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Criteria of Purity







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Description:
Criteria of Purity . a) Describe paper chromatography and interpret chromatograms b) Describe how chromatography techniques can be applied to colourless substances. c) Identify substances and test their purity by melting point and boiling point determination and by paper chromatography.
Criteria of Purity

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Slide 1

Criteria of Purity

a) Describe paper chromatography and interpret chromatograms

b) Describe how chromatography techniques can be applied to colourless substances.

c) Identify substances and test their purity by melting point and boiling point determination and by paper chromatography.

d)Explain the importance of purity in substances in everyday life. Eg. in foodstuffs and drugs.

Slide 2

Chromatography

  • method of separating and identifying mixtures;

  • used to separate the solutes in a mixture

  • Eg. to identify artificial dyes in food

     can be used to identify very tiny amounts of substances

Slide 3

Chromatography

Slide 4

Chromatography

Slide 5

Chromatography

  • principle involved depends upon the different solubilities of the substances in the mixture in the solvent used – the most soluble solute will be carried quickly up the paper with the solvent while the least soluble solute will be left behind.

  • Steps involved

Slide 6

Chromatography

  • a dye strongly adsorbed onto paper, and not very soluble in solvent will be left behind

  • a dye weakly adsorbed onto paper, and very soluble in solvent will be carried furthest

  • simulation

Slide 7

Chromatography

solvent front

ensure that the spots are above the solvent; and the solvent just touches the tip of the paper

Start line drawn with pencil

Slide 9

Chromatography - uses

  • To separate

    (a) pigments from plants; (b) dyes from ink;

    (c) amino acids from proteins for analysis.

  • To identify poisons and drugs, or to detect traces of unlawful dyes or other additives in foodstuffs.

  • To determine the purity of a given substance.

Slide 10

Criteria of Purity

  • Pure substance

    - substance with no other substances mixed with them

    • has fixed (sharp) melting point and boiling point

  • Mixture

    • A mixture does not have definite properties.

    • It melts or boils over a range of temperatures

Slide 11

Checking the Purity

  • Checking its melting point

  • Checking its boiling point

    No two substances have the same pair of melting and boiling pts. Hence melting and boiling pts. can be used to identify a substance.

    Using chromatography

Slide 12

Determination of boiling point

Slide 13

Checking purity - with mpt. & bpt

  • Impurites will lower the melting point and raise the boiling point

  • For an impure substance, the temperature does not stay constant during boiling/melting.

Slide 14

Checking purity - using chromatography

  • A pure substance will give only one spot in the chromatogram.

Mixture

Pure substance

Slide 15

Produces only one spot

Produces more than one spot

Chromatography

Can be differentiated by

Mixtures

Pure substances

Has sharp melting/boiling point

Melts/boils over a range of temperatures

Melting/Boiling pt.


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