Acids, Bases & pH

01 What Are Acids and Bases?

Brønsted-Lowry definition: acids are proton (H⁺) donors; bases are proton acceptors. When an acid dissolves in water it increases H⁺ concentration. Bases decrease it. Strong acids (HCl, H₂SO₄) dissociate completely; weak acids (CH₃COOH - vinegar) only partially.

02 The pH Scale

pH = -log[H⁺]. Pure water has pH 7 (neutral). Below 7 = acidic, above 7 = basic (alkaline). Each unit is 10× change in concentration - pH 3 is 10,000× more acidic than pH 7. Your stomach acid is ~pH 1.5–2. Blood must stay at pH 7.35–7.45; a change of 0.4 is fatal.

03 Buffers

A buffer solution resists changes in pH when small amounts of acid or base are added. Your blood is buffered by carbonic acid / bicarbonate equilibrium (H₂CO₃ ⇌ H⁺ + HCO₃⁻). This is why you don't die from eating a lemon. Industrial buffers are essential in pharmaceuticals and food.

04 Key Facts

→Battery acid is ~pH 0.5. Bleach is ~pH 12.5. A difference of 12 pH units is 1 trillion-fold in H⁺ concentration.

→Soap is mildly alkaline (~pH 9–10) which is why it lifts oils and kills bacteria.

→Rainwater is naturally slightly acidic (pH 5.6) due to dissolved CO₂ forming carbonic acid.

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