Solubility of Amines in Water

Amines are organic compounds that have a nitrogen atom with a lone pair of electrons. They can be classified as primary, secondary, or tertiary, depending on the number of alkyl groups attached to the nitrogen atom. The solubility of amines in water depends on their molecular structure.

Factors Affecting Solubility

1. Hydrogen Bonding: Amines can form hydrogen bonds with water molecules. Primary amines can form two hydrogen bonds, secondary amines can form one hydrogen bond, and tertiary amines cannot form hydrogen bonds.

2. Molecule Size: Smaller molecules are more soluble in water than larger molecules.

3. Polarity: Polar molecules are more soluble in water than nonpolar molecules.

Solubility Order of Amines

Based on the above factors, we can predict the order of solubility of amines in water as follows:

1. Primary amines > Secondary amines > Tertiary amines
2. Smaller molecules > Larger molecules
3. Polar molecules > Nonpolar molecules

Answer Explanation

Now, let's look at the given options and determine the most soluble amine in water.

a) (CH3CH2CH2)2NH - This is a tertiary amine, so it cannot form hydrogen bonds with water. It is also a larger molecule, which makes it less soluble in water.

b) Ethylamine - This is a primary amine, so it can form two hydrogen bonds with water. It is also a smaller molecule than option (a), which makes it more soluble in water.

c) Pyrrolidine - This is a secondary amine, so it can form one hydrogen bond with water. It is also a smaller molecule than option (a), but larger than option (b), which makes its solubility in water less than option (b).

d) (CH3CH3)3N - This is a tertiary amine, so it cannot form hydrogen bonds with water. It is also a larger molecule than option (a) and (c), which makes it the least soluble amine in water.

As a result, the correct answer is option (b), Ethylamine, because of its ability to form two hydrogen bonds with water, its smaller molecule size, and its primary amine structure.