1. Serial Dilution Activity Using a pipet Simulated Acid: Red = nitric acid Yellow = sulfuric acid Blue = hydrochloric acid

2. Spec-20 Instrument Sample holder cover Amplifier control knob Light control knob Wavelength control knob

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

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.

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

6. Kelter, Carr, Scott,, Chemistry: A World of Choices  1999, page 480 Amount absorbed 663 nm Wavelength (nm) 400 500600700

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.

8. Dilution of Solutions Keys Dilution of Solutions http://www.unit5.org/chemistry/Solutions.html