1. Dilution and Spectroscopy Lab Lab Word Document 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: M 1 V 1 = M 2 V 2 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. Pipet Instructions 1.Press the A button and squeeze the bulb to suck air out 2.Place the pipet into the solution 3.Press the S button to suck the liquid into the pipet 4.Take the pipet out of the solution and place it into the next cuvette 5.Press the E button to empty the liquid into the new cuvette A E S

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 Sample holder cover Amplifier control knob Light control knob Wavelength control knob

8. 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 of an incident beam of light which is transmitted or absorbed by a sample at a particular wavelength.

9. 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

10. 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

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

12. 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.

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