Ontario Operator-in-Training (OIT) Practice Exam

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When sodium hydroxide is added to water, what ion is released?

  1. Sodium ions

  2. Hydrogen ions

  3. Hydroxyl ions

  4. Chloride ions

The correct answer is: Hydroxyl ions

When sodium hydroxide (NaOH) is added to water, it undergoes dissociation, leading to the release of hydroxyl ions (OH-) into the solution. Sodium hydroxide is a strong base, and when it dissolves in water, it separates into sodium ions (Na+) and hydroxyl ions (OH-). The hydroxyl ions are responsible for the basic properties of the solution. This release of hydroxyl ions increases the pH of the water, making it more alkaline, which is a characteristic of basic solutions. Understanding the behavior of strong bases like sodium hydroxide in water is critical, as it plays a significant role in various chemical processes and reactions. The other ions mentioned do not accurately represent the ions that are released during this dissociation process, focusing instead on concepts that do not apply to the dissociation of sodium hydroxide.