Oxidation and Chemistry of Cooking Flashcards
How are alcohols classified into types and describe the classifying feature of each?
Classified by the position of the hydroxyl group
Primary - -OH group bonded to carbon with only one other carbon attached, ie at end of chain
Secondary - OH group to carbon with two carbons attached, i.e an intermediate carbon.
Tertiary - OH group bonded to carbon with three carbons attached, i.e an intermediate carbon with a branch.
Describe the oxidation of a primary alcohol.
Primary alcohol - aldehyde - carboxylic acid
Describe the oxidation of a secondary alcohol.
Secondary alcohol - ketone
Describe the oxidation of a tertiary alcohol.
Not readily oxidised
What are the suitable oxidising agents for the oxidation of an alcohol?
Acidified potassium dichromate and Copper (II) Oxide
What is the colour change observed when acidified potassium dichromate is used as oxidising agent?
orange - blue/green
Describe the experimental procedure for oxidation of an alcohol with a mild oxidising agent e.g acidified dichromate
alcohol placed in test tube with oxidising agent and test tube placed in hot water bath
How can aldehydes and ketones be identified?
The presence of the carbonyl group, C to O double bond
Where is the carbonyl group in a aldehyde?
The end of the carbon chain.
Where is the carbonyl group in a ketone?
An intermediate carbon.
What is the ending given to a ketone?
-one
What is the ending given to a aldehyde?
-al
What kind of chemical used to distinguish between aldehydes and ketones?
An oxidising agent, since aldehydes oxidise to carboxylic acids and ketones do not readily oxidise.
What are suitable oxidising agents for distinguishing between aldehydes and ketones? And what colour change is observed?
Fehling’s solution - blue -> orange/red
Tollen’s reagent - colourless -> silver mirror
Acidified potassium dichromate - orange ->green/blue
What is oxidation (carbon compounds)
A increase in the oxygen - Hydrogen ratio
What is reduction (carbon compounds)
A decrease in the O:H ratio
What is produced when carboxylic acids are reduced?
Carboxylic acid - aldehyde - primary alcohol.
Why are carboxylic acids known as weak acids?
They produce H+ ions when added to water, but not to the same extent as strong acids
What is produced when a carboxylic acid is reacted with a base?
Salts which contain the carboxylate ion (COO-) and water
What are salts of carboxylic acids used for?
Preservatives in the food industry
What kind of molecules are many aroma and flavour molecules?
Aldehydes and Ketones
What reaction causes food to spoil?
Oxidation
What is added to foods to prevent it spoiling?
Antioxidants.
What happens when edible oils are oxidised?
They develop a rancid flavour
