📋 Summary — What This Chapter Covers

• Brønsted–Lowry theory: acids donate protons, bases accept them — and every reaction has a "conjugate" pair linked by that one proton.
• pH is just a compressed way of writing [H⁺] using logs: pH = −log[H⁺].
• Strong acids/bases dissociate almost 100% — an easy calculation. Weak acids/bases only partially dissociate — you need Kₐ.
• Kₐ and pKₐ measure how far a weak acid's equilibrium sits — bigger Kₐ (smaller pKₐ) = stronger acid.
• Kw (ionic product of water) links [H⁺] and [OH⁻] in any aqueous solution: Kw = [H⁺][OH⁻] = 1×10⁻¹⁴ at 298 K.
• Titration curves have a distinct S-shape, and their exact shape (start pH, jump size, equivalence pH) tells you whether you're dealing with strong/weak acid vs strong/weak base.
• Indicators are weak acids themselves — you must pick one whose colour-change range matches the vertical jump of the titration curve.
• Buffers = weak acid + its conjugate base (or weak base + conjugate acid) sitting together, resisting pH change by "soaking up" added H⁺ or OH⁻.
• The Henderson–Hasselbalch equation lets you calculate buffer pH directly, and also lets you design a buffer for a target pH.

1. Brønsted–Lowry Acids & Bases

Forget the old "acids taste sour" definitions. The Brønsted–Lowry theory defines everything in terms of one simple action: passing a proton (H⁺) from one species to another.

• A Brønsted acid = a proton donor. It gives away H⁺.
• A Brønsted base = a proton acceptor. It grabs H⁺.

Think of it like a game of catch with a single ball (the proton). Whoever throws the ball is the acid; whoever catches it is the base. That's genuinely the whole concept.

Conjugate Acid–Base Pairs

Here's the part students often find confusing at first: in a real reaction, the acid and base swap roles as the reaction proceeds, because it's an equilibrium — both directions are happening. A conjugate pair is simply two species (one reactant, one product) that differ by exactly one proton.

Look closely: CH₃COOH and CH₃COO⁻ are a conjugate pair (CH₃COOH loses one H⁺ to become CH₃COO⁻). Likewise H₂O and H₃O⁺ are a pair (H₂O gains one H⁺ to become H₃O⁺).