Experiment 3 Spectrophotometric Determination of pKa

Goals- Two Weeks Overall- The indicator is a ________ that is a different ____ for acid(HIn) and conj. base(In - ) forms Will be determined by plotting __________________ Week One We have a ________________ mixture, HIn and In - Need to determine ____ values so that equation 10 can be used to determine __________ Determine ______________ using ________for given unknown (I will provide these) Use the _______________ to determine ________ by making _________________ for standard solutions at chosen wavelengths

Beer’s Law Plots???? Beer’s Law _____________  =extinction coefficient or molar absorbtivity, a constant for a particular material at a given wavelength  ’ 1HIn =  ’ for HIn at wavelength 1 b=pathlength, constant for our experiment because using one cuvet, =1cm c=_________________ of the species in the solution that is in the cuvet A=  bc is __________________________________ Beer’s Law Plot Plotting ____________ Can be used to determine______ (the _____ for the plotted data, the m because c is our x)

The Steps Make four “standard” concentration solutions in ____ Using graduated pipets and volumetric flasks What are the concentrations of these solutions after you prepare them? 40mL of 0.25M H + diluted to 100mL

LeChatelier LeChatelier shift ensures that when in acid [HIn]/[In - ] is ________ LeChatelier shift ensures that when in base [HIn]/[In - ] is __________ What does this do for us? Why are we preparing in acid and base?

16 measurements (4 concentrations of indicator in acid + 4 concentrations of indicator in base) *2 selected wavelengths = 16 _____result values from ___ plotted lines Plots can be on one graph Please use different symbols to distinguish between the lines because colors do not show on b&w printer Data