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LAB 1- ASSESSMENT OF PHYSICAL PROPERTIES OF ORGANIC COMPOUNDS

  • Page ID
    506258
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    Determination of Melting and Boiling Points of Organic Compounds

    PURPOSE

    The purpose of this experiment is to:

    • Determine the melting point of known and unknown organic solids.
    • Set up and use a simple distillation apparatus to determine the boiling point of a known and an unknown organic liquid.
    • Determine the identities of unknown substances based on their melting and boiling points.
    • Identify the functional groups present in organic compounds.

    INTRODUCTION

    In general chemistry, you learned that each compound has a unique melting and boiling point. These physical properties, along with other methods, can aid in identifying organic compounds. The melting point is the temperature at which a converted into a liquid. The melting point of an organic solid can be measured using a melting point apparatus. In this lab, you will use the Vernier melt station to experimentally find the melting point of benzoic acid and an unknown organic compound.

    The boiling point is the temperature at which a liquid is converted into a gas. The boiling points of organic liquids can be determined using simple distillation, as shown below.

    Simple distillation apparatus with most of the eqipment labeled
    Figure \(\PageIndex{1}\): Distillation Process. (Copyright; 10.22: Distillation - Chemistry Libre Texts)

    During this process, a liquid is heated in a round-bottom flask, and the temperature of its vapor is measured using a thermometer. Once the vapor hits the thermometer bulb, the temperature rises sharply and stabilizes at the liquid’s boiling point. The vapor is then immediately condensed and collected into a separate container. Simple distillation can also be used to purify organic liquids. In this experiment, you will use simple distillation to determine the boiling point of acetone and an unknown organic liquid.

    SAFETY PRECAUTIONS

    1) Always wear chemical splash goggles while working on this experiment.

    2) Work with distillation and all liquids in this experiment under a fume hood.

    3) You are encouraged to wear gloves while handling chemicals.

    4) Dispose of all waste in the proper containers, as your instructor indicates.

    5) Thoroughly clean your work area when finished, and return all equipment and chemicals to the appropriate place.

    CHEMICALS AND EQUIPMENT NEEDED

    Table \(\PageIndex{1}\): Chemicals and Equipment

    CHEMICALS

    EQUIPMENT

    EQUIPMENT

    Benzoic acid

    Watch glass

    Simple distillation apparatus and equipment

    Acetone

    round-bottom flask

    10 mL graduated cylinder

    Unknown organic solid

    Spatula

    Vernier Melt Station (or similar melting point apparatus)

    Unknown organic liquid

    Weigh boat or Weighing paper

    Capillary tubes - for melting point determination

    EXPERIMENTAL PROCEDURE

    Part A: Melting Points

    1) Use a spatula to place a small amount of benzoic acid in a weigh boat or a watch glass.

    2) Pack the benzoic acid into a capillary tube approximately 3 mm in diameter, ensuring it settles to the bottom of the tube.

    3) Insert the capillary tube into the melting point apparatus and determine the melting range of benzoic acid. (Pure benzoic acid melts at approximately 121 - 123 °C.)

    Note: Your instructor will demonstrate how to pack the capillary tube and operate the melting point apparatus.

    4) Dispose of the capillary tube, as indicated by your instructor. Place the excess benzoic acid in the non-halogenated organic waste container.

    5) Repeat steps 1 - 4 for the unknown solid. Based on the melting range, identify the unknown as one of the solids in the table for pre-lab question 2.

    Part B: Boiling Points

    1) Place 10.0 mL of acetone in a 50.0 mL round-bottom flask.

    2) Set up a simple distillation apparatus under the fume hood, and determine the boiling range of acetone. (Acetone boils around 55 - 57 °C.)

    Note: Your instructor will demonstrate how to set up a simple distillation apparatus based on available equipment.

    3) Once you obtain the boiling range of acetone, turn off the heat but allow the water to continue running. (Note: Never distill to dryness.).

    4) Once the glassware is cool, turn off the water, disconnect the round-bottom flasks from the distilling apparatus, and dispose of the acetone in the non-halogenated waste container.

    5) Repeat steps 1 - 4 for the unknown liquid. Based on its boiling range, identify it as one of the liquids in the table for pre-lab question 3.

    PRE-LAB QUESTIONS

    Name: ____________________________________

    1) Explain how melting and boiling points can infer the identity of unknowns.

     

     

     

    2) Consider the following solids and their melting points:

    Table \(\PageIndex{2}\): Melting Points of Known Organic Solids
    Organic Solids

    Melting Points

    Acetaminophen

    168 - 170 ºC

    Acetylsalicylic acid

    135 - 136 ºC

    Anthracene

    214 - 216 ºC

    Vanillin

    81 - 82 ºC

    Resorcinol

    109 - 110 ºC

    Ascorbic acid

    190 -192 ºC

    Acetamide

    79 - 81 ºC

    Urea

    132 - 133 ºC

    Draw the structures for each compound and identify their non-alkane functional groups.

     

     

     

     

     

     

     

     

     

     

    3) Consider the liquids listed below and their boiling points:

    Table \(\PageIndex{3}\): Boiling Points of Known Organic Substances

    Organic Liquids

    Boiling Points

    Toluene

    108 - 110 ºC

    Cyclohexane

    79 - 81 ºC

    Hexane

    67 - 69 ºC

    Methylene chloride

    38 - 40 ºC

    Benzaldehyde

    177 - 179 ºC

    Ethyl acetate

    76 - 78 ºC

    Ethanol

    77 - 79 ºC

    Acetonitrile

    81 - 82 ºC

    Draw the structure of each compound and identify its non-alkane functional groups.

     

     

     

     

     

     

     

     

     

     

    DATA AND OBSERVATIONS

    Name: _________________________Lab Partner(s): ______________________________ 

    Table \(\PageIndex{4}\): Data Table - Melting and Boiling Points of Known and Unknown Organic Compounds

    Measurement

    Temperature

    Melting range of benzoic acid

     

    The melting range of the unknown solid

     

    Possible identity of the solid

     

    The boiling range of acetone

     

    Boiling range of an unknown liquid

     

    Possible identity of the unknown liquid

     

    POST-LAB QUESTIONS

    1.  What was the biggest takeaway from this activity? 

       

       

       

    2. What are some sources of error in this experiment? 

       

       

       

    3. How does your experimental melting point of benzoic acid compare to the actual melting point? What might this tell you about the purity of your benzoic acid sample? 

       

       

       

       

    4. Can you use melting and boiling points alone to identify unknowns positively? Why or why not? 

       

       

       

    5. In addition to melting and boiling points, what other properties can be used to support the identity of an unknown? 

       

       

       

    Please click here to access the Pre-Lab, Data Tables, and Post-Lab in Word or PDF format. Complete them and upload the lab report according to your instructor's instructions.


    This page titled LAB 1- ASSESSMENT OF PHYSICAL PROPERTIES OF ORGANIC COMPOUNDS is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by Saadia Khan.