pH
/ pee-AYCH /
pH is a simple 0-to-14 score for how acidic or basic a liquid is. Low numbers mean acidic — think lemon juice or stomach acid; high numbers mean basic (also called alkaline) — think soap or bleach; and 7, right in the middle, is neutral, like pure water. Behind the number is one thing: how many hydrogen ions are crowded into the water. More of them, the more acidic, and the lower the pH.
Here's the part people miss: the scale is logarithmic, so each single step is a ten-fold change, not a one-step nudge. A pH of 4 isn't a little more acidic than 5 — it's ten times more, and pH 3 is a hundred times more than 5. That's why a small drop in the pH of the ocean or your blood is a much bigger deal than it sounds.
A common mix-up: pH doesn't measure how strong or dangerous a liquid feels, but the concentration of those hydrogen ions. And the scale isn't truly capped at 0 and 14 — very concentrated acids and bases can slip past both ends. For everyday life, though, 0 to 14 covers nearly everything you'll ever meet.
The pH equals the negative base-10 logarithm of the hydrogen-ion concentration — every drop of 1 in pH means ten times more hydrogen ions.
The name was coined in 1909 by Danish chemist Søren Sørensen while perfecting beer at the Carlsberg laboratory. The lowercase "p" is commonly read as the "power" of hydrogen, though Sørensen never recorded what he meant by it and its origin is still debated; the capital "H" is simply hydrogen's chemical symbol.