organic analysis

Alcohols

Alcohol Test and result

Primary (1°) and secondary (2°) Add acidified potassium dichromate and warm. Orange → green

Tertiary (3°) Not oxidised. Solution remains orange

Aldehydes Tollens’ reagent

Add Tollens’ reagent and warm gently.

Positive result: silver mirror forms.

If no aldehyde is present: solution remains colourless.

AldehydesFehling’s solution

Add Fehling’s solution and heat.

Positive result: brick-red precipitate.

If no aldehyde is present: solution remains blue.

Alkenes

Reagent: bromine water.

Positive result: orange-brown → colourless.

This shows the presence of a carbon–carbon double bond (C=C).

Carboxylic acids

Add sodium carbonate.

The acid reacts to produce carbon dioxide (CO₂).

Bubble the gas through limewater.

Positive result: limewater turns cloudy.

Mass spectrometry

Used to identify compounds and determine their molecular formula.

High-resolution mass spectrometry (HRMS):

Measures relative molecular mass () to several decimal places.

Uses precise atomic masses.

Helps determine a compound’s molecular formula.

Infrared (IR) spectroscopy

IR radiation is passed through a sample.

Different bonds absorb different amounts of IR radiation.

The absorption produces a spectrum.

Characteristic absorptions help identify bonds and functional groups.

Infrared absorption and global warming

Infrared absorption by atmospheric gases helps trap heat in the Earth’s atmosphere.

This natural effect is important for life on Earth.

Human-released chemicals, such as CFCs, enhance this heating effect.

This contributes to global warming.