Purpose of Spectrophotometric Determination of the Dissociation Constant of an Indicator

In this lab report, the objective of this lab is that, to analyze an acid dissociation constant for an indictors by using a Spectrophotometric techniques, acid absorption characteristics of the and base form of the Bromophenol Blue, as an acid base indicators .The opportunities which is applied through the various aspects of the acid-base chemistry’s, for the light absorptions through providing the opportunity.  Spectrophotometric is used to calculate the ionized concentrations basic, as well as unionized acidic forms of indicators that are used on the behalf of determinations for the acid dissociation constant by using the Henderson-Hasselbach equations.

Experimental data of Spectrophotometric Determination of the Dissociation Constant of an Indicator

In this lab experiments, the experimental data proceeded as follows, in the 100ml volumetric flask transferred the 5ml; Bromophenol blue solutions, and also add the 0.05M KHP where its pH is 0.4 buffer solutions to measure the volume of the total exactly 100ml. now close the stopper of the flasks and mix the solutions well, then prepared the two clean 100ml beakers, along with labeling of A, B. Calculate the 50ml solution by using the 50ml graduated cylinders into the every beakers, and also use the pH meter to calculate the pH for the solution A where its pH is same as the pH B. Then calculate the solution of the absorptions spectrums for the A solutions up to 380 to 650nmduring the 109nm intervals, by using the spectrophotometers that is assigned from the laboratory.

During lab, there should be focused on the one student will work on the Solution A and the other will work on the solution B, that students who work on Solution A should label the test tubes A1, A2, A3, in the lab manual that table is provided, according to this add the solution A, KHIP as well as 0.20 M HCL. Exactly calculated the pH of every solution and then calculated the solutions absorbance of A1, A2 at λ1 and λ2 along with the spectrum solution about the 380 to 650nm.when pick the solution A3 then took the clean test tube and label them A4, A5, A6 plus added the solution of the A3 of the 0.20 mHCL regarding to that is provided in the table during lab manual. Those students that is working on the solution B, the entire step is similar expects use of the NaOH instead of the HCL .The deviation which is reported; for B3 data of spectrum is used from Parinaz Irani. “On the behalf of extra information refer to a lab manual. 2  

Results and Calculations

Plot Absorbance vs. Wavelength of Spectrophotometric Determination of the Dissociation Constant of an Indicator

3.1 Absorbance at λ1 vs Concentration of solution A3-A6

λ2 slope = 34206

Slope = Molar Absorptivity Constant

Sample calculation:

3.3 Absorbance at λ2 vs. Concentration of solution B3-B6