Organic analysis

Question 1

What are some simple tests?

Answer 1

• acidic
• bonding present
  
  • solid, liquid or gas
• soluble
  
  • polar groups or not
• burn with a smoky flame
  
  • suggests high C:H, possiubly aromatic

Question 2

What is the test for an alkene, what is the result?

Answer 2

• shake with bromine water
• red-brown colour disappears

Question 3

What is the test for a halogenoalkane and what is the indication of a +ve result

Answer 3

• add aqueous NaOH and warm
• acidify with HNO3
• add aqueous AgNO3
• ppt of AgX forms

Question 4

What is the test for a alcohol and what is the indication of a +ve result

Answer 4

• add acidified potassium dichromate
• orange colour turns green with primary or secondary alcohols
  
  • also with aldehydes

Question 5

What are the tests for an aldehyde?

Answer 5

• warm with Fehling’s soln
  
  • blue to red ppt
• warm with Tollens soln
  
  • silver mirror forms
• add acidified potassium dichromate
  
  • orange to green

Question 6

What is the test for a carboxylic acid>?

Answer 6

• add aqueous sodium hydrogencarbonate
  
  • bubbles observed
  • CO2 given off

Question 7

Suggest one reason why Tollens’ reagent is used as the oxidising agent in the specific test for aldehydes rather than the less expensive acidified potassium dichromate(VI).

Answer 7

Dichromate(VI) will also oxidise / give a positive test with alcohols