fucntional group tests

Question 1

how to test for alkenes, whats the positive result?

Answer 1

-add bromine water and shake
- if alkene water will go from orange to colourless
-if not alkene, water will remain colourless

Question 2

what is the test for acohol, whats the observation for a postive result?

Answer 2

• add ACIDIFED potassium dichromate
  -if alchol is present the solution will turn from orange to green

Question 3

can acidified potassium dichromate identify all alcohols?

Answer 3

• no just ditinguish between primary or secondary
• however the observations are the same for both primary and secondary

Question 4

test for aldehyde, observation for it

Answer 4

-add tollens reagent and warm
- postive result would be a silver mirror

Question 5

how to make up the tollens reagent?

Answer 5

-add 2cm silver nitrate
-add sodium hydroxide (light brown precipitate should form)
- add dilute ammonia until brown dissapears
- place in water bath with the aldehyde/ketone

Question 6

another test for aldhydes?

Answer 6

-add fehlings solution
-solution turns from blue to brick red, when aldehyde present

Question 7

test for carboxylic acids, observation

Answer 7

-add hydrogen carbonate/carbonate e.g hydrogen carbonate
- positive result would be effervesence and gas produced

Question 8

test for halogenoalkanes, observation?

Answer 8

-warm with sodium hydroxide
-add nitric acid
- add silver nitrate
-a PRECIPITATE should form

Question 9

how to further test for primary and secondary alchols after using acidified potassium dichromate?

Answer 9

-oxidise and then distill the produvcts from the previous test
- then use fehlings or benedcits test

Question 10

what is the role of acidifed potassium dichromate in the test for alcohols?

Answer 10

-is a oxidising agent, so reduces itself from Cr2O7- to Cr3+