Absorption spectroscopy and acetic acid

Absorption spectroscopy and acetic corrosiveThe absorbance of light, wavelength 632nm, was measured in an indicant solution at varying pH, and varying compactness, allowing for a Beer-Lambert plot to be constructed. This was thence used to measure acetic acid uptake at the surface of deionised irrigate and octan-1-ol surface water, allowing pH, and hence concentration, to be calculated from absorbance of the liquid.IntroductionSurfactants ar molecules which are able to form a surface across a liquid, and stop the interaction of foreign molecules with the solution without interacting with these molecules first. These are extremely useful since they frequently contain a hydrophobic and hydrophilic facet, which interact differently to different molecules. Surfactants are used in the manufacture of paper, textiles and construction among others.1 They are the main broker of detergents and they allow non- wintry molecules to dissolve in polar molecules, such as oil into water.On the surface of the liquid, the surfactant will interact slightly differently. It will develop a surface of hydrophobic tails. This will stop polar molecules from entering the liquid, since the liquid will appear to be a poor solution for the polar molecule to interact with. They similarly increase decrease tension of the liquid.4This barrier is expected to stop the acetic acid, used in part 3 of the experiment, interacting with the water solvent. If it does interact, the pH of the solution will lower due to acetic acids presence, and the indicator will show a change in colour. If no acetic acid enters the solution, no change should be observed or measured.ExperimentalUsing de-ionised water, a reference light intensity was recorded. A 250ml solution (1) of 0.005% wt bromocresol green was then prepared, and absorbance was measured. 100ml was removed, and the pH adjusted using 0.1M sodium hydroxide and glacial acetic acid, and absorbance was noted at pHs between 3-6 at 0.3 increments . 50ml of remaining solution (1) was further cut to solutions of 0.0025%, 0.00125%, 0.000625% and 0.0003125% concentration. Spectroscopic analysis of these concentrations was made, and a Beer Lambert graph plotted. A solution of unknown concentration was then spectroscopically analysed and its approximate concentration determined. This solution was then cover in a container with acetic acid, and spectroscopic readings taken every 30 seconds. This was repeated with fresh solution, with the addition of 0.2ml of octan-1-ol to the surface of the cuvette.ResultsThe results for the pH change showed a curve, handout from lower pH on the left to high pH on the right.This is a more quantifiable way of showing that as the Bromocresol turned grim at higher pH. This shows absorption toward the end of the spectrum of lower energy, (ie higher wavelength). So as pH increased, the absorbance of Bromocresol at 632nm increased too as it became blue.The next aspect of the experiment was to analyse how concentration affected the absorbance of Bromocresol green. As concentration of bromocresol green was altered, it was manageable to draw a Beer-Lambert plot detailing how the absorption of the light changed with concentration of the Bromocresol Green.As would be expected, there is a straight line relationship between Bromocresol concentration and Absorbance except at higher concentrations, where the solution plateaus and becomes non-linear. Excluding this end dapple it is possible to derive the side, and hence the value of ?L. This was determined to be 36600.The Bromocresol solution of unknown concentration transmitted 0.222, making a LOG(Io/I) value of 0.67. Dividing this by the gradient gave the Bromocresol solution concentration to be 4.5710-6moldm-3.From this it is possible to determine the acidity of the solution using the Beer-Lambert plot as given above. Using an original pH, it is then possible to determine the concentration of the acetic acid on top of this, using s imple equations associated with pKa and pH.From the information of Ka and pH, it is possible to calculate the concentration of acetic acid in the solvent.Error analysisUsing error analysis and standard errors of instrumentation used, it is possible to construct the same graphs as above but with error bars. These are shown below.DiscussionThe calculations and graphs suggest that coating a solvent in octan-1-ol would encourage uptake of acetic acid, rather than inhibit it. This may be due to dimerzation or trimerzation of acetic acid (1) as it evaporates from the surface, making it more soluble in the partially polar octan-1-ol solution.Single carbon-oxygen bonds display less polarisation than carbonyl bonds do, and so it is likely that in this dimerised arrangement acetic acid more readily dissolved in the oil, in addition to acetic acid readily profligacy in organic solvents. Because of these reasons it readily crossed over from the relatively non-polar octanol to the polar water s olvent, decreasing the pH of the Bromocresol containing solution in both the uncoated and octanol coated solutions.It is, however, most likely that the experiment was not successful. Alternative indicators, such as NH3, would have readily dissolved in water and increased the pH of the solution. It would also not have been able to dissolve in the octanol due to the higher polarity and availability of the nitrogen lone pair. Because of this it would have been a better indicator of the presence of a surfactant than acetic acid.AcknowledgementsI would like to thank my demonstrators M. Azwani Mat Lazim and Miss Olesya Myakonkaya for their advice on the experiment.ReferencesR. J. Farn, Chemistry and Technology, Blackwell Publishing (2006) pp. 6.L. L. Schramm, Surfactants fundamentals and applications in the vegetable oil industry, Cambridge University Press (2000) pp. 7.R. J. Farn, Chemistry and Technology, Blackwell Publishing (2006) pp. 6.K. S. Birdi, Handbook of surface and colloid ch emistry, CRC Press (1997) pp. 338.P. Atkins, J. De Paulo, Atkins Physical Chemistry 8th Edition, Oxford Publishing (2006) pp. 432.P. M. S Monk, Physical chemistry understanding our chemical world, John Wiley Sons (2004) pp. 225.V. H. Agreda, J. R. Zoeller, Acetic acid and its derivatives Volume 49 of Chemical industries, CRC Press (1993) pp. 96.