3.6 Organic Analysis

Question 1

How do you test for alkenes?

Answer 1

Shake with bromine water, result is bromine water going from orange to colourless

Question 2

How do you test for halogenoalkanes?

Answer 2

Add NaOH (aq) and warm acidify with HNO3 then add AgNO3 (aq)
Result: precipitate of AgX (for Cl - white, for Br - cream, for I - yellow)

Question 3

How do you test for alcohols?

Answer 3

Add acidified K2Cr2O7 and heat
Result: colour change from orange to green for primary and secondary alcohols (no change for tertiary alcohols)

Question 4

How do you test for aldehydes (2)

Answer 4

1. Warm with Fehlings solution, result: brick red precipitates
2. Warm with Tollen’s, result: “silver mirror”

Question 5

How do you test for carboxylic acids?

Answer 5

Add Na2CO3 (aq), result: CO2 (g) given off - effervescence

Question 6

What is mass spectrometry? How does it work?

Answer 6

Used to find the relative molecular masses of organic compounds
Compound is dissolved in solution, ionised by a high voltage supply (to mostly 1+) accelerated by a negatively charged plate, becomes a beam of ionised molecules, reach detector and cause a current to flow. Time of flight used to work out m/z value and plot graph