1. In CH3 – NH2 , the +l effect of methyl group increases the electron density around N atom and it increases the electron releasing tendency of the molecule. In C6H5 – NH2 the resonance effect causes delocalisation of lone pair over the ring and thereby decreases its basic strength. Since aniline is less basic than methylamine, its pKb value is greater than that of CH3NH2 .
2. Solubility of ethylamine in water is attributed to its ability to form hydrogen bonds with water molecules. In aniline the non-polar hydrocarbon part (the ring skeleton) is relatively larger and therefore, has no interactions with polar water molecules. It also decreases the tendency of hydrogen bonding with water molecules. Hence, aniline is not soluble in water.
