The chemistry terms pH and concentration are connected in several ways. The pH scale is a logarithmic scale that measures hydrogen ions in a solution. The concentration of hydrogen ions determines whether a solution will behave as an acid, base, or both. The properties of acids and bases are determined by pH and the concentration of the acid and base molecules in a solution. For example, the pH and concentration of hydrogen ions makes water act as both an acid and a base, but having more ions makes a solution acidic.

All solutions have a specific pH and are made with a solvent, usually water, and a solute, which dissolves easily in the chosen solvent. Using a logarithmic scale for pH helps keep the scale small while retaining the valuable information the pH scale represents. One connection between pH and the concentration of hydrogen ions is that together they allow the use of a logarithmic scale. The lower the pH number the more concentrated the hydrogen ions, because pH measures the negative log of hydrogen ion concentration, meaning 0.1 ion concentration is one on the pH scale and 0.001 is three.

Together, the pH and concentration determine predictable changes to the properties of any given acid or base solution. This can be shown by heating both a solvent dissolved within a solute, like salt water, and pure solvent to a boil. The temperature at which one solution begins to boil will be different, so the properties of transforming from liquid to gas has been changed by increasing the solute concentration. It is possible to increase the boiling temperature of a solution and decrease the freezing temperature of a solution. Adding a small amount of bicarbonate salt does this to water by increasing the base salt concentration and raising the pH number.

Another connection between pH and concentration is that both are calculated in a similar way. Solution concentration measures how much of a certain atom or molecule is present compared to the entire solution. The pH is a special concentration measurement that measures how many hydrogen ions are in a solution compared to everything else in the solution. Other concentration calculations do not use the pH scale. Instead they use a unit called Molarity, which is the amount of atoms or molecules available per liter of solvent.

The simplest connection between pH and concentration also exists because of the logarithmic scale used. They become linearly connected by a factor of ten and the pH changes by a factor of one when hydrogen ion concentration changes by a factor of ten. The normal relationship is said to be exponential and this connection helps avoid tedious equations involving higher levels of mathematics. This automatically changes the curved relationship to a linear relationship where simple math applies. The straight line makes predictions, relationships between different concentrations, and calculations easy to visualize.