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Examine the reaction scheme and answer the questions which follow - Leaving Cert Chemistry - Question 7 - 2005
Question 7
Examine the reaction scheme and answer the questions which follow. C₂H₅OH W → C₂H₆ X Y → C₂H₅Cl Z (a) Name the compound labelled Δ... show full transcript
Worked Solution & Example Answer:Examine the reaction scheme and answer the questions which follow - Leaving Cert Chemistry - Question 7 - 2005
Step 1
Step 2
For each of the conversions W, X and Z, classify it as an addition, an elimination or a substitution reaction.
Answer
W: This conversion is classified as an elimination reaction as it involves the removal of a water molecule to form an alkane from an alcohol. X: This conversion is classified as an addition reaction, as it involves the incorporation of a group into the molecule. Z: This conversion is classified as a substitution reaction since it involves the replacement of one functional group with another.
Step 3
Describe with the aid of a labelled diagram how the conversion W may be carried out in a school laboratory and how a sample of the product may be collected. How would you test this product to show that it is unsaturated?
Answer
To carry out the conversion W in a school laboratory, the following steps can be followed:
- Set up a horizontal test tube connected to a delivery tube. The tube should lead to a gas over water to collect the gaseous product.
- Heat the ethanol (C₂H₅OH) in the test tube using a Bunsen burner, ensuring to indicate the source of heating.
- Use aluminum oxide (Al₂O₃) as a catalyst to facilitate the elimination reaction.
- The product (C₂H₆) collected can be tested for unsaturation by using bromine water; if it decolorizes, it indicates that the product is unsaturated.
- Label the diagram with appropriate equipment such as the test tube, delivery tube, and collection container.
Step 4
The conversion labelled Z is known to occur by a free radical mechanism. State three clear pieces of experimental evidence which support this mechanism.
Answer
- The use of light to initiate the reaction supports the free radical mechanism, as light provides the energy required to break bonds and generate radicals.
- The presence of radical inhibitors, such as substances that prevent the formation of radicals, will slow down or stop the reaction, demonstrating the involvement of free radicals.
- Observations of secondary reactions that lead to the formation of side products consistent with radical intermediates indicate that a free radical mechanism is at play.