Organic Analysis Flashcards
Identification of alkene by test-tube reactions
Reagent: Bromine water
Result: Orange colour decolourises
Identification of aldehyde by test-tube reactions
Reagent: Tollens’ reagent
Result: Silver mirror formed
OR
Reagent: Fehling’s solution
Result: Blue solution to red precipitate
Identification of carboxylic acid by test-tube reactions
Reagent: Sodium carbonate
Result: Effervescence of CO2 evolved
2CH3COOH + Na2CO3 → 2CH3COONa+ + H2O + CO2
What reagent can be used to identify primary/secondary alcohols and aldehyde?
Observation?
Reagent: acidified potassium dichromate (VI) and sulfuric acid
Result: Orange to green colour change
Identification of chloroalkane by test-tube reactions
Reagent: Warm with silver nitrate
Result: Slow formation of white precipitate of AgCl
Conditions, reaction and observations when using Tollens’ Reagent
Conditions: heat gently
Reaction:
-aldehydes are oxidised by Tollens’ reagent into a carboxylic acid
Ag+ ions are reduced to Ag
Observation:
Aldehydes: silver mirror coats the inside of the test tube
Ketones: no visible change
Conditions, reaction and observations when using Fehling’s solution
Conditions: heat gently
Reaction: aldehydes are oxidised by Fehling’s Solution into a carboxylic acid
-blue Cu2+ ions are reduced to CuO
Observation:
Aldehydes: Blue Cu2+ ions in solution change to a red precipitate of Cu2O
Ketones: no visible change
Conditions: heat gently
Reaction: aldehydes only are oxidised by Tollens’ reagent into a carboxylic acid. The silver(I) ions are reduced to silver atoms
Observation: with aldehydes, a silver mirror forms coating the inside of the test tube. Ketones result in no change.
How is Tollen’s reagent made
What is the active substance.
Mix aqueous ammonia and silver nitrate
Complex ion [Ag(NH3)2]+
