Determination of Melting Point
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Questions and Answers

What is the factor that determines the physical properties of a compound?

  • Number of atoms in the molecule
  • Shape of the molecule
  • Color of the molecule
  • Type of bonds in the molecule (correct)

    • Which type of bond is formed by the transfer of electrons?

  • Covalent bond
  • Hydrogen bond
  • Dipole-dipole bond
  • Ionic bond (correct)

    • What is the high-temperature phase of matter not commonly encountered in organic chemistry laboratories?

  • Solid
  • Liquid
  • Plasma (correct)
  • Gas

    • What occurs when the environment around a material is changed, such as by varying the temperature or pressure?

    <p>A phase transition</p> Signup and view all the answers

    What is the type of intermolecular force that occurs between an ion and a polar molecule?

    <p>Ion-dipole force</p> Signup and view all the answers

    What is the term for the change from one state of matter to another?

    <p>Phase transition</p> Signup and view all the answers

    How many basic types of intermolecular forces are there?

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

    What is the type of intermolecular force that occurs between a polar molecule and a nonpolar molecule?

    <p>Dipole-induced dipole</p> Signup and view all the answers

    What is the name of the forces that occur between nonpolar molecules due to electron distortion?

    <p>London dispersion forces</p> Signup and view all the answers

    What is the necessary condition for hydrogen bonding to occur?

    <p>The presence of electronegative atoms</p> Signup and view all the answers

    At what temperature does the solid phase of a compound start to change into the liquid phase at a pressure of 1 atmosphere?

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

    What is the definition of the melting point of a solid crystalline compound?

    <p>The temperature at which the solid and liquid phases are in equilibrium at 1 atmosphere</p> Signup and view all the answers

    What is the melting point range of a compound?

    <p>The range between the temperature at which the solid starts to melt and the temperature at which it is completely melted</p> Signup and view all the answers

    What type of attraction is responsible for hydrogen bonding?

    <p>Electrostatic attraction</p> Signup and view all the answers

    What is the melting point range?

    <p>T2 - T1</p> Signup and view all the answers

    What is one of the uses of melting point in organic chemistry?

    <p>To get an indication of the purity of a compound</p> Signup and view all the answers

    What is the purpose of mixed melting point?

    <p>To determine if two samples are the same or different</p> Signup and view all the answers

    If the melting point of the mixture is less than the melting point of the original and has a wider range, what can be concluded?

    <p>The two samples are different</p> Signup and view all the answers

    What happens to the sample in the capillary tube when it is turned over and tapped on the bench?

    <p>The sample is moved to the sealed end of the tube</p> Signup and view all the answers

    What is the purpose of gently pressing the open end of the capillary tube into the powdered sample?

    <p>To fill the capillary tube with the sample</p> Signup and view all the answers

    What can be concluded if the melting point of the mixture is equal to the melting point of the original and has the same range?

    <p>The two samples are the same</p> Signup and view all the answers

    What is the recommended height of a capillary tube sample for determining melting point?

    <p>2-3 mm</p> Signup and view all the answers

    What is the required form of a compound before loading into a capillary tube?

    <p>Powdered form</p> Signup and view all the answers

    What is the purpose of attaching a capillary tube to a thermometer?

    <p>To measure the melting point of the sample</p> Signup and view all the answers

    What is the apparatus used to heat the sample gradually?

    <p>Oil bath</p> Signup and view all the answers

    What is the primary aim of determining the melting point of an unknown sample?

    <p>To identify the unknown compound</p> Signup and view all the answers

    How many experiments are typically required to determine the melting point of an unknown sample?

    <p>1</p> Signup and view all the answers

    What is the purpose of heating the sample gradually?

    <p>To ensure accurate measurement of the melting point</p> Signup and view all the answers

    What is the purpose of using a rubber ring to attach the capillary tube to the thermometer?

    <p>To ensure the capillary tube is above the surface of the oil bath</p> Signup and view all the answers

    What is the secondary purpose of determining the melting point of a compound?

    <p>To determine the purity of the compound</p> Signup and view all the answers

    The recommended height of a capillary tube sample is 5-6 mm.

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

    The compound being loaded into a capillary tube must be in a liquid form.

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

    The Thiele apparatus is used to measure the melting point of a compound.

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

    The capillary tube is attached to the thermometer by a metal ring.

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

    The rubber ring should be below the surface of the oil bath.

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

    Heating is started rapidly in the melting point apparatus.

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

    The melting point of a compound is a physical property.

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

    The experiment to determine the melting point of an unknown sample requires multiple trials.

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

    The Digital m.p. measuring apparatus is used to measure the melting point of a compound.

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

    The melting point of a compound is used to determine its chemical properties.

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

    Study Notes

    Determination of Melting Point

    • The physical properties of a compound include: Color, Odor, Refractive index, Density, Solubility, Melting point, and Boiling point.
    • Physical properties depend on molecular structure and the bonds that hold atoms together in a molecule.

    Phases of Matter

    • Matter exists in four phases: Solid, Liquid, Gas, and Plasma (high temperature phase).
    • Phase transition occurs when the environment around a material changes, such as varying temperature or pressure.

    Intermolecular Forces

    • There are four basic types of intermolecular forces:
      • Ion-dipole: Ion attracted to polar molecule.
      • Dipole-dipole: Polar molecules attracted to each other.
      • Dipole-induced dipole: Polar molecules attracted to nonpolar molecules.
      • Induced dipole-induced dipole (London dispersion forces or van der Waal's forces): Nonpolar molecules attracted to each other.

    Hydrogen Bonding

    • Hydrogen bonding is a strong type of dipole-dipole attraction.
    • A hydrogen atom serves as a bridge between two electronegative atoms.
    • For H-bonding to be important, both electronegative atoms must be from the group: F, O, N.

    Melting Point

    • The melting point of a solid crystalline compound is the temperature at which the solid and liquid phase are in equilibrium at a certain pressure (usually 1 atmosphere).
    • The melting point is the temperature at which a solid begins to change into a liquid under a pressure of 1 atmosphere.

    Melting Point Range

    • The melting point range is the range between the temperature at which the sample begins to melt (T1) and the temperature at which the sample is completely melted (T2).
    • Melting point range = T2 – T1.

    Uses of Melting Point

    • Organic chemists use the melting point to:
      • Get an indication of the purity of a compound.
      • Help in the identification of an organic compound.

    Mixed Melting Point

    • To determine if two samples are the same or different, mix them and measure the melting point of the resultant mixture.
    • If the melting point of the mixture is less than the melting point of the original and the melting point range is wider, the samples are different.
    • If the melting point of the mixture is equal to the melting point of the original and the melting point range is the same, the samples are the same.

    General Technique for Melting Point Determination

    • The capillary tube method is used to determine the melting point of a compound.
    • The sample must be in powdered form, homogeneous, and fully dried.
    • Fill the capillary tube with a sample height of 2-3 mm.
    • Attach the capillary tube to a thermometer using a rubber ring.
    • Place the tube in an oil bath and heat gradually.

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    Related Documents

    Chemistry Determination of Melting Point PDF

    Description

    Test your understanding of physical properties of organic compounds, including melting point, and how they relate to molecular structure and bonding. Learn about the importance of physical properties in chemistry and practice determining the melting point of a compound.

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