How does the number of hydrogen ions compare to the number of hydroxide ions?

Answer 1

In pure water, at standard conditions, the number of hydrogen ions (H⁺) is equal to the number of hydroxide ions (OH⁻). This balance occurs due to the self-ionization of water molecules:

H

2

O

⇌

H

OH

−

H

2

​

O⇌H

+OH

−

For every water molecule that dissociates, one hydrogen ion (H⁺) and one hydroxide ion (OH⁻) are produced. The concentration of hydrogen ions (H⁺) is often denoted as [H⁺], and the concentration of hydroxide ions (OH⁻) is denoted as [OH⁻]. In neutral water (pH 7), these concentrations are equal:

[H+]=[H−]=10−7  mol/L [H+ ]=[OH− ]=10−7 mol/L

This balance ensures that the solution remains neutral. However, in acidic solutions, the concentration of hydrogen ions (H⁺) is higher than that of hydroxide ions (OH⁻), while in basic solutions, the concentration of hydroxide ions (OH⁻) is higher than that of hydrogen ions (H⁺). The product of the hydrogen ion concentration and the hydroxide ion concentration is always

10−14 mol 2 / L210−14 mol2 /L2

at 25°C, known as the ion product of water.