Unknown Lab Report

In this experiment my lab partner and I collected an unknown sample (sample A) and performed a series of tests and analyses to determine the chemical composition of the unknown. One of our learning goals was to practice performing the basics of analyzing an unknown; this entails measuring boiling point, melting point, and noting its physical properties (color, smell, etc.) In addition to this, we also practiced reading basic spectra, looking at and interpreting test results, synthesizing derivatives of our unknown, and testing the melting point of said derivatives to help us further identify our unknown.
When we obtained our sample, we noted it’s physical characteristics. It was a clear liquid, and had a particular odor; I thought it smelled

like crushed up vegetables (spinach?), while my lab partner thought it smelled of cardboard. We performed our first test by measuring the boiling point, which came out to approximately 147°C.
i.

Our first test to perform was the potassium permanganate / Baeyer test, to test for unsaturation. We mixed in ethanol, our unknown, and some of the KMnO4 solution. The initial pink color of our mixture turned to a golden brown color which indicated a positive test result. If our test gave a negative result, the solution would have remained a pink color (small amounts of brown precipitate might have formed). Below is a diagram of the positive test result:

ii. Our second test to perform was a chromic acid test, to test for the presence of alcohols. We mixed in acetone, our unknown, and some of the chromic acid reagent. After mixing, our initial orange color changed to a blue-green hue pretty quickly; this indicates a positive test result. Because we had a positive test result, this indicates the presence of primary and secondary alcohols in our unknown. If our test yielded a negative result, the solution would have remained an orange color indicating the presence of tertiary alcohols or no alcohols. Below is a diagram of the positive test

result:

iii. Our third test to perform was an Iodoform test, to test for the presence of methyl ketones. We mixed in methanol, NaOH, our unknown, and the iodine/KI solution. After mixing, we had a pretty solid yellow color which indicated a positive test result. If our test yielded a negative result, we would have had a brown solution and no yellow precipitate. Below is a diagram of the positive test result:

iv. Our fourth and final test to perform was a Schiff’s Fuchsine Aldehyde test, to test for the presence of aldehydes. We mixed in the Schiff’s reagent and a drop of our unknown. After mixing the solution and letting it sit for 10 or so minutes, we had a faintly pink-purple solution which indicated a positive test result. If our test yielded a negative result, we would have had a colorless solution. Below is the structure of the Schiff’s Fuchsine reagent:

When observing the IR spectrum of our Unknown A, we observed three distinct peaks.

One was the typical alkane peak at ~2900/3000 cm-1. Another peak was slightly to the right of our first peak at ~2850 cm-1 which indicates an aldehyde (the C-H bond). Another peak was observed at around ~1710 cm-1 which indicates yet again the presence of an aldehyde (the C=O bond).
After observing that all of our test results were positive, we knew that in our compound unsaturation was present, there were primary or secondary alcohols, methyl ketones, and an aldehyde. Keeping this in the back of our minds, we grabbed the derivatives and tested the melting points of each. When determining the melting point of the 2,4-dinitrophenylhydrazone derivative, we observed it to be exactly at 106°C. With this in mind, we also tested the melting point of our semicarbazone derivative, which turned out to be around ~101°C. After obtaining these numbers, we took a look at the Table J.1 and found the numbers that matched up best with our IR results, various tests, and melting point results. We determined that our Unknown sample A was actually Octanal; the structure of which is drawn

below:

After completing this experiment, my lab partner and I both felt that we learned a lot about the entire process of analyzing. We felt that our analysis skills were very much solidified; skills ranging from observing IR spectra, to performing various tests on the unknown. After observing what we did, I think it is safe to say that we are confident in our inference. This lab provided a good first step into the practical applications of organic chemistry, and was exciting overall.