Unknown Aldehyde Or Ketone Lab Report

Identifying an Unknown Aldehyde or Ketone

Introduction

The purpose of this lab is to identify an unknown aldehyde or ketone substance using chemical tests. The chemical tests used in this experiment are solubility, Schiff, Bisulfite, and Iodoform tests. Also, a 2,4-dinitrophenylhydrazone derivative synthesis reaction will be completed from which a melting point will be obtained. The chemical test results and the melting point analysis will be compared to the table of compounds given to find the unknown’s identity1.

Experimental

An unknown substance labeled Unknown 2 was obtained.
Solubility test:
Water (1 ml) was added to a test tube, and then the unknown (2-3 drops) were also added to the test tube. A pipet was used to blow bubbles
The unknown (0.05 g) was added. The mixed solution was observed to be an orange color. A cap was placed onto the vial. A water bath was used to warm the mixture for five to ten minutes. In the first five minutes of the test, not a lot of precipitate had formed. So, the capped vial was tapped, and then let sit repeatedly until enough precipitate formed. Precipitate was observed forming more and more as the solution heated and time passed. The solution was let sit to cool to room temperature, and then placed into an ice bath for a couple minutes. Vacuum filtration was used to collect crystals while a lot of water was used to wash. A small piece of litmus paper was used to check the crystal’s pH. Vacuum filtration with water as a wash was utilized to wash the crystals until they turned basic. Then, the crystals were dried with filter papers. After fully dried, the precipitate was a dark orange color. The precipitate was weighed. (0.128 g) Now, in a new 15 ml plastic conical vial, the product was recrystallized from ethanol (9 ml, 154 mmol). The precipitate that formed was a cloudy orange color. The product was weighed and a melting point analysis completed. (0.049 g): mp
For the solubility test, the solution was observed to turn cloudy white and oil-like bubbles formed at the top of the solution, so Unknown 2 is insoluable. The Schiff test results were that the solution immediately turned the color magenta signifying that aldehydes are present in Unknown 2. The bisulfite test first required the addition of methanol to make the solution soluble because our unknown was shown to be insoluable from the solubility test results. The bisulfite test results were that a white precipitate formed at the top, which signified that aldehydes, unhindered cyclic ketones, or unhindered methyl ketones are part of Unknown 2. The Iodoform test showed that methyl ketones are not present in Unknown 2 because no yellow solid iodoform precipitate formed. The 2,4-dinitrophenylhydrazone derivative’s melting point found was 104-105 oC. So from all these tests, Unknown 2 was found to be insoluable, contain aldehydes, not contain methyl ketones, and have a melting point around 104-105 oC. Looking at the table of compounds that the unknowns could be in Table 3.1, there are only three compounds that contain aldehydes and are insoluable, which are benzaldehyde, n-Heptanal, and cinnamaldehyde. Out of these three compounds, only n-Heptanal is close to the melting point found. The reason that n-Heptanal’s melting point of 108oC is slightly off from the experimental melting point range found of 104-105 oC could be from a small amount of