To separate a mixture of indicators or coloured substances using paper chromatography Flashcards
What is meant by the term chromatography?
Chromatography is a separation technique in which a mobile phase carrying a mixture moves in contact with a selectively adsorbent stationary phase
Name the scientist who invented the technique of chromatography
Mikhail Tswett
What is the principle on which all chromatographic separation techniques are based?
Different components of a mixture are attracted to different extents to the mobile phase as compared to the stationary phase
In the experiment undertaken by you, what is the mobile phase and what is the stationary phase?
Type - Paper Chromatography
Mobile - Ink solution
Stationary - Water on paper
Why should chromatography paper be handled as little as possible with bare hands?
To avoid oils from the hands contaminating the results
State which colour inks may be good for separating. Explain your answer
Black and brown ink are good for separating as they are usually made by mixing a number of colours
What do the letters TLC represent?
Thin Layer chromatography
What is the process of passing a solvent through a column called?
Elution
Describe how a student could have used chromatography to separate a mixture of indicators
- add solvent to bottom of tank and cover
- allow stand for few hours to allow tank to become saturated with solvent vapour
- make line with pencil near top of chromatography and another line about 3cm from bottom [eluent]
- place small spot of mixture of indicators at line near bottom using capillary tube
- place chromatogram in tank and run it, until solvent moves up and reaches line near top of paper, separating the components
Explain why different components of the mixture travel different distances along the paper or along the thin-layer or through the column in a given time
Different adsorbance on mobile and stationary phases
Why are two lines drawn on the paper?
One line is needed to indicate where the samples start from, and the other to indicate the distance travelled by the solvent front, which enables the Rf values to be calculated
When two substances are found to have two different
Rf values in an experiment carried
out under the same conditions, what does this mean?
The two substances are not identical.
When is it possible to separate two components of a mixture using paper chromatography?
When one of the components is attracted to significantly different extents by the stationary
phase and/or the mobile phase
What is the rF of a substance and whats the formula
Dsitance moved by substance
Distance travelled by component / distance travelled by solvent front
Give a use
Separating dyes from fibres
