Acidic and Basic
- A hydrogen atom in a hydrogen bond between two water molecules can shift from one to the other
- Hydrogen atom leaves electron behind and is transferred as a proton = hydrogen ion (H+)
- The molecule that lost the proton = hydroxide ion (OH−)
- The molecule with the extra proton = hydronium ion (H3O+), though it is often represented as “H+”
Water
- Water = state of dynamic equilibrium
- Water molecules dissociate at the same rate at which they are being reformed

- Changes in concentrations of H+ and OH− can change the pH of the environment
- Concentrations of H+ and OH− equal in pure water
- Adding acids/bases alters the concentrations of H+ and OH−
- The pH scale is used if a solution is acidic or basic
Acids and Bases
- Acid = increases the H+ concentration of a solution
- Base = reduces the H+ concentration of a solution
- Strong acids/bases dissociate completely in water
- Weak acids/bases release/accept back hydrogen ions, but can still shift the balance of H+ and OH− away from neutrality
The pH Scale
- The pH = negative logarithm of H+ concentration, written as pH = − log [H+]
- For a neutral aqueous solution, [H+] is 10−7, so pH = −(− 7) = 7

- Acidic solutions <7
- Basic solutions > 7
- Most biological fluids = 6 to 8

