A group of students prepared a sample of ethanoic (acetic) acid, CH₃COOH, in the school laboratory as follows - Leaving Cert Chemistry - Question 1 - 2005
Question 1
A group of students prepared a sample of ethanoic (acetic) acid, CH₃COOH, in the school laboratory as follows.
A solution of ethanol, C₂H₅OH, in water was added in ... show full transcript
Worked Solution & Example Answer:A group of students prepared a sample of ethanoic (acetic) acid, CH₃COOH, in the school laboratory as follows - Leaving Cert Chemistry - Question 1 - 2005
Step 1
Make a rough sketch of any one of these arrangements of apparatus in your answer-book and clearly indicate the directions in which the water should flow through the condenser.
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Answer
A well-labeled diagram should include an ice bath with water inlets at the bottom and outlets at the top of the condenser. Ensure arrows indicate the direction of the water flow—entering at the bottom and exiting at the top.
Step 2
Explain why small pieces of glass or pumice stone were added to the reaction flask at the start of the experiment.
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Answer
Small pieces of glass or pumice stone serve to promote even heating and prevent bumping, which can lead to violent reactions. They provide nucleation sites for bubbles to form, allowing for a smoother boiling process.
Step 3
What was the colour of the solution of sodium dichromate(VI) before the reaction took place?
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The solution of sodium dichromate(VI) is typically orange before the reaction occurs due to the presence of dichromate ions.
Step 4
Why was the solution of ethanol and water added in small portions?
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The solution was added in small portions to control the reaction rate and to minimize the risk of a violent exothermic reaction that could occur if too much heat and product were generated at once.
Step 5
What colour was produced as the ethanol reacted with the sodium dichromate(VI)?
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As ethanol reacted with sodium dichromate(VI), the solution changed to green, indicating the reduction of chromium species.
Step 6
Why was it important to reflux the reaction mixture?
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Refluxing was important to bring the reaction to completion, ensuring that all reactants fully reacted and that the desired product was produced in higher yield.
Step 7
What was the main reason that water was not suitable for heating the flask during the distillation?
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Water was not suitable for heating the flask during distillation because the boiling point of ethanol is below 100 °C. Using water would not provide sufficient heat to distill the ethanol effectively.
Step 8
A dilution of 5–6% v/v of ethanoic acid (acetic acid) is used in food preservation and as a flavouring agent. What is the common name of this solution?
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The common name of the 5–6% v/v solution of ethanoic acid is vinegar, which is widely used for food preservation and seasoning.
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