F324 - Chromatography Flashcards
How does Gas Chromatography separate compounds in a mixture?
By relative solubility.
Give two types of chromatography.
Thin Layer Chromatography (TLC) and Gas Ghromatography (GC or GLC).
How does Thin Layer Chromatography separate compounds in a mixture?
By adsorption
Give the equation to work out the Rf value.
Rf= distance travelled by component/distance travelled by solvent.
During TLC the speed of the compounds getting carried up the plate depends on two things. State them.
How soluble the compound is in the solvent; how much the compound and adsorbs onto the stationary phase.
Silica gel is present at the surface of a TLC plate. How does this slow down certain compounds in a mixture?
Certain compounds are adsorbed onto the plate more readily because they can form hydrogen bonds with the very polar OH groups at the surface of the silica gel.
Give the three types of intermolecular forces between molecules.
Van der Waal’s; permanent dipole; hydrogen bonding.
What is a relative solubility?
It is a measure of how soluble the substance is in the stationary phase compared to the mobile phase.
In Gas Chromatography what is the stationary phase and what is the mobile phase?
The stationary phase is an inert solid support and the mobile phase and is an inert gas
Define the term retention time.
The time taken for a compound to travel through the column to the detector from the point of injection.
State the three limitations with chromatography.
Analysis of similar compounds as they will often have similar retention times or Rf values; reference retention times are impossible when dealing with unknown substances; retention times are dependent on temperature.
How do chemists improve analytical techniques in chemistry?
By combining analytical techniques to make them more powerful when used together. For example combining mass spectroscopy and chromatography (GC-MS).
Define chromatogram
A visible record showing the result of separation of the different components of a mixture by chromatography
