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Dilution and Spectroscopy Lab
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LabWord
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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
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
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
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.
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
Spec-20 Instrument
Sample holdercover
Amplifiercontrol knob
Light controlknob
Wavelength control knob
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.
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
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
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
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.
Dilution of Solutions
KeysKeys
Dilution of Solutions Dilution of Solutions
Dilution of Solutions Dilution of Solutions
http://www.unit5.org/chemistry/Solutions.html
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