Advanced & Biological Effects
pH & pOH Calculation Example:
- Given [H⁺] = 1 × 10-5 mol/L, pH = -log₁₀(1e-5) = 5
- pOH = 14 - pH = 9
- [OH⁻] = 10-9 mol/L
Buffer Solutions: Buffers resist pH changes. Example: Acetic acid + sodium acetate buffer keeps pH stable near 4.7. Used in blood, labs, industry.
pH Color Indicators (Visual)
| pH | Indicator Color | Indicator |
|---|
| 1 | Red | Methyl Red |
| 4 | Orange | Methyl Orange |
| 7 | Green | Bromothymol Blue |
| 10 | Blue | Phenolphthalein |
| 13 | Purple | Universal Indicator |
Measurement Devices: pH meter (electrode), indicator paper, colorimetric sensors.
Calibration: Use standard buffer solutions (pH 4, 7, 10) for accurate results.
Biological Impact: pH affects enzyme activity, cell function, aquatic life, and nutrient availability. Extreme pH can be harmful to organisms.
Water Quality: pH outside 6.5-8.5 can cause corrosion, scaling, and toxicity in water systems.
Soil Science: pH affects nutrient solubility and plant growth.
Frequently Asked Questions:
- Why does pH + pOH = 14? This is true for pure water at 25°C due to the ion product of water (Kw = 1e-14).
- What is a buffer? A solution that resists changes in pH when acid or base is added.
- How does temperature affect pH? Higher temperature lowers pH of pure water (Kw increases).
- Why is blood pH tightly regulated? Enzyme function and oxygen transport depend on stable pH (7.35-7.45).
Formula Recap: [H⁺] = 10⁻ᵖᴴ, [OH⁻] = 10⁻ᵖᴼᴴ, pH + pOH = 14