Absorption spectroscopy and acetic acid

Absorption spectroscopy and acetic unpleasantThe absorbance of light, wavelength 632nm, was measured in an index firmness of purpose at variable pH, and varying dumbness, leaveing for a Beer-Lambert speckle to be constructed. This was then apply to measure acetic acid uptake at the surface of deionised water and octan-1-ol coated water, allowing pH, and indeed tautness, to be calculated from absorbance of the liquid.IntroductionSurfactants are molecules which are able to cultivate a surface across a liquid, and stop the interaction of orthogonal molecules with the solution without interacting with these molecules first. These are extremely useful since they often contain a hydrophobic and hydrophilic aspect, which interact differently to different molecules. Surfactants are used in the manufacture of paper, textiles and construction among others.1 They are the main ingredient of detergents and they allow non-polar 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 force a surface of hydrophobic tails. This will stop polar molecules from ledger entry the liquid, since the liquid will appear to be a poor solution for the polar molecule to interact with. They also increase decrease tightness of the liquid.4This barrier is expected to stop the acetic acid, used in interrupt 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 detect or measured.ExperimentalUsing de-ionised water, a reference light volume 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 use 0.1M sodium hydroxide and glacial acetic acid, and absorbance was noted at pHs amid 3-6 at 0.3 increments. 50ml of remaining solution (1) was further diluted to solutions of 0.0025%, 0.00125%, 0.000625% and 0.0003125% concentration. Spectroscopic digest of these concentrations was made, and a Beer Lambert graph plotted. A solution of unknown concentration was then spectroscopically analysed and its approximate concentration go overd. This solution was then enclosed in a container with acetic acid, and spectroscopic readings taken every 30 seconds. This was retell with fresh solution, with the add-on of 0.2ml of octan-1-ol to the surface of the cuvette.ResultsThe results for the pH change showed a curve, freeing from lower pH on the left to high pH on the right.This is a more(prenominal) quantifiable way of showing that as the Bromocresol saturnine blue at high 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 possible to draw a Beer-Lambert plot expound 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 point it is possible to derive the gradient, and thence the value of ?L. This was determined to be 36600.The Bromocresol solution of unknown concentration transmittable 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 guileless(prenominal) 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 fault analysis and standard errors of instrumentality 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 in all likelihood that in this dimerised arrangement acetic acid more quickly dissolved in the oil, in addition to acetic acid pronto dissolving in organic solvents. Because of these reasons it readily crossed over f rom the relatively non-polar octanol to the polar water solvent, 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 mark 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 give thanks 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 petroleum industry, Cambridge University compaction (2000) pp. 7.R. J. Farn, Chemistry and Technology, Blackwell Publishin g (2006) pp. 6.K. S. Birdi, Handbook of surface and colloid chemistry, 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.