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