Which is the stronger base in water, NH2- or -OH? a) NH2-, because the negative charge is delocalized making the nitrogen more willing to accept a proton. b) NH2-, because the nitrogen is less electronegative and cant hold the negative charge as well as oxygen c) -OH, because the negative charge is delocalize making the oxygen more willing to accept a proton. d) -OH, because oxygen is less electronegative and cant hold the negative charge as well as nitrogen. e) -OH, because hydroxide is the strongest base possible
The Correct Answer and Explanation is:
Correct answer: (b) NH₂⁻, because the nitrogen is less electronegative and can’t hold the negative charge as well as oxygen.
Explanation:
In aqueous solution (water), basic strength depends on the ability of a species to accept a proton (H⁺). The stronger the base, the more readily it will accept a proton.
Both the amide ion (NH₂⁻) and the hydroxide ion (OH⁻) are negatively charged, meaning they both have a pair of electrons available to accept a proton. However, their basicity is influenced by the electronegativity of the atom bearing the negative charge.
Oxygen is more electronegative than nitrogen. This means that oxygen holds onto its electrons more tightly and stabilizes the negative charge more effectively than nitrogen. Because nitrogen is less electronegative, it does not stabilize the negative charge as well. As a result, the negative charge on NH₂⁻ is more “available” to grab a proton. This makes NH₂⁻ a much stronger base than OH⁻ in the gas phase and conceptually in basicity trends.
However, in water, the solvent plays a role too. Water can stabilize ions through hydrogen bonding and solvation. Even though NH₂⁻ is the stronger base, it is so reactive in water that it will immediately grab a proton from a water molecule to form ammonia (NH₃) and OH⁻. Therefore, NH₂⁻ cannot exist freely in water for long.
But the question is asking which is the stronger base in water, and in terms of intrinsic basicity (how strongly a species wants to accept a proton), NH₂⁻ is stronger than OH⁻ because nitrogen’s lower electronegativity makes it less capable of holding the negative charge. This drives NH₂⁻ to accept a proton more eagerly than OH⁻.
Thus, option (b) is the correct and most scientifically accurate answer.
