A group of students prepared ethanol (C2H5OH) by slowly adding a mixture of ethanol (C2H5OH) and an oxidising agent in water, to hot aqueous sulfuric acid - Leaving Cert Chemistry - Question 1 - 2005
Question 1
A group of students prepared ethanol (C2H5OH) by slowly adding a mixture of ethanol (C2H5OH) and an oxidising agent in water, to hot aqueous sulfuric acid. The appar... show full transcript
Worked Solution & Example Answer:A group of students prepared ethanol (C2H5OH) by slowly adding a mixture of ethanol (C2H5OH) and an oxidising agent in water, to hot aqueous sulfuric acid - Leaving Cert Chemistry - Question 1 - 2005
Step 1
Identify this solid and state its purpose.
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Answer
The solid material is likely to be pumice stones or boiling chips. Their purpose is to prevent bumping during the boiling process.
Step 2
Identify a suitable oxidising agent for this preparation.
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Answer
A suitable oxidising agent for this preparation is sodium dichromate (Na2Cr2O7) or potassium permanganate (KMnO4).
Step 3
What is the colour of the mixture in the dropping funnel at the start?
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The colour of the mixture in the dropping funnel at the start is generally yellow if sodium dichromate is used.
Step 4
What is the colour of the mixture in the reaction flask as the reaction proceeds?
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The colour of the mixture in the reaction flask changes to green as the permanganate is reduced, or it may appear colourless if sodium dichromate is used.
Step 5
Why is it important to distill off the ethanol as it is produced?
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It is important to distill off the ethanol as it is produced to prevent excess oxidation of the product and to avoid the formation of ethanoic acid due to the volatility of ethanol.
Step 6
Why is it not necessary to keep heating the reaction flask during the addition?
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It is not necessary to keep heating the reaction flask during the addition because the reaction is exothermic, meaning it generates heat.
Step 7
Why is the receiving vessel cooled in ice-water?
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The receiving vessel is cooled in ice-water to condense the ethanol vapour efficiently and to maintain a low temperature to prevent loss of product.
Step 8
What colour is the solid produced when a mixture containing a few drops of Fehling’s solutions (No 1 and No 2) and ethanol is heated?
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The solid produced is brick red in colour, indicating the formation of copper(I) oxide.
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