Acids, Bases and pH Calculations

Ever wondered how scientists measure the strength of acids in your stomach or cleaning products? It's all about understanding how acids donate protons $H+$ whilst bases accept them.

Conjugate acid-base pairs are formed when acids lose a proton - they differ by exactly one hydrogen ion. For example, when HCl donates a proton, it becomes Cl⁻, making HCl/Cl⁻ a conjugate pair.

The pH scale uses the formula pH = -log₁₀$H+$ to convert tiny hydrogen ion concentrations into manageable numbers. Remember, lower pH means more acidic (more H+ ions), whilst higher pH means more basic.

For weak acids, we use the acid dissociation constant (Ka) to show how much the acid actually breaks apart at equilibrium. Converting this to pKa = -log₁₀(Ka) makes comparisons easier - larger pKa values indicate weaker acids.

Quick Tip: When calculating weak acid pH, you can often assume the $H+$ is negligible compared to the initial acid concentration, simplifying your maths considerably.

To find pH of strong bases, use the ionic product of water: Kw = $H+$[OH⁻] = 1 × 10⁻¹⁴ at 25°C. This constant relationship lets you calculate $H+$ from [OH⁻] and vice versa.