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Unformatted text preview: e of Acetic Acid
Solution Added (mL) Absorbance
λmax = ______________ nm. This is the wavelength having the largest absorbance of all the data you
took for the basic form in the above tables. Department of Physical Sciences Kingsborough Community College The City University of New York Spring 2012
Experiment 6: Determination of the Equilibrium Constant for Bromocresol Green 7 Calculations
We will use graphical analysis to produce an absorbance spectrum of bromocresol green in basic and
acidic solutions. Both spectra should be represented on the same chart. Vernier Graphical Analysis and
Microsoft Excel are appropriate programs for this exercise. The instructions below are for Graphical
1. Open Graphical Analysis on the computer.
2. Enter the combined absorbance data for the acidic form and base formic. Sort the data by wavelength.
Label this data column (y-axis) “basic form”and enter “absorbance” for the units. Label the x-axis
“wavelength” with units of “nm.”
3. To graph the acidic form absorbance values in Graphical Analysis, you will need to add a second
column to the Data Table Window. Do this by selecting New Column in the Data menu and choosing
Manually Entered. Label the acidic data “acidic form” and enter “absorbance” for the units.
Choose different point protectors for each of the two absorbance curves. Put a legend on the graph. This
way you will be able to distinguish the curves.
4. You have now plotted two absorption spectra for bromocresol green—the blue basic form and the
yellow acidic form. Also, in addition to AI and AII, you should have a precise measurement of the
absorbance (Ax) of the bromocresol green solution at four different pH values. All these measurements
have been taken at λmax, the wavelength where the absorbance of the basic form of the indicator is at a
maximum and the absorbance of the acidic form is very low. The next three pages can be used to perform
the series of calculations required to find Ka for bromocresol green. Department of Physical Sciences Kingsborough Community College The City University of New York Spring 2012
Experiment 6: Determination of the Equilibrium Constant for Bromocresol Green 8 Name Partner Partner 1. Finding the number of moles of sodium acetate (NaC2H3O2) in solution A
Molarity of sodium acetate solution on bottle
Volume of sodium acetate solution used in dilution in milliliters
Volume of sodium acetate s...
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