mass of F
                    = 4*19
                    = 76 g

Total mass = 4*19 + 2*12 = 100 g

mass % of F = Mass of F*100 / total mass
                         = 76*100 / 100
                         = 76 %
Answer: 76 %