Acids, Bases and Buffers

This lesson covers Brønsted-Lowry acid-base theory, pH calculations for strong acids, strong bases, weak acids, and buffer solutions, the ionic product of water (Kw), polyprotic acids, titration curves for all four acid-base combinations, buffer calculations, and the Henderson-Hasselbalch equation. A thorough understanding of acid-base chemistry is essential for A-Level Chemistry and has applications in biology, medicine, and industry. This material aligns with the AQA and OCR A specifications for A-Level Chemistry.

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Brønsted-Lowry Theory

Key Definition: A Brønsted-Lowry acid is a proton (H⁺) donor. A Brønsted-Lowry base is a proton (H⁺) acceptor.

In every acid-base reaction, there is a transfer of a proton from the acid to the base. The species formed when an acid loses a proton is called its conjugate base. The species formed when a base gains a proton is called its conjugate acid. Every acid-base reaction involves two conjugate pairs.

For example: CH₃COOH + H₂O ⇌ CH₃COO⁻ + H₃O⁺

Species	Role	Conjugate partner
CH₃COOH	Acid (donates H⁺)	CH₃COO⁻ (conjugate base)
H₂O	Base (accepts H⁺)	H₃O⁺ (conjugate acid)