The Hydroxyl ion (OH⁻) is characterized as a:

Appeared in: AIIMS CRE, SNO-2024

Explanation

The hydroxyl ion (OH⁻) is defined as a strong base because it has a very high affinity for protons (H⁺).
In an aqueous solution, it readily and rapidly accepts a proton to form a stable, neutral water molecule (H₂O), effectively removing H⁺ from the solution.
Substances that increase the concentration of OH⁻ in a solution, like sodium hydroxide (NaOH), are considered strong bases because they cause a significant increase in pH.

Option A: Incorrect. Acids are defined as proton donors. The hydroxyl ion is a proton acceptor, which is the definition of a base.
Option C: Incorrect. The hydroxyl ion (OH⁻) carries a negative electrical charge, making it an anion. Neutral molecules, by definition, have no net charge.
Option D: Incorrect. Strong acids, like hydrochloric acid (HCl), are substances that completely dissociate in water to donate a large number of protons (H⁺). The hydroxyl ion does the exact opposite; it removes H⁺ from the solution.

Visual 1: Diagram - The pH scale from 0 to 14. Label pH 7 as neutral, values below 7 as acidic (increasing H⁺ concentration), and values above 7 as alkaline/basic (increasing OH⁻ concentration). Show examples like gastric acid (pH ~1-2), blood (pH ~7.4), and drain cleaner (pH ~13-14).

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Chemical properties of the hydroxyl ion and its role in acid-base balance as background academic context rather than a clinical decision trigger.
Understanding that OH⁻ is a strong base is fundamental for nurses to grasp the principles of acid-base balance, which is critical for all physiological processes.
Nurses frequently interpret Arterial Blood Gas (ABG) results. A pH outside the narrow normal range of 7.35-7.45 indicates acidosis or alkalosis, prompting specific nursing interventions.
The administration of IV fluids, such as sodium bicarbonate, is directly related to these principles. Bicarbonate acts as a buffer to neutralize excess acid in cases of metabolic acidosis.

How to Approach the Question

First, recall the basic chemical definitions of acids and bases. Acids are proton (H⁺) donors, and bases are proton acceptors.
Next, analyze the hydroxyl ion (OH⁻). Its negative charge indicates it is an ion, not a neutral molecule, and suggests it will be attracted to a positive ion like H⁺.
Consider the chemical reaction: OH⁻ + H⁺ → H₂O. This shows the hydroxyl ion accepting a proton, which confirms it is a base.
Finally, determine its strength. The formation of water is a very stable and highly favorable reaction. This strong affinity for H⁺ means OH⁻ is a strong base, not a weak one.

Concept Tested & Keywords

Concept Tested: Chemical properties of the hydroxyl ion and its role in acid-base balance.
Stem keywords: Hydroxyl ion, OH⁻
Lead-in keywords: characterized as

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