Chromatography Flashcards
How do you set up the chromatography experiment?
- Get a rectangular (or not) piece of filter paper
- Draw a straight line using a pencil 3cm above the bottom of the filter paper (this is a baseline)
- Add you sample off ink as a dot on the base line
- Find a beaker and fill it with a shallow amount of solvent and put the filter paper in the beaker so that so that it’ll touch the bottom of the paper under the baseline but won’t submerge the baseline/spot of ink
- When the solvent has nearly reached the top of the paper, take the paper out of the beaker and leave it to dry
What is the end result of the experiment called?
A Chromatogram
What can you also do to be careful?
Place a lid on top to stop the solvent from evaporating.
Why do you use pencil for the base line?
Because pencil marks are insoluble and won’t dissolve in the solvent
What will happen?
The solvent will move up the paper carrying the ink with it. Each different dye that makes up the ink will move up the paper at a different rate and therfore seperate, forming a spot in a different place.
What will happen to chemicals that aren’t soluble?
If they’re insoluble in the solvent used, they’ll stay on the base line and not move.
What is the mobile phase?
It’s the substance that the molecules can move in. Always a liquid/gas. In chromatography this is the solvent.
What is the stationary phase?
The substance the molecules can’t move in. Usually a solid or a really thick liquid. In this experiment it’s be the paper
The different chemicals will constantly change between the mobile and stationary phase
. they’ll move a little bit and then bind to the paper over and over again
What will determine the rate the chemicals move up the paper?
How fast they move between the mobile and stationary phases will determine how fast they move up the paper.
Which phase do more soluble chemicals or chemicals that er less attracted to the paper spend time in?
the mobile phase so they move up the paper faster.
Which phase do less soluble chemicals or chemicals that are more attracted to the paper spend time in?
The stationary phase so they travel up the paper slower
What other factor affects how far the chemicals travel?
How long we leave the paper
What will happen if the substance is pure?
It will only ever form one spot in any solvent
The distance a chemical travels is dependant on it’s properties.
If we want to identify a substance or chemical we can measure how far each substance moves and compare the values to a data book to identify the type of chemical.
What is the Rf value?
The ratio between the distance travelled by the dissolved substance and the distance travelled by the solvent.
How do you calculate the Rf value?
Distance travelled by the substance (B) ÷ distance travelled by the solvent
What is B
The distance from the baseline to the centre of the spot.
The further through the stationary phase the substance moves, the higher the Rf value.
The solvent can also affect the Rf value.
How can the solvent affect the Rf value?
It can change the mobile or stationary phase
What can chromatography be used for?
separate mixtures and give information to help identify substances
