3.6 Organic analysis

Question 1

Test for alkenes and observations:

Answer 1

Test - add bromine water

Observation - orange to colourless if alkene is present (decolourises)

Question 2

Test for types of alcohols and observations:

Answer 2

Test - add acidified potassium dichromate and warm

Observations:
1* and 2* - orange to green
3* - remains orange (resists oxidation)

Question 3

Test for aldehydes and observations:

Answer 3

Test 1 - tollen’s reagent (warm)
Observations - silver mirror

Test 2 - Fehling’s solution
Observations - blue to brick-red precipitate

Question 4

Test for carboxylic acids and observations:

Answer 4

Test - add sodium carbonate/hydrogencarbonate

Observation - effervescence (CO2)

Question 5

Test for halogenoalkanes:

Answer 5

Test - add aqueous silver nitrate and warm

Observations -
Cl: white precipitate
Br: cream precipitate
I: yellow precipitate

Question 6

What is infrared spectroscopy?

Answer 6

Detects specific covalent bonds present within a compound

Question 7

Why do greenhouse gases absorb infrared radiation?

Answer 7

Their respective (polar) bonds absorb the radiation, causing the bonds to vibrate/rotate

Question 8

Why is water vapour a more effective greenhouse gas than CO2?

Answer 8

It absorbs the infrared radiation over a larger range

Question 9

KEY DEFINITION: molecular ion peak

Answer 9

The line with the largest m/z ratio - gives the Mr of the compound