Detailed Breakdown: Acids / Bases
The Proton-Transfer Model: Brønsted-Lowry theory defines acids as proton donors and bases as proton acceptors. This emphasizes 'conjugate acid-base pairs,' where every acid creates a potential base upon losing its proton. It is a more robust model than simple Arrhenius theory.
Strong vs. Weak: Degree of Ionization: A strong acid like $\ce{HCl}$ ionized 100% in water, creating a high $[\ce{H+}]$ and low pH. A weak acid like ethanoic acid only partially ionizes, establishing an equilibrium. The strength is measured by $K_a$ or $pKa$: the lower the $pKa$, the stronger the acid.
Buffer Logic and Resistance to Change: A buffer is a mixture of a weak acid and its conjugate base. It can neutralize added $\ce{H+}$ (via the base) or $\ce{OH-}$ (via the acid) to keep the pH stable. This is how human blood maintains a precise pH around 7.4.