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Question Video: Determining How Water Can Be Defined by Lewis Theory Chemistry

Water can react with ammonia and hydrogen chloride according to the following chemical equations. H₂O + NH₃ ⟶ NH₄⁺ + OH⁻. H₂O + HCl ⟶ H₃O⁺ + Cl⁻. According to these equations, how can water be defined in terms of Lewis’s theory?

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Video Transcript

Water can react with ammonia and hydrogen chloride according to the following chemical equations. H2O plus NH3 produces NH41+ plus OH1−. H2O plus HCl produces H3O1+ plus Cl1−. According to these equations, how can water be defined in terms of Lewis’s theory? (A) A Lewis acid, (B) a Lewis base, or (C) both a Lewis acid and a Lewis base.

To answer this question, we must consider how water is defined in regards to the Lewis acid–base theory. To do this, we must understand the definitions for a Lewis acid and a Lewis base. A Lewis acid is a substance that can accept a lone pair of electrons, forming a bond, while a Lewis base can donate an electron pair. So we must identify whether water in these chemical reactions is accepting or donating a lone pair of electrons or if it is doing both.

Let’s have a closer look at these reactions using Lewis dot structures to determine the behavior of water. In this first reaction, water reacts with ammonia by accepting a lone pair of electrons to form the hydroxide ion and the ammonium ion. Because water accepted a lone pair of electrons in this reaction, it can be described as a Lewis acid.

Let’s have a look at the second reaction between water and hydrogen chloride. In this reaction, water donates a lone pair of electrons as it bonds with a hydrogen ion to form the hydronium ion and the chloride ion. Because water has donated a lone pair of electrons in this reaction, it is behaving as a Lewis base.

Therefore, water can be classified as an amphoteric species, which means it can act as an acid in some circumstances and as a base in others. Therefore, according to the equations, water can be defined in terms of Lewis’s theory as answer choice (C), both a Lewis acid and a Lewis base.

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