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A student used the apparatus shown in the diagram to prepare and collect a number of test tubes of ethene gas - Leaving Cert Chemistry - Question 3 - 2011
Question 3
A student used the apparatus shown in the diagram to prepare and collect a number of test tubes of ethene gas. (i) Identify liquid X and solid Y and write an equati... show full transcript
Worked Solution & Example Answer:A student used the apparatus shown in the diagram to prepare and collect a number of test tubes of ethene gas - Leaving Cert Chemistry - Question 3 - 2011
Step 1
Step 2
The glass wool was used to hold liquid X at the bottom of the horizontal test tube. In setting up the apparatus, why is it preferable to put liquid X in the test tube before the glass wool?
Answer
It is preferable to place liquid X in the test tube before the glass wool to prevent the occurrence of a 'suck-back' effect. This ensures that enough of the liquid can soak up through the glass wool, avoiding any backflow that may cause contamination or hazards.
Step 3
Why were the first few test tubes of gas collected not used? Why was the delivery tube removed from the water when heating was stopped?
Answer
The first few test tubes of gas collected were likely not used because they contained impurities or unreacted gases. The delivery tube was removed to prevent any backflow of water into the apparatus when heating was stopped, which could lead to potential hazards.
Step 4
What did the student observe when a few drops of a solution of bromine in 1,1,1-trichloroethane was shaken in a test tube with ethene gas? What conclusion could be drawn from this observation? Name and give the use of this type of reaction.
Answer
The student would observe that the bromine solution decolorized, indicating that ethene was present due to its unsaturated nature. The conclusion drawn is that ethene undergoes an addition reaction with bromine, confirming its unsaturation. This type of reaction is useful in testing for alkenes.
Step 5
What did the student observe when a few drops of a solution of potassium manganate(VII) solutions was shaken in a test tube of ethene gas? Name this product.
Answer
The student would observe that the purple color of potassium manganate(VII) would disappear, indicating a reaction with ethene. The product formed is 1,2-dibromoethane, denoted by (C2HBr).
Step 6
What is meant by catalytic cracking? In carrying out this experiment, what solid would you use as a catalyst?
Answer
Catalytic cracking refers to the process of breaking down larger hydrocarbon molecules into smaller, more useful ones using a catalyst. In this experiment, a solid catalyst like porcelain or silica-alumina would be used.
Step 7