| Aim | To identify the functional groups present in organic compounds – Unsaturation, alcoholic, phenolic, aldehydic, ketonic, carboxylic, and amino (Primary) groups. |
| Apparatus Required | Test tubes Dropper Test tube holder Test tube rack Water bath Bunsen burner Glass rod Conc. H2SO4 FeCl3 solution Fehling’s solution A and B Sodium bicarbonate solution 2,4-DNPH solution Ninhydrin solution |
| Theory | Functional groups are groups of atoms in a molecule that determine its chemical and physical properties. Some common functional groups in organic compounds include unsaturation, alcoholic, phenolic, aldehydic, ketonic, carboxylic, and amino (Primary) groups. |
| Procedure | Test for unsaturation: Take a small amount of the organic compound and add a few drops of bromine water to it. Observe the colour change. If the compound contains unsaturation, the orange-brown colour of bromine water will disappear. Test for alcoholic group: Take a small amount of the organic compound and add a few drops of conc. H2SO4 to it. Heat the mixture gently in a water bath. Observe any effervescence or formation of a sweet-smelling gas (ether). To confirm the presence of an alcoholic group, add a few drops of sodium bicarbonate solution to the mixture. The formation of a brisk effervescence confirms the presence of an alcoholic group. Test for phenolic group: Take a small amount of the organic compound and add a few drops of FeCl3 solution to it. Observe any colour change. If the compound contains a phenolic group, the colour will change to violet or blue-black. Test for aldehydic group: Take a small amount of the organic compound and add a few drops of Fehling’s solution A and B to it. Heat the mixture gently in a water bath. Observe any formation of a red precipitate. The formation of a red precipitate confirms the presence of an aldehydic group. Test for ketonic group: Take a small amount of the organic compound and add a few drops of 2,4-DNPH solution to it. Observe any formation of a yellow or orange precipitate. The formation of a yellow or orange precipitate confirms the presence of a ketonic group. Test for carboxylic group: Take a small amount of the organic compound and add a few drops of NaHCO3 solution to it. Observe any brisk effervescence, which confirms the presence of a carboxylic group. Test for primary amino group: Take a small amount of the organic compound and add a few drops of ninhydrin solution to it. Heat the mixture gently in a water bath. Observe any formation of a blue or purple colour. The formation of a blue or purple colour confirms the presence of a primary amino group. |
| Observation and Result | Unsaturation: Observation: The presence of unsaturation can be confirmed by the addition of bromine water or potassium permanganate to the compound. If the compound is unsaturated, the bromine water or potassium permanganate will be decolorized. Result Test: The bromine water or potassium permanganate test can be used to differentiate between alkenes and alkynes. Alkenes will decolorize bromine water and turn it from orange to colorless, while alkynes will decolorize bromine water more rapidly and turn it from orange to colorless. For potassium permanganate, alkenes and alkynes will both decolorize it and turn it from purple to colorless. Alcoholic: Observation: The presence of an alcoholic group can be confirmed by the addition of a few drops of sodium or potassium hydroxide to the compound, followed by the addition of a few drops of iodine solution. If an alcoholic group is present, a yellow precipitate of iodoform will be formed. Result Test: The iodoform test can be used to differentiate between primary, secondary, and tertiary alcohols. Primary alcohols will give a positive iodoform test, secondary alcohols may give a positive test but require heating, while tertiary alcohols will not give a positive test. Phenolic: Observation: The presence of a phenolic group can be confirmed by the addition of ferric chloride to the compound. If a phenolic group is present, a violet or blue-black color will be observed. Result Test: The ferric chloride test is a confirmatory test for the presence of a phenolic group. Aldehydic: Observation: The presence of an aldehydic group can be confirmed by the addition of a few drops of Tollens’ reagent (ammoniacal silver nitrate) to the compound. If an aldehydic group is present, a silver mirror will be formed. Result Test: The Tollens’ test is a confirmatory test for the presence of an aldehydic group. Ketonic: Observation: The presence of a ketonic group can be confirmed by the addition of a few drops of 2,4-dinitrophenylhydrazine reagent to the compound. If a ketonic group is present, a yellow or orange precipitate will be formed. Result Test: The 2,4-dinitrophenylhydrazine test is a confirmatory test for the presence of a ketonic group. Carboxylic: Observation: The presence of a carboxylic group can be confirmed by the addition of a few drops of sodium bicarbonate to the compound. If a carboxylic group is present, effervescence (bubbling) will occur due to the release of carbon dioxide gas. Result Test: The sodium bicarbonate test is a confirmatory test for the presence of a carboxylic group. Amino (Primary): Observation: The presence of a primary amino group can be confirmed by the addition of a few drops of ninhydrin reagent to the compound. If a primary amino group is present, a blue or purple color will be formed. Result Test: The ninhydrin test is a confirmatory test for the presence of a primary amino group. |