Identification of Aldehydes and Ketones

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Samples

Fehling’s Test

Observations

Acetaldehyde

✔

Green, Homogenous

Butyraldehyde

♒

Light Blue

Benzaldehyde

✘

Blue, No Reaction

Acetone

✘

Blue, No Reaction

Acetophenone

✘

Blue, No Reaction

Unknown

✔

Green, No Reaction

Discussion

The samples were held under several tests to determine the changes and reactions that may occur and to determine the unknown if it was an aldehyde or a ketone.

Under the chromic acid test, the aldehydes tested positive and theses are acetaldehyde, butyraldehyde, and benzaldehyde. The unknown, acetone and acetophenone produced an orange color.

Next, the Tollen’s test, the benzaldehyde and the unknown tested positive although the unknown has a fast reaction and the benzaldehyde had a slow reaction. The butyraldehyde tested false positive because of the formation of white flakes rather than the silver mirror. The acetophenone also tested false positive with the cloudy and immiscible resulting mixture. The acetaldehyde and aceone tested negative. The acetaldehyde was supposed to be positive and was researched that only compounds that lack hydrogens do not respond because it makes it resistant to oxidation. This was recognized as a gross error on the part of the performers.

Next, the iododform test. The acetone and the acetophenone resulted positive which is good since this test is for methyl ketones and both of the samples are methyl ketones. The aldehydes and the unknown tested negative.

Next was the 2,4-Dinitrophenylhydrazine test. The acetaldehyde and the acetone tested positive and the others tested false positive. It is suspected that the addition of the Ethanol (95%) has interfered with the response of the other compounds.

Lastly, the Fehling’s test was conducted and the acetaldehyde and the unknown tested positive and the butyraldehyde tested false positive and the benzaldehyde, acetone and acetophenone tested negative. The benzaldehyde did not react with the Fehling’s reagent since it is an aromatic compound and lacks alpha hydrogen that can oxidize the test reagent.

Conclusion

From the data and results, through very careful and determined analysis and research, the unknown is determined to be an aldehyde since it behaved more closely as an aldehyde rather than a ketone.

Recommendations

It would be inferred that close examination and detailed observation should be done to accurately describe the reaction that took place. And also that to let the test samples stand for a few more minutes or other techniques to make the reaction take place faster.

References

Laboratory Manual

http://www.chem.umass.edu/~samal/269/aak.pdf Retrieved December 9, 2016.

http://chemistry.stackexchange.com/questions/44872/why-does-benzaldehyde-not-respond-to-fehlings-test Retrieved December 9, 2016