Question

Which molecule is considered a base in the Lewis model, but not in the Brønsted-Lowry or Arrhenius model? PO43− NaOH NH3 Na2S

Answer 1

The answer for platoo users is D.

Answer 2

Answer: $NH_3$

Explanation: According to Arrhenius concept, a base is defined as a substance which donates hydroxide ions $(OH^-)$ when dissolved in water and an acid is defined as a substance which donates hydronium ions $(H_3O^+)$ in water.

According to the Bronsted Lowry conjugate acid-base theory, an acid is defined as a substance which donates protons and a base is defined as a substance which accepts protons.

According to the Lewis concept, an acid is defined as a substance that accepts electron pairs and base is defined as a substance which donates electron pairs.

Thus $NH_3$ is a lewis base as it contains a lone pair of electrons and thus can donate it.

$NH_3+H^+\rightarrow NH_4^+$