Question

Which of the following is most soluble in water?
a.) n-butyl alcohol
b.) Iso-butyl alcohol
c.) Tertiary butyl alcohol
d.) None of these

Answer 1

Hint: Before attempting this question one must have prior knowledge about the solubility of alcohol in water, remember the factors due to which the solubility of alcohol increases in water, use this information to approach towards the solution to the problem.

Complete step by step solution: All the options given to us in the above question are isomeric alcohol which means when one or two molecules of alcohol have the same molecular formula but their structure is different from each other i.e. the position of OH group is different in each isomeric alcohol. The branching of these isomeric alcohols differ from each other.
Let us understand this by taking examples of given isomeric alcohols. First, n-butyl alcohol has an OH group attached with the first carbon atom. The structure of n-butyl is as follows:

Second, in iso-butyl alcohol has OH group attached to first carbon but a methyl group is attached to second carbon. The structure of iso-butyl is as follows:

Third, in tertiary butyl alcohol has OH and methyl groups both attached to the second carbon atom. The structure of tertiary butyl is as follows:

Now, in n butyl isomer the OH group is attached to one carbon which is then attached to one carbon atom, hence, it has one branch. So, it doesn’t have any methyl group while in iso-butyl OH group is attached to one carbon with methyl group attached to second carbon which means it has two branch (OH group is attached to one carbon atom which is then attached to another carbon atom which is attached to a methyl group forming two branches). In tertiary butyl, the OH group and methyl group are attached to the same 2nd carbon atom which means it has three branches. Thus, The solubility increases with increase in the number of branches because increase in branching increases the surface area of the non-polar hydrocarbon. Thus, the solubility increases which means that tertiary butyl isomer alcohol will be more soluble in water as compared n butyl and isobutyl.

Hence, Option C is correct.

Note: In the above question we came across the chemical compound tert-butyl alcohol which belongs to a tertiary alcohol which is an isobutane substituted at position 2 by hydroxyl group. The tert-butanol is used as a human xenobiotic metabolite on a medical basis. There are some properties that are shown by the tert-butanol such as it is a colorless liquid and oily with a sharp alcohol odor and it mixes in water and floats easily.