From RationalWiki
Jump to navigation Jump to search
Examples of the pH of some substances by OpenStax College.
Poetry of reality
Icon science.svg
We must know.
We will know.
A view from the
shoulders of giants.
Warning icon orange.svg This page contains too many unsourced statements and needs to be improved.

PH could use some help. Please research the article's assertions. Whatever is credible should be sourced, and what is not should be removed.

pH is a measure for the acidity or basicity of a substance dissolved in water.


The idea of pH was first introduced by the Danish chemist Søren Peder Lauritz Sørensen at the Carlsberg Laboratory in 1909. It was later revised to the modern concept of pH in 1924 to accommodate definitions and measurements in terms of electrochemical cells.

How it works[edit]

The scale assigns a number from 0-14.[note 1] to a water solution, depending on its acidity/basicity. Acidity/basicity is based on the concentration of hydrogen ions. 0 is the most acidic and 14 is the most basic. Pure water is considered neutral, with a pH of 7. Water exposed to air becomes mildly acidic, due to absorbing CO2 from the atmosphere. The pH scale is a logarithmic scale.[note 2] Therefore, a decrease in pH from 5.0 to 4.0 is equal to a ten-fold increase in the concentration of hydrogen ions (more precisely protons).


0-1 — hydrochloric acid (HCl), battery acid

2-3 — soda, lemon juice, vinegar

4-5 — lysosomes, black coffee

6-7 — milk, saliva, pure water

8-9 — sea water, baking soda

10-11 — ammonia (NH3)

11-13 — bleach (NaOCl)

14 — liquid drain cleaner (NaOH)


See also: pH woo

pH woo has to do with claiming that changing the pH balance of your body will miraculously and suddenly cause your health to improve. It is totally correct. [citation NOT needed]

Works cited[edit]


  1. The pH of a solution can be negative or greater than 14.
  2. In a pH 1 solution 1 molecule of solute in 101 (ie 1 in 10) have dissociated into a hydrogen ion and anion (carbonate in the CO2 example). In a pH 14 solution 1 in 1014 have dissociated (1 in 100 million million), and in pure water at pH 7 one molecule in 107 have dissociated (1 in 10 million).