Experiment: Determination of Melting Point
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Questions and Answers

What is the purpose of the experiment described in the text?

  • To measure the density of pure crystalline substances
  • To determine the boiling points of various organic compounds
  • To classify inorganic and organic compounds based on their melting points
  • To identify unknown organic compounds using their melting points (correct)

    • Why is the melting point of a pure compound considered an intensive property?

  • Because it is difficult to measure accurately
  • Because it varies with the experimental technique used
  • Because it is independent of the amount of substance present (correct)
  • Because it changes with the amount of substance present

    • Why is the determination of melting points used for identifying unknown compounds?

  • Because pure crystalline substances have a clear, sharply defined melting point (correct)
  • Because it is only applicable to inorganic compounds
  • Because it is a cost-effective technique
  • Because it is a time-consuming technique

    • What does the melting point of a compound indicate?

    <p>The purity and identity of the compound</p> Signup and view all the answers

    In what temperature range is the melting point experimentally recorded?

    <p>From the temperature at which the first crystal starts to melt until the last crystal disappears</p> Signup and view all the answers

    Why are extensive collections of tables of melting points important?

    <p>To provide exact values of many pure inorganic and organic compounds</p> Signup and view all the answers

    What is the recommended range for the sample height when loaded into a melting point capillary?

    <p>2.0 mm to 3.0 mm</p> Signup and view all the answers

    What should be done if the solid sample starts to shrink before any liquid appears during a melting-point determination?

    <p>Prepare a new sample tube and seal it</p> Signup and view all the answers

    What action should be taken if the product gives a low value even after repeating the melting point measurement more carefully with a fresh sample?

    <p>Prepare a new sample tube</p> Signup and view all the answers

    What could be a possible cause if the sample appears to melt over an excessively wide range?

    <p>Not packing the sample tightly enough</p> Signup and view all the answers

    What could be the reason for a substantially higher or lower measured melting point compared to the literature value?

    <p>The sample was heated too rapidly</p> Signup and view all the answers

    What might be the reason if the solid sample appears to shrink until there is little if any solid left at the bottom of the melting point tube?

    <p>The sample is subliming</p> Signup and view all the answers

    What should be done if small melting-point errors are suspected to result from reading the thermometer incorrectly?

    <p>Ensure correct eye level and thermometer reading position</p> Signup and view all the answers

    What should be done if the sample discolors significantly during a melting-point determination?

    <p>Assume that it's decomposing</p> Signup and view all the answers

    What is the main factor affecting the boiling point of a liquid?

    <p>Structure of the molecule and intermolecular interactions</p> Signup and view all the answers

    How does the boiling point of pure water change when a salt is added?

    <p>It increases</p> Signup and view all the answers

    What happens to the number of solvent molecules at the surface of the solution when a solute is added?

    <p>Decreases</p> Signup and view all the answers

    Why does the boiling point of pure water change when a salt is added?

    <p>Increased hydrogen bonding</p> Signup and view all the answers

    What happens to the boiling point of a liquid when its polarity increases?

    <p>Boiling point increases</p> Signup and view all the answers

    How does adding salt to water affect the boiling point?

    <p>It increases the boiling point due to increased ion-dipole interaction</p> Signup and view all the answers

    What effect does branching have on the boiling point of a liquid?

    <p>Decreases boiling point</p> Signup and view all the answers

    How do impurities affect the boiling point of a solution?

    <p>They increase the boiling point due to reduced vapor pressure</p> Signup and view all the answers

    What method can be used to determine the boiling point of a pure liquid compound?

    <p>Small-scale simple distillation apparatus</p> Signup and view all the answers

    Why do concentrated sugar-water solutions used for making candies and caramel boil at temperatures exceeding 150 °C?

    <p>Due to the dilution of water molecules</p> Signup and view all the answers

    What is the reason behind the requirement of more heat for water molecules to vaporize when salt is added to water?

    <p>Stronger ion-dipole interaction</p> Signup and view all the answers

    What effect does the addition of impurities have on the number of molecules that can vaporize at a given temperature?

    <p>It decreases the number of molecules that can vaporize</p> Signup and view all the answers

    What does the melting point apparatus assembly method help determine?

    <p>Melting point of a compound</p> Signup and view all the answers

    What is the purpose of using semi-micro scale and microscale methods for boiling point determination?

    <p>To increase accuracy in determining boiling points</p> Signup and view all the answers

    Why are extensive collections of tables of melting points important?

    <p>To provide information on melting points of compounds</p> Signup and view all the answers

    Why is the melting point of a pure compound considered an intensive property?

    <p>Because it remains constant under varying conditions</p> Signup and view all the answers

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