On the pH scale, numbers less than 7 indicate acidity, while numbers greater than 7 indicate alkalinity or basicity/Acids_and_Bases/Acids_and_Bases_in_Aqueous_Solutions/The_pH_Scale). A pH of 7 is considered neutral/Acids_and_Bases/Acids_and_Bases_in_Aqueous_Solutions/The_pH_Scale). The pH scale is logarithmic, meaning that a change of 1 pH unit corresponds to a ten-fold change in hydrogen ion concentration/Acids_and_Bases/Acids_and_Bases_in_Aqueous_Solutions/The_pH_Scale). For example, a solution with a pH of 5 is ten times more acidic than a solution with a pH of 6. Similarly, a solution with a pH of 3 is one hundred times more acidic than a solution with a pH of 5/Acids_and_Bases/Acids_and_Bases_in_Aqueous_Solutions/The_pH_Scale). The pH range is commonly given as 0 to 14, but a pH value can be less than 0 for very concentrated strong acids or greater than 14 for very concentrated strong bases.