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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
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.
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
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
- substance with no other substances mixed with them
has fixed (sharp) melting point and boiling point
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.
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.