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Trends in physical properties of alcohols
Trends are never easy to remember. But if we understand the reason behind the trends, we can make our work simpler.
Solubility is an important physical property to study in this chapter.
Before we come around to talk about the trend in solubility, we should first look at the structure of alcohol.
You may well remember the structure of a soap molecule. Are you thinking what has soap has to do with alcohols? Well, alcohols have a structure similar to that of a soap molecule. How? Let's see.
Soap has a polar head and non polar tail, the polar head is hydrophilic and the non-polar tail is hydrophobic

The structure of an alcohol can be described in a similar manner. The oxygen atom in the hydroxy group, makes alcohols polar.
Similar to a soap molecule, the polar part can interact with the water molecules. The lower alcohols have a very short non-polar tail(-R, the alkyl group), and so, they are miscible in water. But as the length of the tail grows, the solubility of alcohol in water decreases.
Similar to a soap molecule, the polar part can interact with the water molecules. The lower alcohols have a very short non-polar tail(-R, the alkyl group), and so, they are miscible in water. But as the length of the tail grows, the solubility of alcohol in water decreases.



Let's look at the next physical property - Boiling point

If you study the bar diagram above, you will see that alcohols have a higher boiling point than alkanes of comparable molecular masses. This is because the alkanes are held together by weak van der Waals forces. But the molecules of alcohols engage in intermolecular hydrogen bonding, which greatly increases their boiling points.

Next, when you compare the boiling points of the homologous series, you will see a trend like this:

The boiling point increases with the increase in the size of the carbon chain. Why does this happen?
With the increase in the size of the carbon chain, intermolecular interactions(van der Waals and dipole-dipole) increase. As a result, more energy is required to overcome the intermolecular interaction, which ultimately increases the boiling point
Here are some questions you can attempt from this topic:-
Here are some questions you can attempt from this topic:-
Butane has a _______ boiling point to that of propanol.
Alcohols containing only up to ___________ carbon atoms are completely miscible with water.