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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 - 2001
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 - 2001
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 place liquid X at the bottom of the test tube before the glass wool?
Answer
Placing liquid X (ethanol) at the bottom allows for better absorption and less liquid remaining on top of the glass wool. This setup ensures that there is sufficient contact between the heat source and liquid X, facilitating efficient heating and reaction.
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 may contain air and impurities from the reaction, which could contaminate the ethene collected. The delivery tube was removed from the water to prevent backflow of water into the reaction mixture, which could disrupt the process.
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 of ethene gas? What conclusion could be drawn from this observation? Name and give the use of this type of reaction.
Answer
The bromine solution would decolorize, indicating a reaction due to the presence of unsaturation (double or triple bond) in ethene. This conclusion demonstrates that ethene is an alkene, which can undergo addition reactions. This type of reaction is used in organic chemistry for the identification of unsaturated hydrocarbons.
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? One of the products of this reaction has the formula (CH2Br)2. Name this product.
Answer
The potassium manganate(VII) solution would decolorize as it reacts with ethene, indicating the formation of a product. The product formed is 1,2-dibromoethane, with the formula (C2H4Br2).
Step 6
The above apparatus can also be used to demonstrate catalytic cracking using liquid paraffin in place of liquid X. What is meant by catalytic cracking? In carrying out this reaction, what solid would you use as a catalyst?
Answer
Catalytic cracking is a process used to break down large hydrocarbons into smaller, more useful products by using heat and a catalyst. A common solid catalyst for this reaction is porcelain or silica-alumina.
Step 7
When a sample of liquid paraffin was cracked, the mixture of products was found to contain a number of isomeric compounds of the formula C4H8. Draw the structure and give the IUPAC name of two of these compounds.
Answer
Two isomeric compounds of C4H8 can be represented as:
-
But-1-ene:
H2C=CH-CH2-CH3
-
2-Methylpropene (or isobutylene):
CH2=C(CH3)-CH3
These structures demonstrate the different arrangements of carbon and hydrogen atoms within the same molecular formula.