Question

The formula for hydronium ion is:
A.${H_2}{O^ + }$
B.${H_3}{O^ + }$
C.$O{H^ - }$
D.None of the above

Answer 1

We know that hydronium ions are a significant factor to observe chemical reactions taking place in aqueous solutions. They are formed only in the presence of acid in water or just pure water.

Complete step by step answer:
According to the Bronsted- Lowry concept of acids and bases, a substance that donates protons or hydronium ions is known as an acid, while a substance that has the ability to accept a proton and neutralize the acid is known as a base.
We know that a molecule of water can act as either a proton donor or as an acceptor. Depending on the conditions it could act either as a Bronsted acid or as a Bronsted base.
When an acid is present in aqueous solution, water acts as a base and accepts the protons that are released by the acid. As a result, a hydronium ion is formed. So, its chemical formula can be written as,
${H^ + } + {H_2}O \to {H_3}{O^ + }$

Thus, the correct answer is B.

Note:
We know that the molecular formula of hydronium ion is ${H_3}{O^ + }$. It is formed when a water molecule reacts with a hydrogen ion. A hydrogen ion does not have any electron, while the oxygen atom in the water molecule has two lone pairs. The oxygen atom shares a lone pair with the proton forming a coordinate bond. Thus, the oxygen atom in hydronium ion has three bond pairs and a lone pair. Thus, it has a tetrahedral geometry and the molecule is pyramidal in shape. In an aqueous solution, hydrogen atoms always exist as hydronium ions and are a measure of the pH of the solution.