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Dehydration of alcoholsAQA A-Level Chemistry: Flashcards

What these 13 flashcards ask

  • What type of reaction forms an alkene from an alcohol?
  • Which reagents are used to dehydrate an alcohol?
  • Write the equation for the dehydration of ethanol.
  • What is the first step in the mechanism?
  • What leaves in the second step of the mechanism?
  • What happens in the final step of the mechanism?
  • Why is the acid a catalyst in dehydration?
  • How can poly(ethene) be made without crude oil?
  • Write the equation for forming poly(ethene) from ethene.
  • Where should the thermometer bulb be in a distillation?
  • Which way does water flow through a condenser?
  • Why is the alkene product distilled off from cyclohexanol?
  • How is the percentage yield calculated?

Exam questions on Dehydration of alcohols

  1. Cyclohexanol, C₆H₁₁OH, is heated with concentrated phosphoric acid and the product is collected by distillation. Cyclohexanol boils at 161 °C and the alkene product, cyclohexene, boils at 83 °C.
    Explain why cyclohexene can be separated from the reaction mixture by distillation.2 marks
  2. A student prepares an organic liquid and wants to separate it from the reaction mixture by distillation. The mixture is placed in a round-bottomed flask with a few anti-bumping granules and heated with an electric heating mantle. The flask is joined through a still head to a condenser, and the distillate runs into a receiver flask. The student collects only the liquid that distils over between 80 °C and 85 °C.
    Explain why the student collects only the liquid that distils between 80 °C and 85 °C, and why an electric heating mantle is used rather than a Bunsen burner.2 marks
  3. A company in a country with large sugar-cane plantations but no crude oil makes ethanol by fermentation of sugar. It then converts the ethanol to ethene and makes poly(ethene) from the ethene.
    State the reagent and conditions for converting ethanol into ethene, name the type of reaction, and write the equation.3 marks
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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).