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5.6Chemistry 02. Properties Of Materials

Describe how paper chromatography can be used to separate and… — Cambridge Checkpoint Science 0893 Revision Notes & Topical Questions

5 min read 9 parts Lesson 6 of 9 1 quiz

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Lesson summary

5.6 Paper chromatography — CHECKPOINT - Lower Secondary Science 0893 notes: Describe how paper chromatography separates and identifies the coloured substances in a mixture.Paper chromatography — a technique that separates the different coloured substances dissolved in a mixture s…

  • Chromatogram
  • Pure substance or mixture
  • Solubility
  • Pencil line
  • Spot above the solvent
  • Removing early

Section 1 of 9Purpose of chromatography

Purpose of chromatography
Paper chromatography
  • Paper chromatography a technique that separates the different coloured substances dissolved in a mixture such as ink.
Chromatogram
  • Chromatogram the paper with the separated colours on it after the experiment.
Pure substance or mixture
  • Pure substance or mixture a pure substance gives one spot and a mixture gives two or more spots.

Section 2 of 9Why the colours separate

Solvent
  • Solvent the solvent, such as water, soaks up the paper and dissolves the coloured substances.
Carrying
  • Carrying the moving solvent carries the substances up the paper.
Solubility
  • Solubility more soluble substances are carried further up the paper.
  • So different substances stop at different heights and separate.

Section 3 of 9Method

1
Draw a pencil line about 1 cm from the bottom of a strip of chromatography paper.
2
Place a small spot of ink on the pencil line and let it dry.
3
Add a little more ink on the same spot and let it dry.
4
Pour about 2 cm depth of solvent into a beaker.
5
Hang the paper so that the bottom edge touches the solvent and the ink spot stays above the solvent level.
6
Watch the solvent move up the paper.
7
Remove the paper before the solvent reaches the top, and mark the solvent front.
8
Allow the chromatogram to dry.

Section 4 of 9Reasons for the method

Pencil line
  • Pencil line pencil does not dissolve in the solvent, but ink would run.
Spot above the solvent
  • Spot above the solvent if the spot is under the solvent the ink dissolves into the beaker.
Removing early
  • Removing early the solvent front must not reach the top so the distances can be compared.
Small spot
  • Small spot a small spot gives clear, separate spots.

Section 5 of 9Choosing the solvent

Water
  • Water used for inks that are soluble in water.
Ethanol or alcohol
  • Ethanol or alcohol used for substances that are not soluble in water, such as permanent marker ink and plant pigments.

Section 6 of 9Reading a chromatogram

Number of spots
  • Number of spots each spot is one substance.
Matching
  • Matching spots from different samples at the same height are the same substance.
Most soluble
  • Most soluble the substance that travels furthest.
Least soluble
  • Least soluble the substance that travels the shortest distance.

Section 7 of 9Uses

Uses
Scientists identify the dyes in food, hair dye and ink.
Chromatograms of a sample are compared with permitted substances.

Section 8 of 9Key terms

TermMeaning
ChromatographyA method of separating dissolved substances using a solvent moving through paper.
ChromatogramThe result on the paper showing the separated substances.
Solvent frontThe highest point the solvent reaches on the paper.
SolubleAble to dissolve in a solvent.
Pure substanceA single substance that gives one spot.

Section 9 of 9Exam technique

1
Chromatography separates by size alone — substances separate by their solubility in the solvent.
2
The ink spot should be below the water — it must be above the level of the solvent.
3
Pencil and ink behave the same — pencil does not dissolve.
4
A single spot means a mixture — a single spot means one pure substance.

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