Unknown Concentration Of Phenol Red Lab Report

Introduction
In this report, an unknown concentration of phenol red and the pKa of an acid were determined. The unknown concentration of the phenol red was determined by using Beer’s Law (A=εbc). According to Beer’s law, the absorbance of a compound is proportional to its concentration. The absorbance of several standard solutions were measured by a spectrometer, and these results supported Beer’s Law. The pKa of an acid was determined by the Henderson-Hasselbalch equation (pH= pKa+ log ([A-]/[HA]). Due to systematic error, the results for determining the pKa were inconsistent.
Experimental
Spectrum Analysis of the Acidic and Basic Forms The absorbance of an acetate buffer and a borate buffer were measured by using a UV-Visible spectrophotometer. To prepare the solutions, Phenol red was added into each test tube, containing the acetate buffer and the borate buffer. The acetate buffer was a clear yellow solution, while the borate buffer was a pink solution. The maximum absorptions of each solution curve were recorded. The curves of each buffer were photographed.

Each solution contained different amounts of distilled water, buffer and phenol red. The absorbance for each sample were measured by a UV-Vis spectrophotometer, in which the fixed wavelength (λ) was set to 550 nm. The absorptions of the standard solutions were graphed into an Absorbance vs. Concentration line graph. The concentration of the unknown was determined by using the Absorbance vs. Concentration