Researcher

Rida Atif

Objective

To determine the room temperature solubility of benzoic acid in ethanol/water (30:70) volume

Procedure

A mixture of ethanol/water was created in a 30:70 volume. About 0.1g of benzoic acid was added into a 1-dram vial along with approximately 1mL of the ethanol/water solution. The vial was attached to an apparatus that submerged it in a 25C water bath while shaking it on the shake plate. The vial was allowed to shake for 30 minutes, then a few drops of the supernatant from the vial was transferred to an inner coaxial NMR tube. An NMR spectra was obtained. The vial was reattached and allowed to shake for 24 hours. After 24 hours, the supernatant was [[#|1000]] fold diluted in methanol and an UV spectrum was obtained of the sample to calculate the concentration.

Results

SAMS Sheet
30 minutes - 0.1416M some phasing issues
20 hours - 0.1374M slight peak distortion

UV Spectra 24 hours 1000 dilution
0.2034M (calculated using Beer's Law)
A=0.205388 (lambda max of 272nm)
Ex. Coeff= 1010 L/mol*cm
length = 1cm

Discussion

The NMR spectrum showed that the concentration of the sample was around 0.14M while is close to the value obtained in the Pal89 paper of 0.12M.
However, when the UV spectrum was taken, the calculated concentration (using Beer's Law) ended up being 0.2M. A possibility of this higher concentration is that acetone was used to wash the cuvette before the sample was put into it. Acetone absorbs in the same area as methanol so this definitely affects the calculated concentration.

Conclusion

The experiment should be done again in which no acetone is used in the process of obtaining the UV spectrum.

Log

2012-07-30

11:57 - Made a solution of ethanol/water (30:70) volume by [[#|mixing]] 1.17g of ethanol and 3.5g of water (mass calculated based on each solvent's density)
12:04 - Added 0.116g of benzoic acid into a 1-dram vial
12:10 - Added 1.113g of the ethanol/water solution (1.162mL based on density of 0.958g/mL)
13:09 - The vial was attached to an apparatus that submerged it in a 25C water bath while shaking it on the shake plate. The shake plate was turned on to setting 2
13:39 - The shake plate was turned off and the vial was removed from the apparatus
13:50 - A few drops of the supernatant were transferrered to an inner coaxial NMR tube
14:00 - The shake plate was turned on again

2012-07-31

9:40 - Turned shake plate off
9:44 - Transferred a few drops of the supernatant into an inner coaxial NMR tube
9:51 - Re-attached vial to shaking apparatus
9:52 - Turned shake plate back on
13:19 - Turned off shake plate.
13:28 - Used a micropipet to transfer 50microliters of the supernatant into a 5mL volumetric flask. The remainder of the flask was filled with methanol to dilute the supernatant.