pH Scale & Ion Equilibrium
Determine aqueous solution pH from hydronium ion molarity and observe indicator color transitions.
Scientific Concept & Governing Equations
The potential of hydrogen (pH) is defined as the negative logarithm (base 10) of the activity of hydronium ions in an aqueous solution. In dilute solutions, concentration in molarity approximates activity:
Water autoionizes according to the equilibrium 2H₂O(l) ⇌ H₃O⁺(aq) + OH⁻(aq). At 25°C, Kw = [H₃O⁺][OH⁻] = 1.0 × 10⁻¹⁴, requiring that pH + pOH always equals 14.00.
Model Assumptions & Boundary Conditions
- Solution temperature is fixed at standard 25°C (298.15 K).
- Solute activity coefficients are assumed equal to 1.0 (ideal dilute solution).
- Autoionization constant Kw is assumed precisely 1.00 × 10⁻¹⁴.
Frequently Asked Questions
Why is the pH scale logarithmic?
Because aqueous hydrogen ion concentrations range over 14 orders of magnitude (from 1 M to 10⁻¹⁴ M), a base-10 logarithmic scale compresses this immense spectrum into an accessible 0 to 14 index.
What does pH 7 signify chemically?
At 25°C, pH 7 corresponds to equal concentrations of hydronium [H₃O⁺] and hydroxide [OH⁻] ions (each 1.0 × 10⁻⁷ mol L⁻¹), representing chemical neutrality.
More from Alok Das
These interactive tools are personal side-projects built for exploration and utility. My primary professional commitment is in M.Sc. Chemistry, analytical research, and laboratory methodology.