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Questions and Answers
What is the factor that determines the physical properties of a compound?
Which type of bond is formed by the transfer of electrons?
What is the high-temperature phase of matter not commonly encountered in organic chemistry laboratories?
What occurs when the environment around a material is changed, such as by varying the temperature or pressure?
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What is the type of intermolecular force that occurs between an ion and a polar molecule?
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What is the term for the change from one state of matter to another?
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How many basic types of intermolecular forces are there?
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What is the type of intermolecular force that occurs between a polar molecule and a nonpolar molecule?
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What is the name of the forces that occur between nonpolar molecules due to electron distortion?
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What is the necessary condition for hydrogen bonding to occur?
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At what temperature does the solid phase of a compound start to change into the liquid phase at a pressure of 1 atmosphere?
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What is the definition of the melting point of a solid crystalline compound?
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What is the melting point range of a compound?
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What type of attraction is responsible for hydrogen bonding?
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What is the melting point range?
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What is one of the uses of melting point in organic chemistry?
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What is the purpose of mixed melting point?
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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?
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What happens to the sample in the capillary tube when it is turned over and tapped on the bench?
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What is the purpose of gently pressing the open end of the capillary tube into the powdered sample?
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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?
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What is the recommended height of a capillary tube sample for determining melting point?
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What is the required form of a compound before loading into a capillary tube?
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What is the purpose of attaching a capillary tube to a thermometer?
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What is the apparatus used to heat the sample gradually?
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What is the primary aim of determining the melting point of an unknown sample?
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How many experiments are typically required to determine the melting point of an unknown sample?
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What is the purpose of heating the sample gradually?
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What is the purpose of using a rubber ring to attach the capillary tube to the thermometer?
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What is the secondary purpose of determining the melting point of a compound?
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The recommended height of a capillary tube sample is 5-6 mm.
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The compound being loaded into a capillary tube must be in a liquid form.
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The Thiele apparatus is used to measure the melting point of a compound.
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The capillary tube is attached to the thermometer by a metal ring.
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The rubber ring should be below the surface of the oil bath.
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Heating is started rapidly in the melting point apparatus.
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The melting point of a compound is a physical property.
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The experiment to determine the melting point of an unknown sample requires multiple trials.
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The Digital m.p. measuring apparatus is used to measure the melting point of a compound.
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The melting point of a compound is used to determine its chemical properties.
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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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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.
