C12.2 Analysing chromatograms
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What is the mobile phase?
It moves through the stationary phase carrying the components of the mixture under investigation with it The mobile phase is the solvent chosen
What is stationary phase?
Can be thought of as the paper
How can a substance be carried a greater distance in a given time?
A substance with stronger forces of attraction between itself and the mobile phase than between itself and the stationary will be carried a greater distance in a given time
How can a substance be carried in a short distance in a given time?
If the substance has a stronger force of attraction to the stationary phase will not travel as far in the same time
How can chromatography tell you if the substance is a simple compound or substance?
If the unknown sample is a mixture of compounds there will probably be more than one spot formed on the chromatogram On the other hand a single spot indicates the possibility of a pure substance
What is a chromatograph?
A visible record (such as a graph) showing the result of separating the components of a mixture by chromatography.
What is the R(f) factor (Retention factor)?
This is a ratio between the distance moved by the substance and the distance moved by the solvent
What is the formula to calculate the R(f) value?
Distance moved by the substance / distance moved by solvent
How can you ensure your results be valid when calculating the R(f) value?
You have to ensure that the solvent and the temperature used are the same as those quoted in the database
What is the purpose of the R(f) value?
Rf values can be used to identify unknown chemicals if they can be compared to a range of reference substances. The Rf value for a particular substance is always the same if the same solvent and stationary phase are used. This is far more accurate than storing the data on the computer and comparing it to every single colour