Visible Spectrophotometer

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Visible Spectrophotometer
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Visible Spectrophotometer
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Visible Spectrophotometer
100 Adjust
I0
I
white light
detector/recorder
100 adjust blank distilled water
prism
I0 I transmittance (I / I0) x 100
100 absorbance 0
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Visible Spectrophotometer
Zero Adjust
I0
I
white light
detector/recorder
zero adjust (barrier inserted)
prism
I 0 transmittance 0 absorbance maximum
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Visible Spectrophotometer
Sample
I0
I
white light
detector/recorder
sample solution
prism
I lt I0 transmittance (I / I0) x 100
50 absorbance 1.7
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Visible Spectrophotometer
I0
I
white light
detector/recorder
sample solution
prism
I0 I transmittance (I0 / I) x 100
100 absorbance 0
In order for blue solution to absorb light,
wavelength must be changed to blues complement
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Visible Spectrophotometer
white light
I0
I
detector/recorder
sample solution
prism
Wavelength is changed by either rotating prism
or position of slit
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Spec 20 Visible Spectrophotometer
digital
analog
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1. Adjust wavelength
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2. Zero adjust with sample compartment empty
0 T
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3. 100 adjust with distilled water (blank)
in sample compartment 100 transmittance
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4. Record sample absorbance (Be certain to
switch MODE to absorbance)
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Beers Law

• As the intensity of the color of the sample
  solution increases
• the absorbance increases.
• A ? b c

absorbance
constant
path length
concentration
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Determination of the Concentration of an Unknown
Solution

• Prepare a set of standard solutions of known
  concentrations
• Select the appropriate wavelength
• Determine the absorbance of each
• Determine the absorbance of the unknown solution

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(No Transcript)
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13 ppm
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Recall Beers Law
A ? b c
0
y mx b
.0051 0.00037 x C 0.00030
13.0