in a neutral solution the concentration of _____.

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24-01-2025

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In pure water, or a neutral solution, the concentration of hydrogen ions (H⁺) and hydroxide ions (OH⁻) are equal. This fundamental concept is crucial to understanding acidity, basicity, and the pH scale. Let's delve deeper into this equilibrium.

Understanding Hydrogen and Hydroxide Ions

Water (H₂O) is a special molecule. It can undergo self-ionization, meaning that it can spontaneously break apart into a hydrogen ion (H⁺) and a hydroxide ion (OH⁻). This process is represented by the following equilibrium reaction:

2H₂O ⇌ H₃O⁺ + OH⁻

While often simplified to:

H₂O ⇌ H⁺ + OH⁻

It's important to note that the hydrogen ion (H⁺) exists primarily as a hydronium ion (H₃O⁺) in aqueous solutions – a hydrogen ion bonded to a water molecule. However, for simplicity, we will use H⁺ in the rest of this explanation.

The Significance of Equilibrium in Neutral Solutions

The equilibrium shown above is dynamic. Water molecules constantly break apart and reform. In pure water at 25°C, the concentration of both H⁺ and OH⁻ ions is precisely 1 × 10⁻⁷ moles per liter (mol/L). This concentration is extremely small, reflecting the fact that water is mostly undissociated.

Because the concentrations of H⁺ and OH⁻ are equal in pure water, the solution is neutral. This equality is the defining characteristic of a neutral solution. Any deviation from this equality results in an acidic or basic solution.

The pH Scale and Neutrality

The pH scale is a logarithmic scale used to express the acidity or basicity of a solution. It is defined as the negative logarithm (base 10) of the hydrogen ion concentration:

pH = -log₁₀[H⁺]

In a neutral solution, where [H⁺] = 1 × 10⁻⁷ mol/L, the pH is calculated as:

pH = -log₁₀(1 × 10⁻⁷) = 7

Therefore, a neutral solution has a pH of 7. Solutions with a pH less than 7 are acidic, while solutions with a pH greater than 7 are basic (or alkaline).

Factors Affecting the Equilibrium

While pure water maintains a perfect balance of H⁺ and OH⁻ ions at 25°C, several factors can influence this equilibrium:

• Temperature: The self-ionization constant of water (Kw) increases with temperature. This means that at higher temperatures, the concentration of both H⁺ and OH⁻ increases, though they remain equal, resulting in a slightly lower pH for neutral water.

• Dissolved Substances: The addition of acids or bases will drastically alter the equilibrium, increasing the concentration of either H⁺ or OH⁻, respectively, and thus changing the pH of the solution.

Conclusion

In a neutral solution, the concentration of hydrogen ions (H⁺) and hydroxide ions (OH⁻) are equal. This equilibrium defines neutrality, with a pH of 7 at 25°C. Understanding this fundamental principle is essential for grasping concepts in chemistry related to acids, bases, and pH. Remember that this equilibrium can be affected by factors such as temperature and the presence of dissolved substances.