Chromatography Flashcards
(17 cards)
What is chromatography?
A separation technique used to separate out a mixture and find what is contained within the sample.
Why do dyes separate during chromatography?
Because dyes move at different speeds depending on their solubility and affinity to the stationary or mobile phase.
What are the stationary and mobile phases in paper chromatography?
Stationary phase = paper. Mobile phase = solvent.
What is ninhydrin used for in chromatography?
It reveals colourless amino acids, making them visible after separation.
Why is the starting line drawn in pencil, not pen?
Pencil is insoluble in water, avoiding contamination and ensuring accurate results.
Why must the solvent be below the sample spots?
So it travels up the paper and carries the dyes with it instead of dissolving them in the beaker.
Why do some dyes travel further than others?
Because they are more soluble in the solvent and more attracted to the mobile phase.
What does it mean if a dye is more attracted to the stationary phase?
It will stay closer to the baseline and move less.
What is the Retention Factor (Rf)?
Rf = Distance moved by the substance ÷ Distance moved by the solvent.
What does a higher Rf value mean?
Greater solubility in the solvent.
Why is Rf measured to the centre of the spot?
It’s the most concentrated and accurate point of the substance.
How do you obtain a dry sample from chromatography?
1) Dissolve in a suitable solvent. 2) Evaporate the solvent. 3) Dry the substance.
What factors affect how far each spot travels?
Solubility, affinity for the phases, polarity, and temperature.
What are polar substances like in chromatography?
Attracted to the polar stationary phase (paper), dissolve in polar solvents, and move slowly.
What are non-polar substances like in chromatography?
Attracted to the non-polar mobile phase, dissolve in non-polar solvents, and move faster.
Why do non-polar substances attract each other?
Due to London dispersion forces (temporary dipoles), which are weak but allow solubility in non-polar solvents.
How does temperature affect chromatography?
Higher temperatures increase solubility by providing more energy to break bonds and help particles dissolve and move faster.
