Oxidation of food SQA edition

In carbon compounds, what does oxidation mean?

Oxidation is an increase in the oxygen to hydrogen ratio.

In carbon compounds, what does reduction mean?

Reduction is a decrease in the oxygen to hydrogen ratio.

What oxidising agents can be used for alcohols?

Hot copper(II) oxide

Acidified dichromate(VI) solution

What happens when primary alcohols are oxidised?

They are oxidised to aldehydes, and then further to carboxylic acids.

What happens when secondary alcohols are oxidised?

They are oxidised to ketones.

Can tertiary alcohols be oxidised by copper(II) oxide or acidified dichromate?

No, tertiary alcohols cannot be oxidised using these oxidising agents.

What are the visible changes when alcohols are oxidised with these agents? (copper (II) oxide turns from what to what)(acidified dichromate turns from what to what)

• Copper(II) oxide turns from black to brown

• Acidified dichromate(VI) turns from orange to green

What functional group is present in aldehydes and ketones?

The carbonyl group: C=O

Can aldehydes be oxidised?

Can be oxidised to carboxylic acids

Can ketones be oxidised?

Cannot be further oxidised under normal conditions

How can you test for an aldehyde?

• Fehling’s solution: Blue → Brick red precipitate

• Tollens’ reagent: Colourless → Silver mirror

• Acidified dichromate: Orange → Green

Colour change for Fehlings solution

Blue → Brick red precipitate

Colour change for Tollen’s reagent

Colourless → silver mirror

What is the colour change for acidified dichromate?

Orange → green (The colour change for acidified dichromate indicates the reduction of chromium ions during oxidation reactions)

What is a common use of aldehydes?

Many flavour and aroma molecules are aldehydes.

What causes the rancid flavour in oxidised food?

Oxidation of edible oils due to oxygen in the air.

What are antioxidants?

Molecules that prevent unwanted oxidation reactions.

How do antioxidants work?

They are easily oxidised and oxidise in place of the compounds they protect.

How can antioxidants be identified in a redox equation?

The antioxidant is the substance being oxidised in the redox reaction.