Unformatted text preview: the ratio of the extinction coefficients at these wavelengths. The algebra is somewhat complicated, but it can be shown that: (
" "A
%% +
* Aλ 2 − $ Aλ1 $ λ 2,acidic '' $
'
[ In − ] Aλ1,acidic *
# # Aλ1,acidic && =
.* "
"A
%% [ HIn ] Aλ 2,basic *
λ 1, basic
A −$A $
''
* λ1 $ λ 2 # Aλ 2,basic &' #
&,
) (11) It is better to use equation 11 when analyzing your data as opposed to the derived equation 10 above. POSSIBLE QUIZ QUESTIONS 1. What is the objective of this experiment? What is being measured? How will the data collected be used to determine the final result? 2.
3. What two variables will be plotted in order to determine the pKa of the unknown indicator? How will the relative concentrations of the acidic and basic forms of the indicator be determined? 4. Given the following data, determine [In ] . Each solution contains the same amount of the indicator " [HIn] bromothymol blue. Sample 1 2 3 5.
6. ! Measured pH 1.0 6.85 13 A, 430 nm 1.097 0.7333    A, 555 nm    0.569 1.428 How would you prepare 50 mL of a 0.20 M solution starting with solid NaH2PO4.H2O? How would you prepare 50 mL of a 0.20 M solution starting with solid Na2HPO4.7H2O? MATERIALS & METHODS Preparation of a Buffer Series Work in groups of 4 1. Obtain a. Eight 50 mL volumetric flasks (depending on the number of flasks in the room, you might need to use four then make solutions for the other four samples) b. Two 5.0 mL graduated measuring pipettes (one for each phosphate solution) c....
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 Summer '08
 Dr.Brooks
 pH

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