Dilution and Spectroscopy Lab Lab Word Document Lab Word Document

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

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 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

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 holder cover Amplifier control knob Light control knob Wavelength control knob

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.

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

Wavelength (nm) Absorbance Absorbance of Chlorophyll 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

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

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.

Dilution of Solutions Keys Dilution of Solutions