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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? (b) Explain, on a labelled diagram, why reflux is u... 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
Acids are used as food preservatives primarily because they create an environment that is unfavorable for many microorganisms. Most bacteria and mold cannot thrive in low pH conditions, which are typically produced by adding an acid to food. This helps to slow down spoilage and extend the shelf life of the food.
Step 2
Explain, on a labelled diagram, why reflux is used to produce an ester.
Answer
Reflux is used in the production of esters to allow the reaction between an alcohol and an acid (usually a carboxylic acid) to take place efficiently without losing any of the volatile components. The apparatus typically includes a round-bottom flask, a heat source, a condenser, and a means to stir the mixture.
- Heat Application: The mixture is heated to encourage the reaction, which produces vapor.
- Condensation: The vapor rises and enters the condenser, where it cools and condenses back into liquid form.
- Prevention of Loss: This liquid returns to the flask, ensuring that reactants and products remain in the reaction mixture, allowing for an equilibrium to establish, and ultimately leading to a higher yield of the ester.
A well-labelled diagram should illustrate a round-bottom flask connected to a condenser, with indications for the heat source and the flow of materials.