Photo AI
Answer any two of the parts (a), (b) and (c) - Leaving Cert Chemistry - Question 10 - 2015
Question 10
Answer any two of the parts (a), (b) and (c). (a) Distinguish between saturated and unsaturated hydrocarbons. Describe how you would test a given hydrocarbon for un... show full transcript
Worked Solution & Example Answer:Answer any two of the parts (a), (b) and (c) - Leaving Cert Chemistry - Question 10 - 2015
Step 1
Distinguish between saturated and unsaturated hydrocarbons.
Answer
Saturated hydrocarbons contain only single carbon-carbon bonds and have the maximum number of hydrogen atoms attached to the carbon skeleton. In contrast, unsaturated hydrocarbons contain at least one double or triple carbon-carbon bond, which reduces the number of hydrogen atoms that can be attached. For example, ethane (C2H6) is a saturated hydrocarbon, while ethene (C2H4) is unsaturated due to the presence of a double bond.
Step 2
Describe how you would test a given hydrocarbon for unsaturation.
Answer
To test a hydrocarbon for unsaturation, you could use a bromine (Br2) solution. Add a few drops of bromine water to the hydrocarbon in a test tube. If the solution decolorizes, this indicates the presence of unsaturation in the hydrocarbon, as the bromine reacts with the double or triple bonds. If no color change occurs, the hydrocarbon is saturated.
Step 3
Step 4
Step 5
Explain whether or not the Kekulé structure correctly describes (ii) the distribution of the pi-electrons in benzene.
Answer
The Kekulé structure does not accurately describe the distribution of pi-electrons in benzene. In reality, the pi-electrons are delocalized over the entire ring structure rather than localized between specific carbon atoms. This delocalization leads to increased stability of benzene compared to what the Kekulé structure suggests.
Step 6
Give one piece of experimental evidence in support of your explanation to part (ii).
Answer
One piece of experimental evidence is the observation of benzene's bond lengths. All carbon-carbon bonds in benzene are of equal length (approximately 1.39 Å), which is intermediate between single and double bonds, indicating the delocalization of electrons. This supports the idea that electrons are not localized as described by the Kekulé structure.