Required practicals 🥼🧪
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What does paper chromatography allow us to do?
• paper chromatography, allows us to separate different substances based on their different solubilities.
Describe a method you would do to carry out paper chromatography [5] Hint: draw, pipette, place, solvent, dry
• draw a pencil line across chromatography paper (about 1 cm above the bottom) • use a pipette, or capillary tube, to add small spots of each ink (A,B, C and D) to the line on the paper, as well as unknown ink (U) (equally spread across the paper) • place the paper into a container with a suitable solvent (e.g. water) in the bottom - making sure the pencil line is above the water line • and allow the solvent to move through the paper, but remove the chromatogram before it reaches the top • then allow the chromatogram to dry, and measure the distance travelled by each spot and by the solvent
With chromatography, is there a limit to how many substances we can test?
• no, with chromatography this can be done with several colours; there has to be enough space on the paper.
What is the stationary phase in paper chromotography ?
• In paper chromatography, the stationary stage is called the paper- because it doesn’t move.
What is the mobile phase in paper chromatography?
• In paper chromatography, the mobile phase is the solvent- since it does move.
In chromatography, what’s the difference between the stationary 🆚️ mobile phase?
• the stationary stage is called the paper- because it doesn’t move • ; the mobile phase is the solvent- since it does move.
In paper chromatography, how do we know if a colour is a single substance?
• there will be only one spot
How do we know in paper chromatography, that a colour is a mixture of two different substances?
• the colour will separate into two different spots.
Why does paper chromatography work? [3]
• paper chromatography works, because each chemical in the mixture will be attracted to the stationary phase (the paper), to a different extent. • and chemicals that are strongly attracted to the stationary phase (the paper) will not move very far. • chemicals that are weakly attracted, will move further up the paper.
What will a pure chemcial produce, 🆚 chemicals in a mixture?
• a pure chemical produces singles spot in all solvents • ; a chemical in a mixture may separate into different spots, based on the solvent.
In paper chromatography, why do we draw our starting line in pencil instead of pen ? Hint: ⬆️
• We draw our starting line in pencil, since if it was in pen: the pen ink would move up the paper with the solvent.
What is the calculation for Rf value ?
Rf value= distance moved by substance ➗ distance moved by solvent