Qualitative Analysis of Organic Compounds Vocabulary

Vocabulary-style flashcards covering the qualitative analysis techniques for identifying elements in organic compounds as per the lecture notes.

Carbon Detection Result

Carbon present in the compound is oxidised to carbon dioxide, which is tested with lime-water to develop turbidity ($CaCO_3$).

Hydrogen Detection Result

Hydrogen is oxidised to water, which is tested with anhydrous copper sulphate, turning it from white to blue ($CuSO_4 \times 5H_2O$).

Lassaigne's Test

A test used to detect nitrogen, sulphur, halogens, and phosphorus where elements are converted from covalent to ionic form by fusing the organic compound with sodium metal.

Sodium Fusion Extract

The liquid extract produced by boiling the fused mass of sodium metal and the organic compound with distilled water.

Prussian Blue Colour

The color confirming the presence of nitrogen in the sodium fusion extract test, caused by the formation of iron(III) hexacyanoferrate (II) ($Fe_4[Fe(CN)_6]_3 \times xH_2O$).

Sulphur Test (Lead Acetate)

A test where the sodium fusion extract is acidified with acetic acid and treated with lead acetate to form a black precipitate of lead sulphide ($PbS$).

Sulphur Test (Sodium Nitroprusside)

A test where treating the sodium fusion extract with sodium nitroprusside results in a violet colour ($[Fe(CN)_5NOS]^{4-}$).

Sodium Thiocyanate ($NaSCN$)

A compound formed during sodium fusion when both nitrogen and sulphur are present; it produces a blood red colour ($[Fe(SCN)]^{2+}$) with $Fe^{3+}$.

Chlorine Test (Silver Nitrate)

Presence indicated by a white precipitate ($AgCl$) that is soluble in ammonium hydroxide ($NH_4OH$).

Bromine Test (Silver Nitrate)

Presence indicated by a yellowish precipitate ($AgBr$) that is sparingly soluble in ammonium hydroxide ($NH_4OH$).

Iodine Test (Silver Nitrate)

Presence indicated by a yellow precipitate ($AgI$) that is insoluble in ammonium hydroxide ($NH_4OH$).

Removing Cyanide/Sulphide interference

The process of boiling the sodium fusion extract with concentrated nitric acid ($HNO_3$) to decompose these ions before testing for halogens.

Phosphorus Detection Result

The formation of a yellow colouration or precipitate of ammonium phosphomolybdate ($(NH_4)_3PO_4 \times 12MoO_3$) after heating the compound with sodium peroxide and treating it with ammonium molybdate and nitric acid.

Carbon Detection

The process of heating an organic compound with copper (II) oxide ($CuO$) to produce carbon dioxide, which is tested with lime-water ($Ca(OH)_2$) to develop turbidity representing the formation of $CaCO_3$.

Hydrogen Detection

The process of heating an organic compound with copper (II) oxide ($CuO$) to produce water ($H_2O$), which turns white anhydrous copper sulphate ($CuSO_4$) blue by forming $CuSO_4 \times 5H_2O$.

Lassaigne's test

A qualitative analysis method where nitrogen, sulphur, halogens, and phosphorus in an organic compound are converted from covalent to ionic form by fusion with sodium metal ($Na$).

Sodium Fusion Extract

The liquid obtained by boiling the fused mass produced during Lassaigne's test with distilled water to extract sodium cyanide, sodium sulphide, and sodium halides.

Nitrogen Test (Prussian Blue)

A test for nitrogen where the sodium fusion extract is boiled with iron(II) sulphate ($FeSO_4$) and acidified with concentrated sulphuric acid ($H_2SO_4$) to form iron(III) hexacyanoferrate (II) ($Fe_4[Fe(CN)_6]_3 \times xH_2O$).

Lead Acetate Test

A test for sulphur where sodium fusion extract is acidified with acetic acid and treated with lead acetate to produce a black precipitate of lead sulphide ($PbS$).

Sodium Nitroprusside Test

A test for sulphur identification where treating the sodium fusion extract with sodium nitroprusside ($Na_2[Fe(CN)_5NO]$) results in a violet colour from the complex $[Fe(CN)_5NOS]^{4-}$.

Sodium Thiocyanate ($NaSCN$)

A compound formed during sodium fusion when both nitrogen and sulphur are present in the organic compound, which produces a blood red colour with $Fe^{3+}$ ions.

Chlorine Test

Detected when sodium fusion extract is acidified with nitric acid ($HNO_3$) and treated with silver nitrate ($AgNO_3$), producing a white precipitate ($AgCl$) soluble in ammonium hydroxide ($NH_4OH$).

Bromine Test

Detected when sodium fusion extract is treated with nitric acid ($HNO_3$) and silver nitrate ($AgNO_3$), producing a yellowish precipitate ($AgBr$) sparingly soluble in ammonium hydroxide ($NH_4OH$).

Iodine Test

Detected when sodium fusion extract is treated with nitric acid ($HNO_3$) and silver nitrate ($AgNO_3$), producing a yellow precipitate ($AgI$) insoluble in ammonium hydroxide ($NH_4OH$).

Nitric Acid Boil (Pre-Halogen Test)

A step required if nitrogen or sulphur are present to decompose cyanide ($NaCN$) or sulphide ($Na_2S$) ions that would otherwise interfere with the silver nitrate test for halogens.

Phosphorus Test (Ammonium Molybdate)

A test where a compound is oxidised with sodium peroxide to phosphate, then treated with nitric acid ($HNO_3$) and ammonium molybdate ($(NH_4)_2MoO_4$) to form a yellow precipitate of ammonium phosphomolybdate ($(NH_4)_3PO_4 \times 12MoO_3$).