Paper Chromatogtaphy Flashcards
Chromotography
Analytical method used to separate the substances in the mixture. Used to identify substances.
A mobile phase
Moves through the stationary phase, carrying components of the mixture under investigation. This is always a liquid or a gas(solvent, water or ethanol)
A stationary phase
Where the molecules cannot move. This can be solid or thick liquid(chromatography paper)
Rf value
Rf=distance travelled by substance/distance travelled by solvent
Pure element
Contains only one substance, with no other substances mixed in.
Mixture
Is made up of two or more elements or compounds which are not chemically combined together.
Compounds properties
- fixed composition(the ratio of elements presented)
- need a chemical reaction to separate
- chemical bonds between atoms of different elements
Mixtures properties
- no fixed composition
- can be separated without chemical reaction
- no chemical bonds between atoms
How to separate mixture?
- filtration
- crystalisation
- distillation
- chromotography
Filtration
Used to separate substances that are insoluble in a particular solvent from those that are soluble.
Crystallisation
Used separate soluble solid from a solvent by evaporating the water.
Distillation
Separation of a liquid from a mixture by evaporation followed by condensation.
Uses of distillation
-to obtain freshwater from saltwater
-
Miscible liquids
Liquids that are dissolved in each other.
Immiscible liquids
Form separate layers when mixed.
Miscible liquids have…
a different boiling point, so this property is used to distil off and collect liquid with the lowest boiling point first.
Why is it hard to obtain a pure liquid using simple distillation?
Vapur is given off from liquids before they actually reach their boiling point. Especially in the case where liquids have a similar boiling point.
What can be used to increase the purity of destination?
Fractional column.
A substance that travelled the most has…
the strongest attraction to the solvent.
A substance that travelled the least has…
the strongest attraction to the paper.
When comparing rf value of a substance to a database…
it is important to make sure that solvent and temperature used are same as that in a database.
