In chemistry, understanding the acidity or alkalinity of an aqueous solution is critical for everything from industrial manufacturing to biological processes. The pH scale measures the concentration of hydrogen ions [H+], while the pOH scale measures hydroxide ions [OH-]. Because these concentrations can vary by orders of magnitude, a logarithmic scale is utilized to express them as manageable numbers.
Logarithmic pH Equations
pH = -log[H+]pOH = -log[OH-]
At 25°C, the relationship is always: pH + pOH = 14
How to Use This Calculator
- Select the known variable from your chemical data (e.g., pH, pOH, [H+], or [OH-]).
- Input the precise numerical value (using scientific notation if necessary for ion concentrations).
- Click Calculate to instantly find all three remaining values and determine if the solution is acidic, basic, or neutral.
Frequently Asked Questions (FAQ)
Why is the pH scale logarithmic?
Hydrogen ion concentrations in water span a massive range, from 1 M down to 0.00000000000001 M. Using a base-10 logarithmic scale compresses these extreme values into a simple 0 to 14 scale, making it much easier for chemists to read and compare.
What happens to pH when you dilute an acid?
Adding pure water to an acidic solution decreases the concentration of hydrogen ions. Because the scale is inversely logarithmic, a lower concentration of [H+] results in a higher pH value, shifting it closer to a neutral pH of 7.