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Topic: Spectrophotometric Titration curve  (Read 9850 times)

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Offline 1stplace

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Spectrophotometric Titration curve
« on: April 19, 2008, 12:44:08 PM »

This is the graph and the previous part to the question that I don't get.

The question is : The spectrophotometer that was used for the titration cannot properly measure differences in light intensity by less than 1%. Using the above data, calculate the minimal concentration of the complex that can be accurately measured.

I really don't know where to start. Can somebody help me?

Offline Arkcon

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Re: Spectrophotometric Titration curve
« Reply #1 on: April 19, 2008, 01:04:34 PM »
So the chart should have error bars of 1%.  Given that, and the shape of the graph, what do you think of the chart?  What range is useful?  What do you think of the shape of the graph?
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline ARGOS++

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Re: Spectrophotometric Titration curve
« Reply #2 on: April 20, 2008, 05:45:21 PM »
Dear Arkcon;

I don’t believe that the “Error-Bars” will be very helpful, because:
  .. differences in light intensity by less than 1%.
  -  is not very linear to Absorptions, but Absorptions is “very” linear to Concentrations!
That means that the “’1.0 %’ -Error-Bars” will have a different size over de whole Absorptions scale.

Dear 1stPlace;

As the second Question asks:
Using the above data, calculate the minimal concentration  . 
    -   it is required to solve prior the first Question, otherwise you will not have any Concentration result!

To solve the 1. Question you best “see” the Spectrometer as only a little special Indicator!
  • -   So, at how much mL’s your “Indicator” has changed its color?
  • -   And the remaining you can handle as a normal  “…….”-Titration: It’s Stoichiometry!

Then to solve the 2. Question you need the Mrs. “Beer and Lambert”, because you will have to translate:
  • -   Your Concentration and corresp. Absorption you have read from the Graph into an of εtotal!
  • -   1.0% Transmittance into its corresponding Absorption (A1.0%).
  • -   Finally you can translate your A1.0% with the help of εtotal into a Concentration.

Mrs. “Beer and Lambert” with Graphs, Formulas, and Explanations you can find on:

I hope this gives you enough help to start your both Solutions.

Good Luck!

P.S.:  For Stoichiometry the following page may be of some help:   "Stoichiometry Problem

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