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The table shows the boiling points of four primary alcohols and two secondary alcohols - Leaving Cert Chemistry - Question 8 - 2019
Question 8
The table shows the boiling points of four primary alcohols and two secondary alcohols. (a) (i) What is a secondary alcohol? (ii) On the same sheet of graph paper ... show full transcript
Worked Solution & Example Answer:The table shows the boiling points of four primary alcohols and two secondary alcohols - Leaving Cert Chemistry - Question 8 - 2019
Step 1
What is a secondary alcohol?
Answer
A secondary alcohol is an alcohol in which the hydroxyl (OH) group is attached to a carbon atom that is itself attached to two other carbon atoms. This means that in a secondary alcohol, the carbon with the OH group is connected to two additional carbon chains.
Step 2
On the same sheet of graph paper and using the same pair of axes, plot the boiling points of these alcohols against the number of carbon atoms present.
Answer
To plot the boiling points, use a graph with the x-axis representing the number of carbon atoms (from 1 to 4) and the y-axis as the boiling points in °C. Each alcohol's boiling point is marked according to its respective number of carbon atoms. For example, methanol (1C) at 64.7°C, ethanol (2C) at 78.4°C, propan-1-ol (3C) at 97.2°C, butan-1-ol (4C) at 117.5°C, butan-2-ol (4C) at 99.1°C.
Step 3
State and explain the trend in the boiling points of the four primary alcohols shown as their relative molecular masses increase.
Answer
The trend is that the boiling points of the primary alcohols increase as their relative molecular masses increase. This is primarily due to the increased van der Waals forces between the molecules. As the molecular mass increases, there are more electrons present, leading to stronger dispersion forces which require more energy (in the form of heat) to break during boiling.
Step 4
Predict the approximate boiling point of the next alcohol in the same series as propan-2-ol and butan-2-ol.
Answer
The next alcohol in the series after propan-2-ol and butan-2-ol would be pentan-2-ol. Given the rising trend of boiling points, one can predict that pentan-2-ol would have a boiling point around 120–125°C.
Step 5
Step 6
Step 7
Identify clearly which bonds in butan-2-ol are broken in this oxidation.
Answer
In the oxidation of butan-2-ol, the C-H bonds adjacent to the hydroxyl carbon (the carbon attached to the OH group) are broken. Specifically, the bond between the hydroxyl carbon and one of its attached hydrogen atoms is broken.
Step 8
Step 9
How many carbon atoms in a molecule of this ester are tetrahedrally bonded?
Answer
In the molecule of the ester formed from methanol and propanoic acid, there are a total of 4 carbon atoms that are tetrahedrally bonded. This includes the carbon in the hydroxyl group and the carbon in the carbonyl group.
Step 10