C5 Chromatography Flashcards
What is chromatography?
An analytical method used to separate the substances in a mixture.
Why may we need to separating the substances in a mixture?
To identify the substances.
There are different types of chromatography, but they all have two phases. Name the two phases.
A mobile phase.
A stationary phase.
What happens in the mobile phase of chromatography?
Where the particles of the phase can move.
What state is the mobile phase?
Liquid or gas
What happens in the stationary phase of chromatography?
Where the particles of the phase can’t move.
What state is the stationary phase?
This can be solid or a very thick liquid.
During a chromatography experiment, the substances in the sample constantly move between the mobile and the stationary phases. What is formed between the two phases?
An equilibrium.
Different chemicals will have different distributions between the same phase. What does this mean?
They’ll spend different amounts of time dissolved in the mobile phase or attracted to the stationary phase.
Complete the sentence
The mobile phase moves through the stationary phase, and anything ……….. in the mobile phase moves with it.
Dissolved
How does the amount of time a chemical spends in the mobile phase affect the stationary phase?
The more time a chemical spends in the mobile phase, the further through the stationary phase it’ll move.
What will a chromatogram of a chemical with different distributions show?
The different distributions will separate into different spots on the chromatogram.
What affect would a different solvent have ?
The number of spots may change in a different solvent as the distribution of the chemical will change depending on the solvent.
What will a chromatogram of a pure substance show? Why?
One spot in any solvent, as there is only one substance in the solution.
If a chromatogram has more than one spot, what can we say about the substance?
It is a mixture.
One type of chromatography is paper chromatography. What are the mobile and stationary phases in this method?
Chromatography paper is the stationary phase (often filter paper)
Solvent is the mobile phase.
What does the amount of time the molecules spend in each phase depend on?
How soluble the molecules are and how attracted they are to the paper.
Which phase do molecules with higher solubility in the solvent spend more time in? Why?
Mobile phase
They are less attracted to the paper, so spend more time in the mobile phase and are carried further up the paper.
See p 60 for chromatography practical.
.
Explain how paper chromatography separates mixtures. (4 marks)
During paper chromatography, the molecules of each chemical in the sample move between the stationary phase and the mobile phases. (1 mark)
The mobile phase moves through the stationary phase over the course of the experiment, and anything that’s dissolved in it will move with it (1 mark)
The distance a compound moves through the stationary phase depends on how long it spends dissolved in the mobile phase compared to on the stationary phase (1 mark).
Since different compounds will interact differently with the mobile phase and the stationary phase, they’ll move different amounts through the stationary phase, and so be separated from each other (1 mark).
