pH – Full Information

Definition:
pH is a scale used to specify the acidity or basicity (alkalinity) of an aqueous solution. It stands for "potential of hydrogen" or "power of hydrogen."

pH Scale:

• Ranges from 0 to 14.

  • pH < 7 → Acidic

  • pH = 7 → Neutral (pure water)

  • pH > 7 → Basic (alkaline)

Mathematical Definition:

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

• [H+][\text{H}^+] is the concentration of hydrogen ions in moles per liter.

• Example: If [H+]=1×10−7[\text{H}^+] = 1 \times 10^{-7}, then pH = 7.

Measurement of pH:

1. Indicators:

   • Substances like litmus, phenolphthalein, or methyl orange change color with pH.

   • Useful for qualitative determination.

2. pH Meters:

   • Electronic device with a glass electrode.

   • Provides accurate quantitative measurement.

3. pH Test Strips:

   • Paper strips with color indicators.

   • Used for quick testing.

Biological and Environmental Importance:

• Human Blood: Maintains pH ~7.35–7.45 (slight alkalinity). pH imbalances can be life-threatening.

• Soil pH: Affects plant growth and nutrient availability.

• Aquatic Life: Water pH affects the health of fish and aquatic ecosystems.

• Digestion: Stomach acid has a very low pH (~1.5–3.5) to aid digestion.

Applications of pH:

• Agriculture: Soil treatment, fertilizer usage.

• Medicine: Drug formulation, body fluid testing.

• Chemistry and Industry: Acid-base titrations, manufacturing processes.

• Food & Beverage: pH control for preservation and flavor.

Common Acids and Bases:

Buffer Solutions:

• Solutions that resist changes in pH when small amounts of acid or base are added.

• Essential in biological systems, like maintaining blood pH.