Skip to main content
Try Wikispaces Classroom now.
Brand new from Wikispaces.
Pages and Files
list of experiments
Solubility book (3rd Edn)
To generate a solubility-temperature curve for
Solutions of known concentration of 4-nitrobenzaldehyde in methanol were made by weighing out a known amount of methanol, approximately one gram, in a tared half-dram vial. Weighed amounts of 4-nitrobenzaldehyde were added to each vial. Each vial was tightly capped and parafilmed, and a "flag" was attached to each vial by wrapping copper wire around the vial and attaching a sticker labelled 1 through 7 to each vial. Vials were sonicated in a water bath until the water reached 40.0C, and the vials with remaining solid were removed. The remaining vials were left in the water bath to cool by adding cool tap water, ice water, and ice. When precipitate formed in a vial, the temperature was noted and the vial was removed. Calcium chloride was added to the bath to bring the bath below 0.0C, but without much success.
Sample Vial 6A
Sample Vial 7A
Pure Sample 4-nitrobenzaldehyde
The NMR for Vial 7A showed about 50% conversion the the methanol hemiacetal. This renders any results from this experiment unusable. It is unclear if
Maccarone, E; Perrini, G. Gazzetta Chimica Italiana vol 112 p 447 (1982)
who performed solubility measurments of 4-nitrobenzaldehyde in methanol accounted for this possibility. In our work the solutions were heated to 40C for just a few hours while Maccarone heated one of their solutions to 40C for 24 hours. The images below are the NMR spectra of vial 7A in CDCl3. The spectra showed twice the number of aromatic peaks found in just 4-nitrobenzaldehyde plus additional peaks at 3.5ppm, 5.7ppm, and 6.8ppm. After further research, it was found that the peaks corresponded to those of a hemiacetal, thus the conclusion was made that the contaminant in each vial was not one from the sample solute, but from the solute under going a reaction to form a new hemiacetal compound. Having two different compounds in methanol with presumably two different solubilities thus makes it impossible to determine when the aldehyde is precipitating instead of the hemiacetal. Because of this, no temperature measurements could be made and the solubility-temperature graph could not be generated.
The solubility-temperature graph was unable to be generated from this experiment due to reaction of the solute with the solvent.
09:36--Weighed out approximately one gram of methanol in vials 1, 2, 3, 4, 5, 6, and 7.
09:58--Various amounts of 4-nitrobenzaldehyde were weighed out on weighing paper and carefully added to each vial. After the 4-nitrobenzaldehyde was added, each vial was tightly capped
10:35--All vials were covered with parafilm to prevent any potential evaporation
10:39--All vials were labeled; copper wire was wrapped around the neck of each vial and stickers, labeled 1, 2, 3, 4, 5, 6, and 7, were attached to the end of the wire. This method prevented any marker from washing off and clearly labeled each vial to prevent any confusion.
11:07--All vials were added to the sonicator, half-filled with water, and sonicated until the temperature reached 41.0C.
11:46--Only vials 7, 1, and 2 had dissolved all of the 4-nitrobenzaldehyde. Vials 3, 4, 5, and 6 were removed from the sonicator as they were saturated.
11:49--40mL of cool tap water was added to the sonicator every minute. The sonicator was stirred with a thermometer and the vials were sonicated for approximately ten seconds. Water was periodically removed from the sonicator so the sonication was still effective and the addition of cool water lower effectively lowered the temperature of the bath. This process continued until the sonicator reached 24.0C. After the temperature dropped one degree, vial 2 was inspected to see if precipitation had begun.
12:35--40mL of cold ice water was added to the sonicator every minute.The sonicator was stirred with a thermometer and the vials were sonicated for approximately ten seconds. Water was periodically removed from the sonicator so the sonication was still effective and the addition of cool water lower effectively lowered the temperature of the bath. This process continued until the sonicator reached 6.0C.After the temperature dropped one degree, vial 2 was inspected to see if precipitation had begun.
13:01--Ice cubes were added to the sonicator every minute.The sonicator was stirred with a thermometer and the vials were sonicated for approximately ten seconds. Water was periodically removed from the sonicator so the sonication was still effective and the addition of cool water lower effectively lowered the temperature of the bath. This process continued until the sonicator reached 1.0C. After the temperature dropped one degree, vial 2 was inspected to see if precipitation had begun.
13:35--Calcium chloride was added to the bath in an attempt to lower the temperature of the bath. However, the heat generated by adding the calcium chloride made it too difficult to lower the temperate any further than -1.0C. Vial 2 did not precipitate at -1.0C, so the experiment was concluded.
9:24--It was observed that all vials had formed precipitate after the vials had sat out overnight and come to room temperature. Thus yesterday's prediction that vials 1, 2, and 7 did not form precipitate even at -1.0C was proven incorrect.
9:45--All vials were re-heated to 40.0C in the sonicator. It was observed that all vials were yellow and were not cloudy at 40.0C.
10:23--The sonicator was turned off, allowing the samples to cool in the water bath. Precipitate quickly formed in each vial, though when shaken the vials became cloudy and the precipitate may have gone back into solution; it was therefore too difficult to tell whether or not the solutions were saturated.
12:01--All vials remained in the bath at 18.0C as the cloudiness of the vials remained problematic in determining the saturation of the solution. It was assumed there may have been a contaminant in the vials--an acetal or carboxylic acid may have formed if the aldehyde was oxidized.
12:02--Vials 6 and 7 were centrifuged to separate the precipitate from the liquid. Some liquid was drawn from each vial, placed in new vials 6A and 7A, and set back in the water bath.
12:17--Vials 6A and 7A showed no precipitate at 6.0C, saturation of solution did not change during cooling made no sense. It was again suggested that there was contaminant in the vials.
1:20--NMR tubes were prepared for samples from vials 6A and 7A to inspect the purity of the compounds. 100uL of liquid were drawn from each vial and added to 500uL of CDCl3 in corresponding NMR tubes labeled "6" and "7".
9:35--Sample of 4-nitrobenzaldehyde was dissolved in CDCl3 in an NMR tube.
9:38--NMR of pure sample, vial 6 sample, and vial 7 sample was taken on the 500MHz Varian instrument.
help on how to format text
Turn off "Getting Started"