U3-5 - Chemical Analysis
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State two factors which influence Rf value/retention time.
Polarity Molecular mass Accept molecular size
What is the relationship between molecular mass and retention time? Also applies for molecular size
As molecular mass increases, retention time increases. Heavier molecules travel more slowly = take longer to reach detector
How can a gas chromatogram indicate the quantity of substance present?
Area under each peak corresponds to quantity Bigger area = more of that substance present
Mobile phase
Solvent (TLC/paper) or gas (gas chromatography)
Stationary phase
Paper/TLC plate OR high b.p. liquid (gas chromatography)
If the mobile phase is ethanol, what type of substance will travel faster: polar or non-polar?
Polar Ethanol is polar
If the mobile phase is helium, what type of substance will travel faster: polar or non-polar?
Non-polar Helium is non-polar