Here's why:
* pH = -log[H+] where [H+] is the hydrogen ion concentration in moles per liter (M).
* The scale is logarithmic, meaning each whole number change in pH represents a tenfold change in hydrogen ion concentration.
* A lower pH indicates a higher concentration of hydrogen ions, making the solution more acidic.
* A higher pH indicates a lower concentration of hydrogen ions, making the solution more basic (alkaline).
While pH doesn't directly give the exact number of ions, knowing the pH allows you to calculate the hydrogen ion concentration:
* [H+] = 10^-pH
Example:
* A solution with a pH of 3 has a hydrogen ion concentration of 10^-3 M (or 0.001 M).
* A solution with a pH of 10 has a hydrogen ion concentration of 10^-10 M.
Important note:
* The relationship between pH and hydroxide ions is inverse. A higher pH indicates a lower concentration of hydroxide ions and vice versa.
* The product of hydrogen ion concentration and hydroxide ion concentration is constant (Kw = 10^-14 at 25°C).
Therefore, knowing the pH of a solution lets you determine the relative concentration of hydrogen ions and hydroxide ions, but it doesn't provide the exact number of ions present.
