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Questions 2.8

  1. What is the property of the mixture that makes fractional distillation possible? --
  2. What are the boiling points of water and ethanol? Water -------- Ethanol ------
  3. How can we know when all the more volatile component has distilled off so that we stop heating or replace the beaker receiving the distillate? -------------------
  4. What is the use of a thermometer in the distillation process? -------------------
  5. What is the use of porcelain chips at the bottom of the distillation flask? -----
  6. What is the use of fractionating column? ------------------------------------------
  7. What is the function of glass beads in the fractionating column? --------------
  8. Why is the process called fractional distillation? --------------------------------
  9. Explain the use of a Liebig condenser. -----------------------------------------------
  10. How can we test whether the distillate collected is ethanol and not water?
  11. Why is the cold water inlet of a Liebig condenser at the lower end? ---------


Answers to Questions 2.8

  1. Different yet fairly close boiling points
  2. 100oC nan 78oC respectively.
  3. When the temperature begins to rise rapidly
  4. To indicate when one component has distilled over so that we change the receiving beaker.
  5. To prevent bumping during boiling, vigorous vibrations that can break the glassware.
  6. To cool and condense back into the distillation flask, the vapour of the liquid which has not reached its boiling point, so that it does not contaminate the component that is distilling at the moment (whose boiling point has been reached).
  7. To provide a large surface area for the cooling of hot vapour so that it readily condenses.
  8. Components of a uniform liquid-liquid mixture with close but different boiling points are called a fractions (e.g. crude oil consists of fractions: diesel, petrol, diesel, kerosene and tar as its fractions).
  9. It condenses the vapour of a boiling liquid into a distillate.
  10. By holding a burning splint close to a sample of the distillate in a watch glass. Ethanol readily catches fire; but water does not.
  11. To ensure the cold running water completely fills up the jacket of the condenser before it flows out. This ensures efficient cooling