chromatography Flashcards
what is chromatography used for?
to separate mixtures and can give information to help identify substances
stationary phase
paper
mobile phase
solvent
what does the amount of time molecules spend in each phase depend on?
-how soluble they are in the solvent
-how attracted they are to the paper
Rf equation
distance moved by substance/
distance moved by solvent
what does separation depend on?
the distribution of substances between the phases
how can you identify compounds and why?
by calculating the Rf value as different compounds have different Rf values in different solvents
how can you tell the difference between a mixture and a pure substance from chromatography?
compounds in a mixture may separate into different spots depending on the solvent but a pure compound will produce a single spot in all solvents
what is the result of a chromatography analysis called?
a chromatogram
why should you use pencil in chromatography?
it is insoluble and won’t dissolve in the solvent and affect the results
chromatography
used to separate the substances in a mixture based on how the components interact with a mobile and stationary phase
method
- Use a ruler to draw a horizontal pencil line 2 cm from the bottom of the chromatography paper.
- Put a small spot of each of the substances along the pencil line.
- Pour 1cm water into the beaker.
- Place the paper into the beaker, ensuring the solvent is below the start line.
- Wait for the solvent to travel at up the paper.
- Remove the paper and draw another pencil line where the solvent has stopped.
- Measure the distance in between the two pencil lines.
- Calculate the Rf value using distance moved by substance/solvent
why must the start line be above the solvent level?
so the solvent doesn’t dissolve the substance before it can move up the paper
