6 (3.6) Test for alcohol, aldehyde, alkene, carboxylic acid

Question 1

Test for alcohol: metal

Answer 1

1. Add a small piece of metallic sodium​ ​to alcohol.
2. Produces hydrogen gas which is shown by ‘squeaky pop’ test.

Question 2

Safety precautions for test for alcohol: metal

Answer 2

3. Dispose any excess sodium safely using the beaker of ethanol provided. (Sodium will completely react with the excess ethanol in order to be safely washed away because if any water comes into contact with the sodium there is a serious fire risk)

Question 3

Test for alcohol: potassium dichromate

Answer 3

1. add acidified potassium dichromate to the solution, heat in hot water bath
2. Primary and secondary alcohols will reduced from orange dichromate(VI) ions to green chromium(III) ions.
3. It will remain orange if a tertiary alcohol is present.

Question 4

Test for alkene?

Answer 4

-add bromine water, shake tube
-bromine water decolourises from orange if alkene present

Question 5

Test for carboxylic acid?

Answer 5

-add solid sodium carbonate
-effervescence/ fizzing of CO2 gas
-bubble through limewater- turns cloudy if CO2 produced

Question 6

Formula for limewater turning cloudy?

Answer 6

Ca(OH)2 + CO2 —> CaCO3 + H2O

Question 7

Equation for testing for alcohol test? (Ethanol)

Answer 7

3CH3CH2OH + Cr2O7^2- + 8H+ —> 3CH3CHO + 2Cr^3+ + 7H2O

Question 8

Test for halogenoalkand?

Answer 8

-add NaOH solution + warm
-add dilute nitric acid + silver nitrate solution
-if haloalkane present- precipitate form

Question 9

Results for tests for halogenoalkanes?

Answer 9

Chloride ions (Cl-) = white ppt
Bromide ions (Br-) = cream ppt
Iodide ions (I-) = Yellow ppt

Question 10

Test for aldehyde?

Answer 10

-add Fehlings solution to sample
-if aldehyde present- red ppt forms