Dilution and Spectroscopy Lab

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Dilution and Spectroscopy Lab
Lab Word Document
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Dilution Background

• Acids and bases usually come in concentrated
  form, as concentrates, but they are rarely used
  in this form.
• A dilution is prepared by adding a specific
  amount of a concentrate to water to obtain a new
  volume and concentration.
• In order to calculate dilutions of solutions the
  equation
• M1V1 M2V2
• where M is concentration in molarity (mol
  solute/L solution) and V is volume (L), is used

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Dilution Examples

• Dilutions by a factor of 2
• Take 3 mL of acid and dilute with 3 mL of water
• 1 part concentrate, 1 part water
• Dilutions by a factor of 4
• 1 part concentrate, 3 parts water
• Dilutions by a factor of 10
• 1 part concentrate, 9 parts water

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Pipet Instructions
A
E
S

1. Press the A button and squeeze the bulb to
   suck air out
2. Place the pipet into the solution
3. Press the S button to suck the liquid into the
   pipet
4. Take the pipet out of the solution and place it
   into the next cuvette
5. Press the E button to empty the liquid into the
   new cuvette

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Spectroscopy Introduction

• Spectroscopy is one method of determining the
  concentration of an unknown solution.
• By measuring the respective absorbance values for
  solutions with known concentrations, a
  calibration curve can be constructed.
• The absorbance of an unknown can be used to
  determine its concentration through use of this
  calibration curve.

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Absorbance vs. Transmittance

• Transmittance - the fraction of light that is
  transmitted through a sample
• Absorbance - The fraction of light that is
  absorbed by a sample

100 Transmittance
0 Absorbance
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Spec-20 Instrument
Wavelength control knob
Light control knob
Amplifier control knob
Sample holder cover
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Schematic representation of a spectrophotometer
I
Io
Detector
Monochromator
Meter
Light Source (1)
Sample cell (3)
(2)
(4)
(5)
A spectrophotometer is an instrument that
measures the fraction of an incident beam of
light which is transmitted or absorbed by a
sample at a particular wavelength.
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Spec-20 Absorbance
Insert Photograph Spec-20
100 Absorbance 0 Transmittance
Absorbance
0 Absorbance 100 Transmittance
l (wavelength)
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Absorbance of Chlorophyll
1.5
1.2
0.9
Absorbance
0.6
0.3
0.0
300
400
500
600
700
800
Wavelength (nm)
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Amount absorbed
663 nm
400
500
600
700
Wavelength (nm)
Kelter, Carr, Scott, , Chemistry A World of
Choices 1999, page 480
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Calibration Curve
(fixed wavelength)
100 Absorbance 0 Transmittance
out of linear range (too concentrated)
?
Absorbance
0 Absorbance 100 Transmittance
x 2
Concentration
Dilute sample with water 5050. Run sample, read
concentration.
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Dilution of Solutions
Dilution of Solutions  Dilution of Solutions
Dilution of Solutions  Dilution of Solutions
Keys
http//www.unit5.org/chemistry/Solutions.html