Photo AI
An ester and an acid are both listed as additives on a food label - HSC - SSCE Chemistry - Question 21 - 2013 - Paper 1
Question 21
An ester and an acid are both listed as additives on a food label. (a) Why is acid used as a food preservative? Many microorganisms that cause spoilage of food ca... show full transcript
Worked Solution & Example Answer:An ester and an acid are both listed as additives on a food label - HSC - SSCE Chemistry - Question 21 - 2013 - Paper 1
Step 1
Why is acid used as a food preservative?
Answer
A food preservative prevents spoilage by creating an acidic environment. Many microorganisms which lead to food spoilage thrive in neutral or alkaline pH levels. By adding an acid, the pH is lowered, making it difficult for these microorganisms to survive. For example, organic acids like citric acid or acetic acid are commonly used for this purpose.
Step 2
Explain, on a labelled diagram, why reflux is used to produce an ester.
Answer
Reflux is used in esterification reactions to ensure that the reaction mixture is heated for an extended period while preventing the loss of volatile components, such as reactants or products.
A labeled diagram should include:
- A round-bottom flask containing the reactants (an alcohol and a carboxylic acid) mixed with a small amount of acid catalyst.
- A condenser connected to the top of the flask, which allows vapors to cool and return to the flask, maintaining the reaction at a constant temperature without losing any material.
- Heat source shown below the flask.
This setup ensures that the reaction can achieve a higher yield and complete conversion of reactants into the ester.