Final answer:
The pH scale is a measure of the hydrogen ion concentration in a solution and by inference also the hydroxide ion concentration, with values ranging from 0 to 14 to indicate acidity or basicity. It operates on a logarithmic scale where each pH unit reflects a tenfold difference in hydrogen ion concentration.
Step-by-step explanation:
The statement that the pH scale indicates the relative concentrations of hydrogen and hydroxyl ions in a solution is true. The pH scale effectively measures the concentration of hydrogen ions (H⁺) and indirectly reflects the concentration of hydroxide ions (OH⁻) in aqueous solutions due to the constant product of their concentrations at a given temperature (known as the ion product of water, or Kw). Therefore, if a solution is acidic, it has a greater concentration of hydrogen ions than hydroxide ions, and vice versa for a basic solution. The scale ranges from 0 to 14, where a pH level below 7 indicates acidity (higher concentration of H⁺), a pH of 7 indicates neutrality (equal concentrations of H⁺ and OH⁻), and a pH above 7 indicates basicity (lower concentration of H⁺).
The concept of pH is a log scale based on the concentration of hydrogen ions and is defined as the negative logarithm of the hydrogen ion concentration. This means that each unit change in pH corresponds to a tenfold change in hydrogen ion concentration. For example, a solution with a pH of 4 has a ten times higher concentration of hydrogen ions than a solution with a pH of 5.