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.

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

3. Chromatography

4. Chromatography

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

6. Chromatography simulation
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

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

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.

10. Criteria of Purity Pure substance Mixture
- 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

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

12. Determination of boiling point

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.

14. Checking purity - using chromatography
A pure substance will give only one spot in the chromatogram.
Mixture
Pure substance

15. Can be differentiated by
Produces more than one spot
Produces only 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.