Final answer:
The pH scale measures the acidity or basicity of a solution, which is determined by the concentration of H+ ions. The pH value is the negative log of the H+ concentration, with lower pH values being more acidic and higher values being more basic.
Step-by-step explanation:
The Relationship between Hydrogen Ions (H+) and pH
The pH scale is a measure of the acidity or basicity of a solution, which is determined by the concentration of hydrogen ions (H+). In simple terms, the pH value is the negative logarithm (base 10) of the hydrogen ion concentration. When the hydrogen ion concentration increases (more acidic), the pH value decreases; conversely, when the hydrogen ion concentration decreases (more basic), the pH value increases.
A neutral solution, such as pure water, has a pH of 7. This indicates it has a hydrogen ion concentration of 1 × 10-7 moles per liter. Acids are substances that provide hydrogen ions and lower the pH value, while bases provide hydroxide ions (OH-) which raise the pH value by combining with hydrogen ions to form water.
A solution with a pH less than 7 is considered acidic, and a solution with a pH greater than 7 is considered basic. For example, hydrochloric acid has a high concentration of H+ ions and a low pH, while sodium hydroxide has a high concentration of OH- ions and a high pH.