RP6: Tests for alcohol , aldehyde , alkene and carboxylic acid

Question 1

how do you get for alkenes and what’s the observation

Answer 1

• To 0.5cm3 of bromine water in a test tube add a few drops of the unknown and shake
  Observation : Alkenes should decolourise bromine water

Question 2

what are the tests for an aldehyde ( Tollens reagent )

Answer 2

Tollens reagent - former by mixing ammonia and silver nitrate . [Ag(NH3)2]+
Conditions : heat gently
Reaction : Aldehydes only are oxidised by Tollens reagent into a carboxylic acid and the silver ions are reduced to silver atoms
Observation : With aldehydes , a silver mirror forms coating the inside of the test tube . Ketones = no change
CH3CHO + 2Ag+ + H2O => CH3COOH + 2Ag + 2H+

Question 3

what’s the tollens reagent method

Answer 3

• Place 1cm3 of silver nitrate solution in each of two clean boiling tubes .
• add one drop of sodium hydroxide solution to form a ppt of silver oxide
• add ammonia solution dropwise until a clear , colourless solution is formed .
• add a few drops of the unknown and leave it in the water bath for a few minutes

Question 4

What’s the test for aldehydes ( Fehlings solution )

Answer 4

Reagent : Fehlings solution containing blue Cu2+ ions
Conditions : heat gently
Reaction : Aldehudes only are oxidised by Fehlings solution into a carboxylic acid and the copper (II) ions are reduced to copper (I) oxide .
Observation : Aldehydes : Blue Cu2+ ions in solution change to a red ppt of Cu2O . Ketones do not react .
CH3CHO + 2Cu2+ + 2H2O => CH3COOH + Cu2O + 4H+

Question 5

what’s the method for fehlings solition

Answer 5

• place 1cm3 Fehlings A into each of two boiling tubes , and then add Fehlings B until the blue ppt redissolves .
• Add a few drops of the unknown and leave in the water bath for a few mins

Question 6

what’s the method for testing for a carboxylic acid

Answer 6

• to 0.5cm3 of ur unknown solution in a test tube add a small amount of sodium carbonate solid and observe

Question 7

what’s the observation for testing for a carboxylic acid

Answer 7

It will fizz and produce carbon dioxide
or effervescence
2CH3CO2H + Na2CO3 => 2CH3CO2-Na+ + H2O + CO2

Question 8

what’s the method for halogenoalkane

Answer 8

• arrange three test tubes in a row and add three drops of halogenoalkane
• add 4cm3 of 0.02moldm-3 silver nitrate to each halogenoalkane
• without delay , put all three test tubes simultaneously on a hot water bath
• not the order in which precipitate appear

Question 9

what is the reagent and result for acyl chloride

Answer 9

reagent : silver nitrate
result : vigorous reaction - steamy fumes of HCl - rapid white ppt of AgCl