Acids, Bases, and Buffers 1: Monoprotic and Polyprotic Acids Overview Getting Started Techniques Procedure FAQ Full Lab Manual Introduction & Goals Chemistry & Background Key Questions Prelab Problems Safety Procedure In Your Write-up Experiments Index ChemLab Home		FAQ Index Question 1 Why do I have to plot the titration curve? It seems like busy work! Question 2 The pKa values I get from my experiment are different from the ones in the lab manual. Did I do something wrong? Submissions Submit a question or an answer to the FAQ Questions & Answers Question 1 Why do I have to plot the titration curve? It seems like busy work! Professor Milde If you plot the titration curve, you can see graphically how the pH is changing, as you do the experiment. This can enable you to change the frequency of your pH measurements in response to the shape of the curve. It can allow you to improve your data, before it is too late. You can also learn about the titration curve, as you do the experiment, rather than afterwards. This is a better way to understand the concepts and think about your lab work while you are doing it, rather than afterwards. Question 2 The pKa values I get from my experiment are different from the ones in the lab manual. Did I do something wrong? Professor Milde Probably not. The pKa values in the manual are for infinite dilution of the ions. In your experiment, the presence of other ions in solution, or the ionic strength, changes the values of the equilibrium constants. Because of the attraction between the species in equilibrium and the ions in solution, ions with a larger charge are stabilized, in comparision to the same ions in infinitely dilute solution. So each equilibrium is shifted slightly toward the ion with a higher charge. Examine the pKa values you obtained and see if their shift is in the direction that this hypothesis would predict. Include this in the discussion of your lab report and impress your TA! Submissions Submit to the FAQ You can submit either a question or an answer to a question about this week's experiment. Your submission will be mailed to the site editor, who will respond to you directly and also add your submission to the FAQ page. Having trouble with the submission procedure? Check your Kerberos installation. If you lose the FAQ Submission window it may be hidden behind another browser window.
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