1.12.1 - 1.12.2 acid-base and pH definitions and equations

acid-base equilibria

transfer of protons between substances

Brønsted-Lowry acid

proton donor

Brønsted-Lowry base

proton acceptor

Arrhenius acid

dissociates in water to produce H⁺ ions

Arrhenius base

dissociates in water to produce OH^- ions

Lewis acid

electron pair acceptor

Lewis base

electron pair donor

concentrated vs dilute

• concentrated: large amount of dissolved solute per unit volume

• dilute: small amount of dissolved solute per unit volume

strong acid

completely dissociate into H⁺ ions in an aqueous solution

• dissociation reaction goes to completion

weak acid

dissociates only slightly into H⁺ions in aqueous solution

• dissociation reaction is reversible

strong base

completely dissociates in aqueous solution

• dissociation reaction goes to completion

weak base

dissociates only slightly in aqueous solution

• dissociation reaction is reversible

base vs alkali

• base - reacts with acid to produce salt and water in a neutralisation reaction

• alkali - a soluble base that releases OH^- ions

strong alkali

completely dissociates in aqueous solution to release OH^-

weak alkali

dissociates only slightly in aqueous solution to release OH^-

typical weak acids

typical strong bases

typical weak bases

• weak acids: carboxylic acids

• strong bases: metal hydroxides

• weak bases: NH₃, amines

dissociation of

• strong acid

• weak acid

• HCl → H⁺ + Cl^-

• CH₃COOH ⇌ H⁺ + CH₃COO^-

dissociation of

• strong base

• weak base

• KOH → K⁺ + OH^-

• NH₃ + H⁺ ⇌ + NH₄⁺

conjugate acid

the substance formed when the base accepts H⁺

• weakly acidic

conjugate base

the substance formed when the acid loses H⁺

• weakly basic

monoprotic acid

donates one H⁺ ion per molecule, e.g.

HCl → H⁺ + Cl^-

diprotic acid

donates two H⁺ ions per molecule, e.g.

H₂SO₄ → 2 H⁺ + SO₄^2-

triprotic acid

donates three H⁺ ion per molecule, e.g. H₃PO₄

H₃PO₄ → 3 H⁺ + PO₄^3-

amphiprotic

able to donate and accept H⁺

• e.g. water

  • donates H⁺ to form OH^- ion (hydroxide ion)

  • accepts H⁺ to form H₃O⁺ ion (hydronium ion)

pH

a logarithmic scale used to measure the concentration of hydrogen ions

why is pH used?

because the concentration of H⁺ in aqueous solution covers a very wide range

equations that link pH and H⁺ concentration

pH = -log₁₀[H⁺]

[H⁺] = 10^-pH

degree of accuracy for pH

reason

always give to 2 decimal places

a pH difference of 1 means a