Question

The strongest base among the following is:
A: Amide ion
B: Hydroxide ion
C: Trimethylamine
D: Ammonia
E: Aniline

Answer 1

A base refers to a substance which in water solution tends to be slippery to the touch, bitter in taste and changes the colour of indicators (i.e., turns the red litmus paper to blue). Base reacts with the acids in order to form salts.

Complete Step by step answer: A strong base refers to a base that completely dissociates in an aqueous solution. Strong base ionize in water and yield one or more hydroxide ions (i.e. $O{H^ - }$) per molecule of the base. The basic nature of the species is inversely proportional to the stability of the species ion. Let us discuss each one of the bases given in the options.
Option A: $N{H_2}^ -$(amide ion) is the least stable species ion. Thus, amide ion is the strongest base. From the periodic table, the electronegativity of Nitrogen is 3. Amide has two pairs of nonbonding electrons which leads to more electron-electron repulsion. Thus, nitrogen can easily donate the extra electron and thus, $N{H_2}^ -$is a strong base.
Option B: From periodic table, electronegativity of oxygen is 3.5 (greater than that of nitrogen). Hydroxide ions ($O{H^ - }$) also possess an extra lone pair of electrons. In this case, Oxygen can hold this extra electron much more tightly in comparison to nitrogen. Thus, hydroxide ion is a weaker base than amide ion.
Option C: The three methyl groups surrounding the amine nitrogen in Trimethylamine obstruct the protonation mechanism due to which Trimethylamine is a weaker base.
Option D: Ammonia does not dissociate into ions completely when dissolved in water which makes it a weak base.
Option E: In aniline, the lone pair of electrons on nitrogen are occupied in resonance, so it is not available for donation thereby making aniline a weaker base.

As a result, the correct answer is Option A i.e. The strongest base is amide ion.

Note: Base strength of any species is its capability to accept the ${H^ + }$ from another species. Greater the ability of any species to accept ${H^ + }$ from another species, the greater is its base strength. There are certain other measurements for finding out the basic strength of bases such as its electron donating capacity.