In relation to the pH scale, a lower pH number corresponds to what type of substance?

A lower pH number corresponds to a stronger acid on the pH scale. The pH scale ranges from 0 to 14, where values below 7 represent acidity, values at 7 represent neutrality, and values above 7 indicate alkalinity or basicity. Specifically, each whole number change on the pH scale represents a tenfold change in hydrogen ion concentration. Consequently, a solution with a pH of 4 is ten times more acidic than one with a pH of 5, and a solution with a pH of 3 is ten times more acidic than one with a pH of 4, reinforcing that as the pH decreases, the acidity increases. This is why a lower pH number indicates a stronger acid rather than a weaker acid, a neutral substance, or a stronger base.