Take C = 12, F = 19. What is the percentage by mass of fluorine in PTFE (Teflon), whose repeat unit is –CF₂–CF₂–?
Correct answer C. 76.0%
Explanation
Molar mass of C₂F₄ = 2 × 12 + 4 × 19 = 100 g/mol. Percentage of fluorine = (76/100) × 100 = 76.0%. PTFE is made by addition polymerisation of tetrafluoroethene and is used for non-stick coatings.
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