5ai)
The requirements needed for 2 molecules to form a hydrogen bond between them are:
one molecule must have a hydrogen atom bonded to either oxygen, nitrogen, or fluorine and
the second molecule must have a lone pair on an oxygen, nitrogen, or fluorine which can then interact with the hydrogen on the first molecule.
For example, hydrogen bonding can occur between 2 water molecules. The hydrogen atom bonded to oxygen in one water molecule can interact with the oxygen atom of the other water molecule.
5aii)
Carboxylic acids consist of a non polar hydrocarbon chain and a polar carboxylate group. Hydrogen bonding occurs between the carboxylate groups of acid molecules. Also Van Der Waals forces exists between the non polar hydrocarbon chains . Water molecules interact with each other through hydrogen bonding.
The first 4 members of the carboxylic acid series has short hydrocarbon chains and the predominant interactions between acid molecules is H bonding which is similar to the H bonding that exists between the water molecules hence they are soluble in water
For members of the the carbocxylic acid series with longer side chains, the predominant interaction between acid molecules is Van Der Waals forces due to the long hydrocarbon chain. This interaction is weaker than the hydrogen bonding that exists between water molecules, hence it is not favourable for the carboxylic acid to dissolve in water.
Side note: this question is surprisingly hard to answer. If anyone has a better answer please post it in the comments. chemguide.co.uk has a reasonably good explanation. in fact i can't find any other explanation on Google. My answer is mainly based on their explanation.
No comments:
Post a Comment