/ 15 []

Criteria of Purity - PowerPoint Slides

Download Presentation

Criteria of Purity

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use only and may not be sold or licensed nor shared on other sites. SlideServe reserves the right to change this policy at anytime.While downloading, If for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript

Criteria of purity

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.



  • 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







  • 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



  • 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



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

Chromatography uses

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.

Criteria of purity1

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

Checking the purity

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

Determination of boiling point

Determination of boiling point

Checking purity with mpt bpt

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.

Checking purity using chromatography

Checking purity - using chromatography

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


Pure substance

Produces only one spot

Produces more than one spot


Can be differentiated by


Pure substances

Has sharp melting/boiling point

Melts/boils over a range of temperatures

Melting/Boiling pt.