Unit 2(a) - Oxidation of Food and the Chemistry of Cooking - Alcohols, Carboxylic Acids, Aldehydes and Ketones Flashcards
What is the general formula for an alcohol?
CnH2n+1OH
How do alcohol isomers differ?
Position of hydroxyl group
What functional group is present in alcohols?
OH (hydroxyl group)
What is a diol/triol?
Diol - two hydroxyl groups
Triol - three hydroxyl groups
What are some properties of alcohols?
- Polar liquids
- Overall polar molecule
- More viscous than similar sized liquid alkane
- Evaporate more slowly than similar sized liquid alkane
- Significantly higher melting and boiling points than similar sized alkanes
What are the three types of alcohols?
- Primary
- Secondary
- Tertiary
What is a primary alcohol?
An alcohol with only one carbon atom joined to the carbon bonded to the hydroxyl group
What is a secondary alcohol?
An alcohol with two carbon atoms joined to the carbon bonded to the hydroxyl group
What is a tertiary alcohol?
An alcohol with three carbon atoms joined to the carbon bonded to the hydroxyl group
What is mild/severe oxidation?
Mild: affects just functional group
Severe: affects whole molecule
What do primary alcohols oxidise to?
Aldehyde, then Carboxylic acid
What does a secondary alcohol oxidise to?
Ketone
Why do tertiary alcohols not oxidise?
No hydrogens to lose
What is the general formula for an aldehyde?
RCHO, where R is an alkyl group
How are aldehydes named?
Corresponding alkyl name with ending replaced with -AL
What is the general formula for a ketone?
RCOR’, where R and R’ are alkyl groups
How are ketones named?
Corresponding alkane name with the ending changed to -ONE
What are some properties of aldehydes and ketones?
- Very polar
- Higher mps and bps than alkanes of a similar size
- Smaller aldehydes/ketones are water soluble
Give 3 oxidising agents for primary and secondary alcohols
- Acidified potassium dichromate solution (orange to green)
- Benedict’s/Fehling’s solution (blue to brick red
- Tollen’s reagent (silver aqueous to silver solid)
What is the general formula for a carboxylic acid?
CnH2n+1COOH
What are some properties of carboxylic acids?
- Colourless liquid
- pH 2-3
- Sharp smell
When do foods oxidise?
When exposed to oxygen in the air
What happens to fats and oils when oxidised?
Degradation of long fatty acid chains and formation of short chain products
Which molecule mediates the oxidation of fats and oils?
Free radicals
How can oxidation of foods be slowed down?
- Reducing the temperature
- Packaging under and vacuum or under an inert gas
- Addition of antioxidants
What are antioxidants?
Molecules that reduce the rate of oxidation
What is a free radical?
A highly reactive species containing an unpaired electron
How do antioxidants work?
They oxidise themselves to donate an electron to stabilise the free radical
Give an example of a natural antioxidant
Vitamin C or vitamin E
Give an example of a synthetic antioxidant
Butylated hydroxyanisole
What is accurately known in a standard solution?
Concentration
How is a standard solution prepared?
- Dissolve weighed substance in deionised water
- Pour solution through a filter funnel into a graduated flask
- Rinse out beaker with deionised water to make sure all substance is used
- Continue to add deionised water until desired volume is reached
- Stopper flask and invert to ensure proper mixing
Why is deionised water used for preparing standard solution?
Ensure that no other ions interfere with the reaction
