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CHM lab 9
| Question | Answer |
|---|---|
| what does TLC stand for? | thin layer chromatography |
| what is the adsorbent used on TLC plates? | silica gel |
| why do compounds "stick" to silica gel? | silica has Si-OH groups that hydrogen bond with polar molecules |
| what is the eluent? | the solvent used to carry compounds up the plate |
| what 2 solvents are used in this lab? | ethyl acetate and hexanes |
| how does polarity influence movement on TLC? | more polar- sticks to silica-moves less, less polar- sticks less-moves more |
| what is an Rf value? | distance traveled by compound divided by distance traveled by solvent front |
| can 2 different compounds have the same Rf? | yes |
| why must the pencil line be above the solvent line? | the samples dissolve into the solvent instead of traveling up the plate |
| why must you spot with a pencil and not a pen? | ink contains organic molecules that run on the plate |
| why must TLC spots be small? | large spots smear and overlap |
| why must the TLC chamber stay covered? | to saturate the atmosphere with solvent vapor |
| why does ibuprofen require a full micropipette of solution? | its less soluble |
| what does seeing 2 spots for the unknown mean? | the tablet contains more than one active ingredient |
| what is the purpose of testing known standards first? | to determine Rf values and identify components int he unknown |
| if a compound barely moves up the plate, what does this say about its polarity? | its very polar |
| if the solvent mixture is too polar, what happens? | all compounds run too high |
| if the solvent mixture is too nonpolar, what happens? | compounds barely move |
Created by:
Riley06
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