dilution and spectroscopy lab lab word document lab word document
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Dilution and Spectroscopy Lab
LabWord
Document
LabWord
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
1. Press the A button and squeeze the bulb to suck air out
2. Place the pipet into the solution3. Press the S button to suck the liquid
into the pipet4. Take the pipet out of the solution and
place it into the next cuvette5. Press the E button to empty the liquid
into the new cuvette
AE
S
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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
Sample holdercover
Amplifiercontrol knob
Light controlknob
Wavelength control knob
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Schematic representation of a spectrophotometer
Detector
Sample-holder
Meter
Zero adjustand power control
Wavelength scale
Wavelength control
Light control
Monochromator
LightSource
(1)
Samplecell
(3)(2) (4) (5)
Io I
Meter
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
l (wavelength)
Absorbance
100 % Absorbance 0 % Transmittance
0 % Absorbance100 % Transmittance
Insert Photograph
Spec-20
Sample-holder
Meter
Zero adjustand power control
Wavelength scale
Wavelength control
Light control
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1.5
1.2
0.9
0.6
0.3
0.0300 400 500 600 700 800
Wavelength (nm)
Abs
orb
ance
Absorbance of Chlorophyll
1026 1024 1022 1020 1018 1016 1014 1010 108 106 104 102 1
10-8 10-6 10-4 10-2 1 102 104 106 108 1010 1012 1014 1016
Frequency (Hz)
Wavelength (nm)
cosmicrays
gammarays
x-rays ultra-violet
infra-red
radio(microwave)
radar tele-vision
radio powertransmission
Violet Blue Green Yellow Orange RedUV
NearInfrared
400 nm 500 nm 600 nm 700 nm
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Kelter, Carr, Scott, , Chemistry: A World of Choices 1999, page 480
Am
ou
nt a
bso
rbe
d
663 nm
Wavelength (nm)400 500 600 700
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Calibration Curve
Concentration
Absorbance
100 % Absorbance 0 % Transmittance
0 % Absorbance100 % Transmittance
out of linear range(too concentrated)
x 2
(fixed wavelength)
?
Dilute sample with water 50:50. Run sample, read concentration.
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Dilution of Solutions
KeysKeys
Dilution of Solutions Dilution of Solutions
Dilution of Solutions Dilution of Solutions
http://www.unit5.org/chemistry/Solutions.html