GCSE Chemistry Watch

CemXx732
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Can someone explain how paper chromatography separates substance?
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ChemistryWebsite
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Start by letting us know your understanding of it.
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CemXx732
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(Original post by TutorsChemistry)
Start by letting us know your understanding of it.
We only did this for about 10 minutes in lesson and have some understanding of how it works but I don’t know how to word it
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username3718594
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Substances in a mixture have different solubilities and attractions to the chromatography paper. Those substances which are more soluble and less attracted to the paper will move higher up the paper. Every substance has a different solubility and attraction to the paper, and this means that the substances can be separated by chromatography.
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amaraub
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(Original post by CemXx732)
We only did this for about 10 minutes in lesson and have some understanding of how it works but I don’t know how to word it
then watch a video on it.... google it... something....
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CemXx732
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(Original post by Anxiety Sucks)
Substances in a mixture have different solubilities and attractions to the chromatography paper. Those substances which are more soluble and less attracted to the paper will move higher up the paper. Every substance has a different solubility and attraction to the paper, and this means that the substances can be separated by chromatography.
Thank you so much!
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mojojojo101
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(Original post by Anxiety Sucks)
Substances in a mixture have different solubilities and attractions to the chromatography paper. Those substances which are more soluble and less attracted to the paper will move higher up the paper. Every substance has a different solubility and attraction to the paper, and this means that the substances can be separated by chromatography.
If they give you a mark for 'attraction to the paper' then you are very, very lucky because it is wrong.

The distance the dot travels depends on the substance's solubility in the solvent (mobile phase).
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CemXx732
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(Original post by mojojojo101)
If they give you a mark for 'attraction to the paper' then you are very, very lucky because it is wrong.

The distance the dot travels depends on the substance's solubility in the solvent (mobile phase).
Okay thanks!
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username3718594
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(Original post by mojojojo101)
If they give you a mark for 'attraction to the paper' then you are very, very lucky because it is wrong.

The distance the dot travels depends on the substance's solubility in the solvent (mobile phase).
It's on the AQA Chemistry GCSE specification, in the revision guide and on a couple of mark schemes I've seen, however incorrect it may be. This is only GCSE though; they're pretty basic in the information taught.
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expertguidance
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Objectives:
  • What is the use of chromatography to distinguish pure substances from impure.
  • Mechanism of paper cohmatography.
  • Interpretation of chromatograms.
  • Determination of Rf

Chromatograpy and its mechanism:
It involves a mobile phase and stationary phase.
Mobile phase moves through stationary phase having components of mixture under investigation.
Every component in mixture have different attraction towards stationery phase.
A substance having greater attraction between itself and mobile phase than itself and stationary phase cover greater distance in given time.
Substance having stronger force of attraction towards stationery phase will travel less distance.
How to distinguish:
In an organic solution chromatography ,we can tell its a mixture or pure substance.
In a mixture more than one spot formed on the chromatogram.
If only single spot formed,its a pure substance.
Example- Amino acid X from the mixture M has the strongest attraction to the solvent ,and amino acid Z has the strongest attraction to the paper.

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Identification using chromatography:
By comparison of spots on a chromatogram with other chromatograms which are obtained from known substances.
As in figure 3,mixture A still has one substance left unknown i.e in blue colour.
Attachment 720794720796
  • ts not practical to store chromatograms or their images on the computers.
  • To make valid comparisons all variables of an chromatograms be exactly same .
  • Its very effective to match a data collected on chromatogram to the database.
  • Data presented as Rf value -Retention factor
  • Ratio calculated by dividing the distance a spot travels up the paper by distance travelled by solvent.


For comparison to be valid you have to match the Rf value against the database.
Key points:
  • Paper chromatography is used to analyse unknown substances in solution.
  • To identify substances can be used against databases.
  • Retention factor- Ratio calculated by dividing the distance a spot travels up the paper by distance traveled by solvent.

I hope it helps. Please let me know if you need more information.

Thanks and Happy Revising
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