Lab Experiment 9 Qualitative Tests for Alkenes

Lab Experiment 9: Qualitative Tests for Alkenes

Aim:  The purpose of this experiment was to use Pyridinium Bromide Perbromide and Potassium Permanganate to test whether a compound is an alkane, alkene, or an aromatic compound. 

Table of Physical Properties and Hazards

Compound

Melting Point (°C)

Hazards

References

Acetone

-95°C

-highly flammable

-irritant

-may cause drowsiness

https://pubchem.ncbi.nlm.nih.gov/compound/acetone#section=Top

Pyridinium Bromide Perbromide

136°C

-Skin irritant

-Lung irritant

-Highly corrosive

https://www.sciencelab.com/msds.php?msdsId=9924762

Potassium Permanganate

240°C

-May intensify fire

-Harmful if swallowed

-causes severe skin burns

https://pubchem.ncbi.nlm.nih.gov/compound/potassium_permanganate#section=Safety-and-Hazards

Procedure & Observation

To begin this portion of the experiment, 9 test tubes were prepared using a variety of different compounds. The compounds used were, 1-Octene, Cyclohexane, Cyclohexene, Kerosene, Ethyl Acetate, Mineral oil, and 3 unknown compounds labeled, Q-I, Q-2, and Q-3.

10 drops of each compound was filled into its labeled test tube. To test the reactions of the compounds with Pyridinium Bromide Perbromide (PBP), 2 drops of PBP was added into each test tube. Some test tubes were observed to turn yellow after adding those 2 drops and were, thus, marked Negative (-). 10 additional drops of PBP were added to the test tubes with compounds that remained clear. Those compounds that remained clear even after the additional 10 drops of PBP were marked positive (+). To test the compounds reaction to Potassium Permanganate (KMnO4), 9 test tubes were filled again with 10 drops of 1-Octene, Cyclohexane, Cyclohexene, Kerosene, Ethyl Acetate, Mineral oil, Q-1, Q-2, and Q-3 separately. 1 mL of Acetone was also filled into each test tube and 20 drops of KMnO4 was added into each tube to observe color change. Some test tubes were observed to turn purple were thus marked negative. The test tubes that were observed to be brown were marked positive.

Results

  1. Reaction with 2% Ethanolic Pyridinium Bromide Perbromide (PBP)

Test Compound

Number of drops of reagent added

Observations

Conclusion

1-Octene

12

Colorless

+

Cyclohexane

2

Yellow

-

Cyclohexene

12

Colorless

+

Ethyl Acetate

2

Yellow

-

Kerosene

12

Yellow

-

Mineral Oil

12

Yellow

-

Q-1

2

Yellow

-

Q-2

12

Colorless

+

Q-3

12

Colorless

+

  1. Reactions with 2% Aqueous KMnO4 Solution

Test Compound

Number of drops of reagent added

Observations

Conclusion

1-Octene

20

Brown

+

Cyclohexane

20

Purple

-

Cyclohexene

20

Brown

+

Ethyl Acetate

20

Purple

-

Kerosene

20

Purple

-

Mineral Oil

20

Purple

-

Q- 1

20

Purple

-

Q- 2

20

Brown

+

Q- 3

20

Brown

+

Conclusion

According to the tables that display both results for PBP and KMnO4, each compound that reacted with both solutions appear to show the same positive and negative results. Positive conclusions of the compounds that reacted with Ethanolic PBP indicated that there was a color change from yellow to colorless (or remained colorless) which means that there was no alkene present in that molecule. Compounds that remained yellow indicated that an alkene was present in that molecule. The compounds reaction to KMnO4 either turned purple or turned into a brown precipitate. The purple test tube solutions indicated that the compound was an alkene. The test tubes that formed the brown precipitate were not alkenes but syn diols were formed after adding KMnO4.

IR

The compounds used in this portion of the experiment were denoted IR-3 and IR-8. IR-3 served as our solid sample, while IR-8 was the liquid sample. The type of spectrometer used in this experiment was ITR machine. The platform of the crystal on the ITR machine was first cleaned with ethanol and a cotton swab to ensure no error in the spectrum. A background check was also authorized on the machine before preparing both IR samples. The solid sample, IR-3, was placed on the crystal on the ITR machine and the compound was then sealed and protected by placing the holding down device on top of the compound. The IR sample was then collected as its spectrum appeared on the computer screen. Once the spectrum was printed, the platform with the crystal was again cleaned with absolute ethanol and wiped using a Kimwipe. In preparing the liquid sample IR-8, another background check was done and a drop of the sample was placed on the crystal in the middle of the platform. The holding down device helped to secure the sample and its data was collected as the spectrum for this sample compound was displayed on the computer. The sensitivity for both samples were set to a 100 before being printed. The major peaks in both spectrums were labeled and both unknown IR samples were identified. 

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