Strong Acids and Strong Bases
The seven strong acids and eight strong bases that ionize completely in water. Essential for pH calculations and acid-base reaction predictions.
Deciding if an acid or base ionizes completely, so [H+] or [OH-] comes straight from concentration with no ICE table.
Dilute aqueous solution; account for dissociation stoichiometry (e.g. Ca(OH)2 and other Group 2 hydroxides give 2 OH- per formula unit).
For ordinary aqueous general-chemistry calculations, treat anything not on this list as weak and use its Ka or Kb with an ICE table.
The Strong Acids and Strong Bases
The seven strong acids and the Group 1 and Group 2 strong bases that ionize essentially completely in water.
| Hydrochloric acid | HCl | Strong acid | HCl → H+ + Cl- | Most common lab acid; found in stomach acid |
| Hydrobromic acid | HBr | Strong acid | HBr → H+ + Br- | Used in organic synthesis |
| Hydroiodic acid | HI | Strong acid | HI → H+ + I- | Strongest of the hydrohalic acids |
| Nitric acid | HNO3 | Strong acid | HNO3 → H+ + NO3- | Oxidizing acid; reacts with metals below H in activity series |
| Sulfuric acid | H2SO4 | Strong acid | H2SO4 → H+ + HSO4- | Diprotic; first dissociation is strong, second is weak (Ka2 = 0.012) |
| Perchloric acid | HClO4 | Strong acid | HClO4 → H+ + ClO4- | Strongest common acid in aqueous solution |
| Chloric acid | HClO3 | Strong acid | HClO3 → H+ + ClO3- | Strong oxidizer; less common in labs |
| Lithium hydroxide | LiOH | Strong base | LiOH → Li+ + OH- | Used in CO2 scrubbers (spacecraft, submarines) |
| Sodium hydroxide | NaOH | Strong base | NaOH → Na+ + OH- | Lye; most common strong base in labs and industry |
| Potassium hydroxide | KOH | Strong base | KOH → K+ + OH- | Caustic potash; used in soap-making and batteries |
| Rubidium hydroxide | RbOH | Strong base | RbOH → Rb+ + OH- | Rare; follows Group 1 pattern |
| Cesium hydroxide | CsOH | Strong base | CsOH → Cs+ + OH- | Strongest Group 1 base; extremely hygroscopic |
| Calcium hydroxide | Ca(OH)2 | Strong base | Ca(OH)2 → Ca2+ + 2OH- | Slaked lime; limited solubility but fully dissociates what dissolves |
| Strontium hydroxide | Sr(OH)2 | Strong base | Sr(OH)2 → Sr2+ + 2OH- | Moderately soluble; used in sugar refining |
| Barium hydroxide | Ba(OH)2 | Strong base | Ba(OH)2 → Ba2+ + 2OH- | Used in titrations; forms clear solutions |
Important Notes
- "Strong" means the acid or base ionizes (dissociates) completely in dilute aqueous solution.
- Acids and bases outside this conventional general-chemistry list are treated as weak: they only partially ionize in water.
- Strong acids have very large Ka values, so ionization is effectively complete and the equilibrium lies far to the right.
- In water, strong acids are all leveled to H3O+ and strong bases to OH-: the solvent sets the strongest acid and base that can exist in aqueous solution, so the strong acids appear equally strong there.
- H2SO4 is diprotic: the first proton dissociates completely (strong), but the second has Ka2 = 0.012 (weak).
- Group 1 metal hydroxides are all strong bases and highly soluble. Group 2 hydroxides (Ca, Sr, Ba) are strong but have limited solubility.
- Mg(OH)2 is conventionally left off the strong-base list because it is so sparingly soluble (Ksp ≈ 8.9 × 10-12). The small amount that does dissolve dissociates essentially completely, like the other Group 2 hydroxides, but the low solubility keeps the attainable hydroxide concentration small.
Verification references: Conventional general-chemistry strong-acid and strong-base set; leveling effect per the IUPAC Gold Book.