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Identifying the components of a mixture

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1 Identifying the components of a mixture
Paper Chromatography Identifying the components of a mixture

2 Chromatography Chromatography is a method for separating mixtures into their components based on physical and/or chemical properties of the components. Developed around 1903 by Russian Mikhail Semenovich Tswett in which he separated plant pigments on “diatomaceous earth” with alcohol

3 Uses for Chromatography
Chromatography can be used to: Qualitatively analyze the components of a mixture Qualitatively identify the components of a mixture using known compounds Quantitatively determine the amount of a component in a mixture using standard samples Purify individual components by separating them from the other compounds in a mixture

4 The Basics Mixture is placed on stationary phase
Mobile phase passes over the stationary phase Mobile phase dissolves the components Mobile phase carries the individual components a certain distance through the stationary phase, depending on their attraction to both of the phases

5 Rf ratio of spot distance to solvent front distance
Chromatographed Spot Rf ratio of spot distance to solvent front distance Put the spotted paper in a developing tank Origin line Solvent

6 Principles of Paper Chromatography
Capillary Action – the movement of liquid within the spaces of a porous material due to the forces of adhesion, cohesion, and surface tension. The liquid is able to move up the filter paper because its attraction to itself is stronger than the force of gravity. Solubility – the degree to which a material (solute) dissolves into a solvent. Solutes dissolve into solvents that have similar properties. This allows different solutes to be separated by different combinations of solvents. Separation of components depends on both their solubility in the mobile phase and their differential affinity to the mobile phase and the stationary phase.

7 Investigation: What Dyes are in the M&Ms and Food Colors?

8 Preparing the Chromatography Paper
Obtain an 7 x 8 cm of chromatography paper With a pencil (why?), draw an origin line 1 cm above the bottom edge of the strip. Near the top, ID the chromatogram Mark the origin line with a lane mark each cm. No lane can be closer than about 1 cm from the edge

9 Preparing the Chromatography Paper
ID each lane and record what each lane is spotted with Place a spot from each solution on the origin More than one strip may be required to analyze all of the solutions

10 Developing the Chromatograms
Add chromatographic solvent to a sufficiently large beaker to a depth of less than 1 cm Place the spotted paper in the beaker carefully Ensure the solution does not go above the origin line Develop the chromatogram until the solvent front is about 2 cm from the top of the paper

11 Developing the Chromatograms
Remove the chromatogram and place on a paper towel, trace the solvent front with pencil, and let the chromatogram dry in the oven for a few minutes. After the chromatogram is dry, calculate the retention factors, Rf, and tabulate the values Determine the dye content of each of the “unknowns”

12 Considerations Small spots are generally better but harder to see after developing UV lamps, if available can (sun)burn your eyes but UV is stopped by the plastic of your goggles UV lamps are low power but extended exposure can cause a mild (sun)burn Don’t eat the M&Ms – they’ve been in the lab awhile

13 Writing Procedure Proposals
Clearly state your experimental methods and how those procedures will yield solutions to the problems addressed in the investigation. State what data you plan to collect and how you will analyze the data. Include proposed data tables. State all the materials you plan to use including, if possible, concentrations and quantities. Describe the safety hazards associated with your analysis and appropriate precautions you will take to avoid personal injury. Each team member must sign and date the procedure proposal before turning it in.

14 Author List This investigation, Author 3: Introduction and Conclusion
1: Discussion 2: Data/Results and Experimental B: Introduction, Conclusion, Data/Results A: Discussion and Experimental


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