Chemists use the pH scale for measuring acidity or alkalinity of a substance. The formula is pH = log (H +) where H + is the concentration of hydrogen ions in moles per liter of the substance. On this scale, 7 is neutral, below 7 is acidic, and above 7 is alkaline. For healthy individuals, human saliva has an average pH of 6.4. What is the typical concentration of hydrogen ions in human saliva