Serial Dilution Activity Using a pipet Simulated Acid: Red =
nitric acid Yellow = sulfuric acid Blue = hydrochloric acid Slide 2
Spec-20 Instrument Sample holder cover Amplifier control knob Light
control knob Wavelength control knob Slide 3 Spec-20 Absorbance
(wavelength) Absorbance 100 % Absorbance 0 % Transmittance 0 %
Absorbance 100 % Transmittance Insert Photograph Spec-20
Sample-holder Meter Zero adjust and power control Wavelength scale
Wavelength control Light control Slide 4 Schematic representation
of a spectrophotometer Detector Sample-holder Meter Zero adjust and
power control Wavelength scale Wavelength control Light control
Monochromator Light Source (1) Sample cell (3) (2) (4) (5) IoIo I
Meter A spectrophotometer is an instrument that measures the
fraction (I/I o ) of an incident beam of light (I o ) which is
transmitted (I) by a sample at a particular wavelength. For a given
substance, the amount of light absorbed depends on: a) the
concentration; b) the cell or path length; c) the wavelength of
light; and d) the solvent. Slide 5 1.5 1.2 0.9 0.6 0.3 0.0
300400500600700800 Wavelength (nm) Absorbance Absorbance of
Chlorophyll 10 26 10 24 10 22 10 20 10 18 10 16 10 14 10 10 8 10 6
10 4 10 2 1 10 -8 10 -6 10 -4 10 -2 110 2 10 4 10 6 10 810 10 12 10
14 10 16 Frequency (Hz) Wavelength (nm) cosmic rays gamma rays
x-raysultra- violet infra- red radio (microwave) radartele- vision
radiopower transmission VioletBlueGreen YellowOrangeRed UV Near
Infrared 400 nm 500 nm 600 nm 700 nm Slide 6 Kelter, Carr, Scott,,
Chemistry: A World of Choices 1999, page 480 Amount absorbed 663 nm
Wavelength (nm) 400 500600700 Slide 7 Calibration Curve
Concentration Absorbance 100 % Absorbance 0 % Transmittance 0 %
Absorbance 100 % Transmittance out of linear range (too
concentrated) x 2 (fixed wavelength) ? Dilute sample with water
50:50. Run sample, read concentration. Slide 8 Dilution of
Solutions Keys Dilution of Solutions
http://www.unit5.org/chemistry/Solutions.html
