pH : pH measures the concentration of hydrogen ions (H+H^+) in a solution, indicating its acidity or alkalinity.

pH=−log?10[H+]\text{pH} = -\log_{10}[\text{H}^+]

1. Scale:

   • Ranges from 0 to 14.
   • pH < 7: Acidic (higher H+H^+ concentration).
   • pH = 7: Neutral.
   • pH > 7: Basic/alkaline (lower H+H^+ concentration).

2. Examples:

   • Acidic: Lemon juice (~2), Vinegar (~3).
   • Neutral: Pure water (7).
   • Basic: Baking soda (~9), Ammonia (~11).

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3. Importance:

   • Biological: Enzyme activity and metabolic processes depend on a specific pH (e.g., blood pH is ~7.4).
   • Environmental: pH affects soil fertility and aquatic ecosystems.
   • Industrial: Used in chemical manufacturing and food processing.

4. Buffers:

   • Maintain a stable pH in a system by neutralizing acids or bases.
   • Example: Bicarbonate buffer system in blood.

5. Calculation:

   • For strong acids/bases: pH=−log?[H+]pH = -\log[\text{H}^+].
   • For weak acids/bases: Use KaK_a or KbK_b to find H+H^+, then calculate pH.

Quick Facts:

• The pH scale is logarithmic: a change of 1 pH unit equals a tenfold change in H+H^+ concentration.
• Indicators: Substances like litmus paper or phenolphthalein are used to visually detect pH changes.