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Dilution and Spectroscopy Lab

Dilution and Spectroscopy Lab. Lab Word Document. Dilution Background. Acids and bases usually come in concentrated form, as “concentrates,” but they are rarely used in this form.

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Dilution and Spectroscopy Lab

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  1. Dilution and Spectroscopy Lab Lab Word Document

  2. 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

  3. 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

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

  5. 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.

  6. 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

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

  8. Meter Wavelength control Wavelength scale Sample-holder Light control Zero adjust and power control Schematic representation of a spectrophotometer I Io Monochromator Detector Meter Light Source (1) Sample cell (3) (2) (5) (4) 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.

  9. Meter Wavelength control Wavelength scale Sample-holder Light control Zero adjust and power control Insert Photograph Spec-20 Spec-20 Absorbance 100 % Absorbance 0 % Transmittance Absorbance 0 % Absorbance 100 % Transmittance l (wavelength)

  10. Frequency (Hz) 1 102 106 104 1010 108 1022 1020 1018 1016 1014 1026 1024 infra- red radio (microwave) radar tele- vision radio power transmission gamma rays x-rays ultra- violet cosmic rays 1016 1012 1014 106 108 1010 10-4 10-2 1 102 104 10-8 10-6 Wavelength (nm) Near Infrared UV Yellow Orange Red Violet Blue Green 700 nm 600 nm 500 nm 400 nm Absorbance of Chlorophyll 1.5 1.2 0.9 Absorbance 0.6 0.3 0.0 300 400 500 600 700 800 Wavelength (nm)

  11. Amount absorbed 663 nm 400 500 600 700 Wavelength (nm) Kelter, Carr, Scott, , Chemistry: A World of Choices1999, page 480

  12. 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 50:50. Run sample, read concentration.

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

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