Lab report exp4.docx - SECTION MARKS GIVEN MAX MARKS...

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CHM110H5F LAB REPORTExperiment #4 – SPECTROPHOTOMETRICDETERMINATION OF THE DISSOCIATIONCONSTANT OF AN INDICATOR November 2017 November 2017SECTIONMARKS GIVENMAX. MARKSPre-lab questionsPre-lab quizPurposeExperimental methodCollection of dataResults and calculations AccuracyDiscussionsLearning objectivesConclusionsReferences Experimental techniqueReport presentation TOTAL MARKS
PurposeThe purpose of experiment 4 was to experimentally determine the dissociation constant (KIN) andpKINof bromophenol blue indicator spectrophotometrically, through quantitative analysis. Bromophenol blue is used to help detect weak acids and bases. In its acidic form HIn, this indicator will turn yellow, and in its basic form, In-, it will turn blue. Spectrophotometry is used to measure how much a solution absorbs light by measuring the intensity of light as a beam passes through the substance/solution. It detects colour changes that wouldn’t be visible to the naked eye. Using the Beer-Lambert Law to find the molar absorptivity constant, it is possible to measure the absorption strength of a species at any wavelength. According to the law, the absorbance of light at a particular wavelength is directly proportional to the concentration of the form of the indicator that absorbs light at that wavelength. The following reactions are used to determine the dissociation constant, KIn: +¿¿+H3O¿HIn+H2O ↔I n¿a proton from a hydroxyl group is lost in this reaction, for which;+¿H3O¿¿¿I n¿¿¿K¿=¿¿I n¿¿pK¿=pH+log[HIn]¿The value of pKINof the bromophenol blue can therefore be found using the dissociation constant KIN. Answering the pre-lab questions for this experiment aided in our understanding that
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the bromophenol blue absorbed different wavelengths of light depending on its colour and its basic/acidic state at the time. This report outlines the method, data/results, calculations used and learning objectives achieved from this experiment as well as discusses the conclusions that were drawn.Experimental method This experiment was conducted in accordance with the CHM1105F Course Manual without any significant deviations. The first part of the method included the preparation of the solution to be used in the experiment, finding the pH of this solution and calibrating and operating the spectrophotometer to find the absorption spectrum of the solution from 380nm to 650nm and

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