Final answer:
The pH scale indicates that a value of 7 represents a neutral solution, where the concentrations of H⁺ and OH⁻ ions are equal (1.0 × 10⁻⁷ M). The pH value is the negative logarithm of the hydrogen ion concentration, and the pH scale is logarithmic, meaning each whole number change represents a tenfold change in acidity or basicity.
Step-by-step explanation:
The pH Scale and Neutral Solutions
The value on the pH scale that indicates a neutral solution is 7. At this pH level, the concentrations of hydrogen ions (H⁺) and hydroxide ions (OH⁻) are equal, each being 1.0 × 10-7 M (molar). This equilibrium where [H⁺] equals [OH⁻] characterizes a neutral solution, such as pure water. The concept of pH is essentially the negative logarithm of the hydrogen ion concentration, which makes it a convenient measure of acidity or basicity. A pH less than 7 indicates an acidic solution with higher [H⁺], and a pH greater than 7 indicates a basic solution with lower [H⁺].
It's important to understand that the pH scale is logarithmic; therefore, a pH difference of 1 unit reflects a tenfold change in [H⁺] concentration. For example, a solution with a pH of 6 has ten times more [H⁺] than a solution with a pH of 7.
The pOH is another scale used alongside pH, where the pOH of a solution plus its pH always equals 14. Similar to pH, a pOH of 7 indicates a neutral solution, while a pOH lower than 7 corresponds to a basic solution, and a pOH higher than 7 corresponds to an acidic solution.