HI is an Arrhenius acid because
- A) it is a polar molecule.
- B) it can dissolve in water.
- C) it produces hydronium ions in solution.
- D) it produces hydroxide ions in solution.
The correct answer and explanation is :
The correct answer is: C) it produces hydronium ions in solution.
Explanation:
An Arrhenius acid is defined as a substance that increases the concentration of hydronium ions (H₃O⁺) or simply hydrogen ions (H⁺) in aqueous solution. When hydroiodic acid (HI) dissolves in water, it dissociates completely into H⁺ ions and I⁻ ions:
[
\text{HI} \, (aq) \rightarrow \text{H}^+ \, (aq) + \text{I}^- \, (aq)
]
The free H⁺ ions immediately associate with water molecules to form hydronium ions (H₃O⁺):
[
\text{H}^+ + \text{H}_2\text{O} \rightarrow \text{H}_3\text{O}^+
]
Thus, the main characteristic that qualifies HI as an Arrhenius acid is that it produces hydronium ions when dissolved in water.
Now, let’s look at why the other options are incorrect:
- A) it is a polar molecule: While HI is indeed polar (due to the difference in electronegativity between hydrogen and iodine), simply being polar does not necessarily make a molecule an acid. Many polar molecules, like sugar, are not acids.
- B) it can dissolve in water: Solubility alone does not make a substance an Arrhenius acid. Some substances dissolve in water without releasing H⁺ ions (for example, salt, NaCl).
- D) it produces hydroxide ions in solution: This describes an Arrhenius base, not an acid. Bases produce OH⁻ ions, not H₃O⁺ ions.
HI is considered a strong acid because it dissociates almost completely in water, making it very effective at increasing the H₃O⁺ concentration. This property is essential in acid-base chemistry, especially in reactions where the acidity of a solution influences the course of the reaction.
In conclusion, HI is an Arrhenius acid because it increases hydronium ion concentration in water, fitting perfectly into the Arrhenius definition of an acid.