A study about a separation technique Chromatography Lab A study about a separation technique

Chemistry Background Mixture – combo of substances which can be separated Solution – type of mixture #1 chlorophyll pigment #2 carotenoid pigment Pigment molecules in each – Are the solute molecules in the solution Liquid organic compound – Is the solvent molecules Solvents dissolve solutes Remember, molecules interact with each other – intermolecular forces

What’s involved? Phases of Chromatograpy: Mobile phase – a solvent compatible with the mixture’s solutes – moves the mixture for separation Stationary phase – material that holds the mixture and does the separating – sets the criteria used for molecule separation Discussion on the Analogy of a strainer when making a mixture of different size pasta noodles Discussion of gel electrophoresis

How does it separate?

Materials Needed: Two glass vials with lids per pair One bottle of developing solution and an eyedropper to share Two bottle of plant pigments: chlorophyll and carotenoid to share Vial of capillary tubes to apply on silica gel strip to share Pair does two chromatography separations: one does chlorophyll and one does carotenoid

Removing the Chromatograph Open the vial Look for the line that marks the wet and the dry area. Place it on the white paper. Mark the solvent front similar to the illustration. Mark origin. Id bands and label

Assignments Read AP Lab 4A and complete lab reading questions. Draw a table on the half sheet of white unlined paper with a ruler. This will be used to display band #, color and Rf value Be sure to think about how to position the table to accommodate for the chromatograph

Paper Chromatography

Are bands of the same color the same pigment? Explain

How does thin layer chromatography work? The stationary phase - silica gel Silica gel is a form of silicon dioxide (silica). The silicon atoms are joined via oxygen atoms in a giant covalent structure. However, at the surface of the silica gel, the silicon atoms are attached to -OH groups. So, at the surface of the silica gel you have Si-O-H bonds instead of Si-O-Si bonds. The diagram shows a small part of the silica surface. The surface of the silica gel is very polar and, because of the -OH groups, can form hydrogen bonds with suitable compounds around it as well as van der Waals dispersion forces and dipole-dipole attractions The other commonly used stationary phase is alumina - aluminium oxide. The aluminium atoms on the surface of this also have -OH groups attached. Anything we say about silica gel therefore applies equally to alumina.

Data Organization Band # Color Rf Value Solvent front 1 2 3 4 5 6 7 8 Table drawn below chromatograph origin Chromatograph taped to the half sheet of white paper

How To Quantify Data with the Rf Value Watch the video to understand how to calculate the Rf value. Click on the above link.

Calculating Rf

Be ready for an evaluation Lab Assignment: A Data Sheet which has the following: A title for the chromatography An annotated chromatograph – origin, solvent front, labeled bands A complete data table with Band#, color, Rf value Name, Period and Date in an appropriate area on paper Review background, procedure and application info Be ready for an evaluation Even if the bands on the chromatograph share the same color to the naked eye, why are they not considered the same compound? Explain.

Further Your Understanding Various Uses for Thin Layer Chromatography