Step 1: Understanding the Concept:
The pH scale is a logarithmic scale used in chemistry to specify the acidity or basicity (alkalinity) of an aqueous solution.
Step 2: Key Formula or Approach:
The approach relies on the autoionization of water, where the concentration of hydrogen ions \( [H^+] \) equals the concentration of hydroxide ions \( [OH^-] \).
The formula for pH is \( \text{pH} = -\log_{10}[H^+] \).
Step 3: Detailed Explanation:
The standard pH scale typically ranges from 0 to 14 at room temperature \( (25^\circ\text{C}) \).
A pH value less than 7 indicates an acidic solution, while a pH value greater than 7 indicates a basic solution.
Pure water undergoes autoionization to produce equal concentrations of hydrogen ions \( (\text{H}^+) \) and hydroxide ions \( (\text{OH}^-) \), both being \( 1.0 \times 10^{-7} \) M at \( 25^\circ\text{C} \).
Using the formula, \( \text{pH} = -\log_{10}(1.0 \times 10^{-7}) = 7 \).
Because these acidic and basic ion concentrations are perfectly balanced, pure water is chemically neutral.
Step 4: Final Answer:
The pH value of pure water at room temperature is exactly 7.