Definition
pH is a numerical scale from 0 to 14 used to express the acidity or alkalinity of a water-based solution. A pH of 7 is neutral, values below 7 are acidic, and values above 7 are alkaline (basic). The scale is logarithmic, meaning each whole number represents a tenfold change in acidity or alkalinity.
Plain English
pH is a number that tells you how acidic or how alkaline a liquid is. Lower numbers mean more acidic, higher numbers mean more alkaline, and 7 sits in the middle as neutral.
Context Anchor
Seen in aircraft maintenance when checking liquids such as cleaning solutions, water contamination, battery-related fluids, or chemical treatments.
Derivation
pH comes from the Latin and French chemistry shorthand 'pondus hydrogenii' or 'potentia hydrogenii,' meaning the weight or power of hydrogen. It refers to the concentration of hydrogen ions in a solution — more hydrogen ions means more acidic, fewer means more alkaline. Knowing this helps explain why pH is really a measurement of hydrogen activity, not just a vague 'sourness' rating.
Why Pilots Care
Battery electrolyte, cleaning fluids, and aircraft wash products all have pH values that affect corrosion and material compatibility. Using a fluid with the wrong pH on aluminum skin or sensitive components can cause corrosion or damage.
Grounding Statement
A low Ph means the liquid is acidic, a high Ph means it is alkaline, and 7 means it is neutral.
Intuition Check
Do not read Ph as a random letter code. In this context it refers to the pH scale for acidity and alkalinity.
Example Sentence 1
The technician checked the pH of the lead-acid battery electrolyte to confirm it was within the acceptable acidic range.
Example Sentence 2
A single-Ph motor drives the standby vacuum pump.