Objective

To estimate the amount of solute dissolved in a saturated solution of 4-chlorobenzaldehyde in chloroform and methanol, by UV spectroscopy.This experiment is also copied on ONSchallenge Exp006

Procedure

Known concentrations of 4-chlorobenzaldehyde is made-up in chloroform and methanol. A UV spectrum of a further diluted solutions of each is obtained to determine the λmax (wavelength of maximum absorbance) of the solution, using which absorbance of solutions of different concentrations is obtained. The solutions are made by diluting the previously prepared solutions. From the absorbance values, the molar extinction coefficient (molar absorptivity) ε, is calculated using Beer's law A = εcl, by determining the slope of a plot of absorbance Vs concentration. Once the molar absorptivity is obtained the absorbance and thereby concentration of the saturated solution is determined. This is done by obtaining the absorbance of dilute solutions (known dilution) of the saturated solutions of 4-chlorobenzaldehyde in chloroform and methanol.

Results

UV Spectrum
4-Chlorobenzaldehyde - CHCl3
Overlay CHCl3 solutions of 213A-2, 213A-3, 213A-4, 213A-5 and 213A-6
Overlay CH3OH solutions of 213A-2, 213B-3, 213B-4, 213B-5, 213B-6

Spreadsheet

Discussion


Conclusion


Log


2008-11-10

13:22 Weighed out 4-chlorobenzaldehyde 140.51mg (for solution 211A in CHCl3); 9.9959mM.
13:40 Weighed out 4-chlorobenzaldehyde 140.54mg (for solution 211B in CH3OH); 9.9980mM
14:00 Made-up 100mL solutions of 4-chlorobenzaldehyde 213A (in Chloroform using 140.51mg) and 213B (in Methanol using 140.54mg).
16:00 Made-up five dilute solutions using 213A, the new solutions are 213A-2, 213A-3, 213A-4, 213A-5 and 213A-6 in chloroform in 10mL volumetric flasks. The concentration of each solution is listed in the spreadsheet Exp213-WS1

2008-11-13

18:00 Obtained UV Wavelength scan for chloroform solution (213A dilute solutions)
19:00 Obtained absorbance for the chloroform solutions (213A dilute solutions).

2008-11-15

16:00 Made-up five dilute solutions using 213B, the new solutions are 213A-2, 213B-3, 213B-4, 213B-5, 213B-6 in methanol in 10mL volumetric flasks. The concentration of each solution is listed in the spreadsheet Exp213-WS1
17:20 Obtained UV Wavelength scan for methanol solution (213B dilute solutions)
20:00 Obtained absorbance for the methanol solutions (213B dilute solutions).

2008-11-16

12:00 Dissolved 4-chlorobenzaldehyde in chloroform (700uL), vortexed it (1min) added more solute, vortexed another minute..the solution became saturated, centrifuged for 30s, this solution is 213E..
12:30 Dissolved 4-chlorbenzaldehyde in methanol (700uL) vortexed (45s), added more solute, vortexed (1min) the solution became saturated, centrifuged for 30s, this is solution 213F
13:00 Made-up a solution 213E-2 (100mL) by homogenizing 50uL of 213E in chloroform in a 100mL volumetric flask.
13:30 Made-up a solution 213F-2 (5mL) by homogenizing 200uL of 213F in methanol in a 5mL volumetric flask.