Question

Consider the following statements and select the correct option: Statement-I : Solubility of aliphatic amines in water decreases with increase in molecular mass. Statement-II : On increase in size of the hydrophobic alkyl part, higher amines become insoluble in water.

• A. Both Statement-I and Statement-II are correct and Statement-II justifies Statement-I.
• B. Both Statement-I and Statement-II are incorrect.
• C. Statement-I is correct but Statement-II is incorrect.
• D. Statement-I is incorrect but Statement-II is correct.

Hint:

Solubility trend of aliphatic amines in water: \[ \text{Methylamine} \gt \text{Ethylamine} \gt \text{Propylamine} \gt \text{Butylamine} \] Increasing alkyl chain length increases hydrophobic character and decreases solubility.

Answer 1

The Correct Option is A

Concept: Lower aliphatic amines are soluble in water because they form hydrogen bonds with water molecules. As the alkyl chain length increases, the hydrophobic character increases and solubility decreases.

Step 1: Analyze Statement-I. Aliphatic amines can form hydrogen bonds with water. However, as molecular mass increases, the non-polar alkyl part becomes larger and dominates over the polar amino group. Therefore, solubility decreases with increase in molecular mass. \[\begin{aligned} \text{Statement-I is Correct} \end{aligned}\]

Step 2: Analyze Statement-II. The alkyl group is hydrophobic in nature. As its size increases, the hydrophobic character increases and the molecule becomes less soluble in water. Hence higher amines become insoluble in water. \[\begin{aligned} \text{Statement-II is Correct} \end{aligned}\]

Step 3: Check whether Statement-II explains Statement-I. Statement-II gives the exact reason for the decrease in solubility mentioned in Statement-I. \[\begin{aligned} \boxed{\text{Both statements are correct and Statement-II justifies Statement-I}} \end{aligned}\] Hence, option \(\mathbf{(A)}\) is correct.