Definition

Noun A measure of the acidity or alkalinity of a solution, expressed as the number of moles of hydrogen ions (H⁺) per cubic decimeter (liter) of that solution. It is the fundamental quantity from which the pH scale is derived.

Usage

This term is a specific scientific measurement used primarily in chemistry, biology, and environmental science to quantify the active acidity of an aqueous solution.

Examples

• The hydrogen ion concentration of pure water at 25°C is 1.0 × 10⁻⁷ mol/dm³.
• Scientists monitored the hydrogen ion concentration in the lake to assess the impact of acid rain.
• A high hydrogen ion concentration corresponds to a low pH value, indicating a strong acid.

Advanced Usage

• The term is central to the calculation of pH, where pH = -log₁₀[hydrogen ion concentration].
• In biochemistry, the precise hydrogen ion concentration is critical for enzyme activity and cellular function.

Variants and Related Words

• pH (noun): A logarithmic scale (typically from 0 to 14) used to specify the acidity or basicity of an aqueous solution, directly calculated from the hydrogen ion concentration.
• Molarity (noun): The concentration of a solution expressed as moles of solute per liter of solution. Hydrogen ion concentration is a specific type of molarity.
• Acidity (noun): The level of acid in a substance, closely related to its hydrogen ion concentration.

Synonyms

• [H⁺] (symbol, used in chemical notation)
• Proton concentration (in the context of aqueous chemistry, H⁺ is often referred to as a proton)

Notes

• The standard unit is moles per cubic decimeter (mol/dm³), which is equivalent to moles per liter (mol/L).
• "Hydrogen ion concentration" refers specifically to the concentration of free H⁺ ions, not hydrogen atoms or molecules (H₂).

Noun

1. the number of moles of hydrogen ions per cubic decimeter