Paper chromatography Flashcards
What is chromatography ?
It is an analytical method used to separate the substance in a mixture. You can then use it to identify the substances.
There are different type of chromatography, but they all have two phases. What are these phases?
A mobile phase
A stationary phase
What is the movie phases of chromatography?
Where the molecules can move. This is always a liquid or a gas.
What is the stationary phase of chromatography?
Where the molecules can’t move. This can be a solid or a really thick liquid.
During a chromatography experiment, the substance in the sample constantly move between the monkey and stationary phases . What is formed between the two phases ?
An equilibrium
The mobile phase moved through the stationary phase and whatever is dissolved in the mobile phase moves with it. What does how quickly a chemical moves depend on ?
How quickly a chemical moves depends on how it’s distributed between the two phases - weather it spends more time in the mobile phases or stationary.
What happens to the chemicals that spend more time in the mobile phase than the stationary ?
They will move further.
What happens to the components during a chromatography cycle ?
The components of a mixture in a mixture will normally separate throught the stationary phase, so long as the components spend different amounts of time in the mobile phase.
What happens with the number of dots during paper chromatography ?
The number of dots math change in different solvents as the distribution of the chemical will change forming in the solvent. A pure substance will only ever form one spot in any solvent as there is only one substance in the sample.
During paper chromatography what is the stationary phase ?
The chromatography paper ( often filter paper )
During paper chromatography what is the mobile phase ?
The solvent ( e.g. ethanol or water )
The amount of time the molecules spend in each phase depends on what two things ?
How solvable they are in the
solvent.
How attracted they are to the paper.
What type of molecules will spend more time in the mobile phases - so they will be carried further up the paper ?
Molecules with a higher solubility in the solvent, which are less attracted to the paper.
What is the result of chromatography analysis called ?
Chromatography
What is an Rf value ?
The Rf value is the ration between the distance travelled by the dissolved substance ( the solute ) and the distance travelled by the solvent.
The further through the stationary phases a substance pmoves, the larger the Rf value. You can calculate Rf value using the formula:
Rf = distance travelled by substance (B) / distance travelled by solvent (A)
Why is chromatography carried out ?
To see if a certain substance is present in a mixture. To do this, you rub a pure sample of that substance alongside the unknown mixture. If the Rf values of the reference and one of the spots in the mixture match, the substance may be present ( although you haven’t yet proved they’re the same)
What does the Rf value depend ?
The Rf value is dependent on the solvent - if you change the solvent the Rf value for a substance will change.
What does it mean when the Rf value of the reference the Rf value of one of the spots in the mixture in all the solvents.
The it is likely the reference compound is present in the mixture.
What does it mean if the spots in the mixture and the spot in the reference only have the same Rf value in some of the solvent?
Then the reference compound isn’t present in the mixture.
