15E.1 Flashcards
what is chromatography used for
- to separate the mixture into components
- to identify the components of the mixture by considering how far they have travelled up the paper
- to check if an organic compound is pure or not by following the two things above
what do you need to set up a chromatography experiment
- a container (made out of glass) it could be a beaker or a rectangular tank with a lid
- paper. we can use filter paper or kitchen towel but using a chromatography paper gives better results. also we need a method to support the paper in the container
- solvent. water can work, but in most situations it is a a mixture of organic compounds, that are chosen to fit the characteristics of the of the components of the mixture
why do we use a lid in chromatography
the prevent the evaporation of the solvent
how do you carry out a chromatography
the mixture is spotted onto the paper a short distance away from the edge ( often spots of known substances are spotted separately at the same level as the mixture ) then a small amount of the chosen solvent is added to the container, and the paper is inserted and suitably supported, then the lid is replaced and the apparatus is left till the solvent front reaches almost the end of the paper, the paper is removed and the solvent front is marked and then the paper will be left to dry
what is the chromatogram
the dried paper used in chromatography
usually in the chromatogram the spots are
elongated and hard to find there centers
chromatography depends on the use of
- the stationary phase
- the mobile phase
what is the stationary phase in chromatography
the liquid or solid that does not move
what is the mobile phase in chromatography
the liquid that moves through the stationary phase and transports the components
components who don’t travel very far up the paper are
strongly attracted to the stationary phase but weekly attracted to the mobile phase
components who travel very far up the paper are
strongly attracted to the mobile phase and weekly attracted to the stationary phase
in paper chromatography the mobile phase is
the solvent
in paper chromatography the stationary phase is
the water that is trapped in the fibers of the chromatography paper
how do we get coloured components when doing paper chromatography on organic substances
- using ultraviolet radiation
- by spraying with a chemical regent that will react with components to from a coloured product
what is the difference between thin-layer chromatography (TLC) and paper chromatography
in TLC is the same as paper chromatography just the paper is replaced by a sheet of glass or plastic coated with a thin layer of solid such as silica or alumina
how do you calculate the Rf (retardation factor) value
distance travelled by component / distance travelled by solvent (no units since ratio)
each component in chromatography will have
its own Rf value
the Rf value depends on
solvent used and other factors (the paper (stationary phase) )
can we always use Rf to identify components
yes from the table, but in different solvents components will have different Rf
the distance moved by the component is
the distance measured between the baseline and center of the component
the distance moved by the solvent is
the distance measured between the baseline and the solvent front
why do we put known substances beside the mixture
to see if the mixture has any of those substances
how does column chromatography work
alumina or silica are packed into a tube ( a burette is suitable) and are soaked with the solvent, the mixture is then places on top of the silica/alumina and then more solvent is added on top , then the tap is opened and the solvent will drip through the tip and the mixture begins to move down the top and sperate, then more solvent is added at the top of the burette and eventually on component leaves the column and is collected in a container (we can do the same thing for all the other components)
in column chromatography the stationary point is
the alumina or silica
