LAB 1- ASSESSMENT OF PHYSICAL PROPERTIES OF ORGANIC COMPOUNDS
- Page ID
- 506258
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Determination of Melting and Boiling Points of Organic Compounds
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.
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.
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
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:
| 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:
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): ______________________________
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
- What was the biggest takeaway from this activity?
- What are some sources of error in this experiment?
- 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?
- Can you use melting and boiling points alone to identify unknowns positively? Why or why not?
- 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.


