Required practical 6

Question 1

How to test for the presence of an alcohol

Answer 1

Use metallic sodium

Question 2

Test for alcohol - step 1

Answer 2

Add a small piece of metallic sodium to the solution

Question 3

Test for alcohol - step 2

Answer 3

This produces hydrogen which can be tested for using squeaky pop test

Question 4

Test for alcohol - step 3

Answer 4

Dispose of sodium safely into provided beaker of ethanol

Question 5

Why must sodium be disposed off into ethanol

Answer 5

The sodium will completely react with the excess ethanol to be safely washed away as if any water comes into contact with the sodium, there is serious fire risk

Question 6

Test to distinguish alcohols

Answer 6

Acidified potassium dichromate

Question 7

Distinguish alcohol - step 1

Answer 7

Add acidified potassium dichromate to the solution

Question 8

Distinguish alcohol - result

Answer 8

Primary and secondary - orange solution to green solution
Tertiary - solution remains orange

Question 9

Why does solution turn from orange to green

Answer 9

Primary and secondary alcohols become oxidised, which reduces the orange dichromate (IV) ions to green chromium (III) ions

Question 10

How to test for aldehyde

Answer 10

Fehlings

Question 11

Fehlings - step 1

Answer 11

In a clean test tube, mix equal volumes of fehlings A and fehlings B solutions

Question 12

What is the resutling colour of fehlings solution

Answer 12

Clear dark blue

Question 13

Fehlings - step 2

Answer 13

Add 5 drops of this reagent to test tube, along with a few anti bumping granules, and then add the aldehyde

Question 14

Fehlings - step 3

Answer 14

Gently warm the test tube in a beaker of hot water, slowly bringing to boil - leave at that temperature for a few minutes

Question 15

Fehlings - step 4

Answer 15

Carefully remove the test tube from the water and leave the contents to stand for a while

Question 16

Fehlings - result

Answer 16

Presence of an aldehyde will cause brick red precipitate to form

Question 17

Why does brick red precipitate form

Answer 17

The Cu2+ ions are reduced to Cu+ which then form Copper(I)Oxide

Question 18

How to test for alkene

Answer 18

Bromine water

Question 19

Test for alkene - step 1

Answer 19

Add 1cm3 bromine water to 2 drops of solution

Question 20

Test for alkene - step 2

Answer 20

Shake the test tube vigorously from side to side

Question 21

Test for alkene - result

Answer 21

Bromine water decolourises from orange in the presence of an alkene

Question 22

How to test for carboxylic acid

Answer 22

Sodium carbonate

Question 23

Test for carboxylic acid - step 1

Answer 23

Add a spatula of sodium carbonate into test tube and add 2cm3 solution with pipette

Question 24

Test for carboxylic acid - step 2

Answer 24

Collect the gas produced and bubble through lime water

Question 25

Test for carboxylic acid - result

Answer 25

Lime water turns cloudy in the presence of carboxylic acid as carbon dioxide is produced

Question 26

How to test for halogenoalkane

Answer 26

Sodium hydroxide and silver nitrate

Question 27

Test for halogenoalkane - step 1

Answer 27

Using teat pipette, add 5 drops of halogenoalkane to 1cm3 NaOH solution

Question 28

What is the purpose of the NaOH solution

Answer 28

OH- ions displace the halide ions through nucleophilic substitution

Question 29

Test for halogenoalkane - step 2

Answer 29

Warm the test tube gently using beaker of hot water

Question 30

Test for halogenoalkane - step 3

Answer 30

Acidify the contents of the test tube by adding 2cm3 nitric acid

Question 31

What is the purpose of the nitric acid

Answer 31

Removes carbonate and hydroxide impurities which may also form a precipitate

Question 32

Test for halogenoalkane - step 4

Answer 32

Add 1cm3 silver nitrate

Question 33

Test for halogenoalkane - result

Answer 33

Precipitate will form
AgCl - white
AgBr - cream
AgI - yellow