The other ion formed is cl−, the chloride ion. Hydrochloric acid can therefore be used to prepare salts called chlorides, such as sodium chloride. Hydrochloric acid is a strong acid, since it is essentially completely dissociated in water. Monoprotic acids have one acid dissociation constant, ka, which indicates the level of dissociation in water. For a strong acid like hcl, the ka is large. Theoretical attempts to assign a ka to hcl have been made. When chloride salts such as Nacl are added to aqueous hcl they have practically no effect on ph, indicating that cl− is an exceedingly weak conjugate base and that hcl is fully dissociated in an aqueous solution. For intermediate to strong solutions of hydrochloric acid, the assumption that h+ molarity (a unit of concentration) equals hcl molarity is excellent, agreeing to four significant digits. Of the seven common strong mineral acids in chemistry, hydrochloric acid is the monoprotic acid least likely to undergo an interfering oxidation-reduction reaction. It is one of the least hazardous strong acids to handle; despite its acidity, it consists of the non-reactive and non-toxic chloride ion. Intermediate-strength hydrochloric acid solutions are quite stable upon storage, maintaining their concentrations over time. These attributes, plus the fact that it is available as a pure reagent, mean that hydrochloric acid makes an excellent acidifying reagent.