JEE Chemistry Principles Related to Practical Chemistry

Principles Related to Practical Chemistry PDF Notes, Important Questions and Synopsis

SYNOPSIS

Qualitative analysis of organic compounds: Analysis involving detection of all elements present in an organic compound.

Detection of carbon and hydrogen: Carbon and hydrogen are detected by heating the compound with copper (II) oxide. Carbon present in the compound is oxidised to carbon dioxide and hydrogen to water. Carbon dioxide is tested with lime water. Carbon dioxide makes lime water milky and develops turbidity. Water is tested with anhydrous copper sulphate, which becomes blue on absorbing moisture.

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Detection of nitrogen: The sodium fusion extract (prepared by boiling fused mass of the compound and sodium metal in distilled water) is boiled with FeSO₄(iron (II) sulphate) and then acidified with concentrated sulphuric acid. The formation of a Prussian blue colour confirms the presence of nitrogen.

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a. On adding lead acetate to acidified sodium fusion extract, the formation of a black precipitate confirms the presence of sulphur.
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2. b. On adding sodium nitroprusside to acidified sodium fusion extract, the appearance of violet colour indicates the presence of sulphur.
  
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Detection of halogens: On adding a silver nitrate solution to sodium fusion extract acidified with nitric acid, a white precipitate (soluble in ammonium hydroxide) shows the presence of chlorine, a yellowish precipitate (sparingly soluble in ammonium hydroxide) shows the presence of bromine and a yellow precipitate (insoluble in ammonium hydroxide) shows the presence of iodine.

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Detection of phosphorus: The compound containing phosphorus is heated with an oxidising agent (sodium peroxide) which oxidises phosphorus to phosphate. The solution is boiled with nitric acid and then treated with ammonium molybdate. A yellow colouration or precipitate indicates the presence of phosphorus.

$begin mathsize 12px style table attributes columnalign left end attributes row cell text end text Na subscript 3 PO subscript 4 text end text plus text end text 3 HNO subscript 3 text end text rightwards arrow with blank on top text end text straight H subscript 3 PO subscript 4 text end text plus text end text 3 NaNO subscript 3 end cell row cell straight H subscript 3 PO subscript 4 text end text plus stack text end text 12 text end text open parentheses NH subscript 4 close parentheses subscript 2 MoO subscript 4 with table attributes columnalign left end attributes row Ammonium row molybdate end table below text end text plus text end text 21 HNO subscript 3 text end text rightwards arrow with blank on top text end text stack open parentheses NH subscript 4 close parentheses subscript 3 PO subscript 4.12 MoO subscript 3 with table attributes columnalign left end attributes row cell text end text Ammonium end cell row phosphomolybdate end table below text end text plus text end text 21 text end text NH subscript 4 NO subscript 3 text end text plus text end text 12 straight H subscript 2 straight O end cell end table end style$