CH111- Lab 3
Main idea of the lab- use visible spectrophotometry to explore the equilibrium constant of an indicator.
Key point- not all indicators indicate at pH=7. We will find the "effective range" of your unknown indicator, the range of pH where it IS useful.
Buffers are solutions of acid AND conjugate base which resist changes in pH (think of LeChatelier). We will prepare several buffer solutions and examine the visible spectroscopy of your indicator in these buffers.
In this lab, we are investigating the "absorbance" (symbol: capital A) of buffered indicators, not the "absorbency" of paper towels or sponges. There is no plural or adjective of the term. "Absorbancy" is not a word. "Absorbances" and "absorbancies" are not words. These words have not appeared in your text or any scientific journal, so do not include them in your lab report.
Beer's Law is only valid for dilute solutions and technically only applies for A values between 0.2 and 0.8, so if your values are outside this range....
Does % error have any significance when calculated on the final pH? Consider pH=4.90 actual, pH=4.86 theoretical vs. H+ concentration 10-4.90 actual, 10-4.86 theoretical.
Among others, topics to be sure you cover in your report: indicator theory, buffer theory, spectroscopy in general, visible spectroscopy in particular
Read Skoog Ch. 10, 22, 23, 24
Read Hill Ch. 15
Send questions or comments to Professor Kolack via email (kolack AT cooper DOT edu)
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