pH Calculator
pH Calculator
Calculate pH, pOH, [H⁺], or [OH⁻] for a solution.
Enter the known value and select what you want to solve for.
Formulas: pH = -log[H⁺], pOH = -log[OH⁻], pH + pOH = 14
The Measure of Acidity: A Guide to the pH Calculator
The pH scale is a logarithmic scale used to specify the acidity or basicity of an aqueous (water-based) solution. It is one of the most common and important measurements in all of chemistry and biology. The term 'pH' stands for 'potential of hydrogen' and is a measure of the concentration of hydrogen ions [H⁺] in a solution. A higher concentration of H⁺ ions makes a solution more acidic, while a lower concentration makes it more basic (or alkaline). The pH scale typically ranges from 0 to 14, providing a simple and intuitive way to describe acidity.
This pH calculator is a versatile tool for students and scientists, allowing for easy conversion between pH, pOH, hydrogen ion concentration [H⁺], and hydroxide ion concentration [OH⁻]. Understanding the relationships between these four values is fundamental to acid-base chemistry. Whether you're determining the pH of a solution from a known concentration or calculating the ion concentration from a pH reading, this tool simplifies the logarithmic calculations involved.
The pH Scale and Its Formulas
The pH scale is a logarithmic scale, which means that each whole number change on the scale represents a tenfold change in acidity.
- A solution with a pH of 3 is 10 times more acidic than a solution with a pH of 4.
- A solution with a pH of 3 is 100 times more acidic than a solution with a pH of 5.
The key formulas that govern these relationships at 25°C are:
- Definition of pH:
pH = -log₁₀[H⁺] - Definition of pOH:
pOH = -log₁₀[OH⁻] - Relationship between pH and pOH:
pH + pOH = 14 - Ion Product of Water (Kw):
[H⁺] × [OH⁻] = 1 × 10⁻¹⁴
Acids, Bases, and Neutral Solutions
- Acidic Solution: Has a pH less than 7. In these solutions, the concentration of hydrogen ions [H⁺] is greater than the concentration of hydroxide ions [OH⁻].
- Neutral Solution: Has a pH of exactly 7. In a neutral solution, like pure water, the concentrations of [H⁺] and [OH⁻] are equal (1 × 10⁻⁷ M).
- Basic (or Alkaline) Solution: Has a pH greater than 7. In these solutions, the concentration of hydroxide ions [OH⁻] is greater than the concentration of hydrogen ions [H⁺].