Hydronium (H3O+), Hydroxide (OH-), pH, and Molarity.
pH is often measured on a scale of 0 to 14 and is a measure of the concentration of hydronium ions versus hydroxide ions. pHs of 7.00 are regarded as neutral because they are neither acidic nor alkaline. Below 7.00 would be considered acidic and as the pH moves closer to 0.00 the stronger the acid becomes. Acids tend to have a higher concentration of hydronium ions than hydroxide ions. As the pH moves above 7.00 the solution would be considered alkaline or basic, and as it moves closer to 14.00 the base becomes stronger. Bases tend to have a higher concentration of hydroxide ions than hydronium ions. These ratios are also reflected by the molarity of a solution.
Molarity is a measure of the concentration of a solution and is defined as the number of moles of solute per liter of solution (moles solute/moles solvent). In the context of hydronium (H3O+), hydroxide (OH-), and pH, molarity is directly related to the concentration of these ions in an aqueous solution.
Hydronium ions (H3O+) are formed when a water molecule (H2O) combines with a hydrogen ion (H+) that is given off by an acid. The concentration of hydronium ions in a solution is represented by the molarity of the hydronium ion. The higher molarity of an acid indicates a more acidic solution and a lower pH, as there are more hydronium ions present. Thus, an acid with a molarity of 1.0 M will have more hydronium ions than an acid with a molarity of 0.5 M.
Similarly, hydroxide ions (OH-) are formed when water and bases dissociate. The concentration of hydroxide ions in a solution is also represented by its molarity. The higher molarity of a base (alkaline solution) indicates a more alkaline solution and a higher pH, as there are more hydroxide ions present. Thus, an alkaline solution with a molarity of 1.0 M will have more hydroxide ions than an alkaline solution with a molarity of 0.5 M.