A strong base is a substance that dissociates completely in water, producing hydroxide ions (OH⁻) and cations, so its OH⁻ concentration equals what you'd predict from stoichiometry alone. Common examples on the AP Chem exam are NaOH, KOH, and Ba(OH)₂.
A strong base dissociates 100% in water. Drop NaOH into water and you don't find any intact NaOH formula units floating around, just Na⁺ ions and OH⁻ ions. That "complete dissociation" detail is the whole point, because it means [OH⁻] comes straight from the concentration of the base (with a stoichiometry check for hydroxides like Ba(OH)₂, which releases two OH⁻ per formula unit).
The strong bases you'll actually see on the AP exam are the Group 1 hydroxides (NaOH, KOH, LiOH) and the heavier Group 2 hydroxides (Ba(OH)₂, Sr(OH)₂). Contrast this with a weak base like NH₃, which only partially reacts with water and leaves mostly intact molecules in solution. Strong vs. weak is about percent ionization, not how corrosive or concentrated something is. A dilute solution of NaOH is still a strong base.
Strong bases live at the heart of Unit 8. Learning objective AP Chem 8.4.A asks you to explain concentrations of major species when acids and bases mix, and the strong base is what drives those reactions to completion. Per 8.4.A.1, strong acid + strong base reacts quantitatively as H⁺(aq) + OH⁻(aq) → H₂O(l), and the pH of the final solution comes from whatever reagent is in excess. Per 8.4.A.2, when you mix a weak acid with a strong base, the OH⁻ converts weak acid into its conjugate base. If the weak acid is in excess, congratulations, you just built a buffer. That makes strong bases the standard tool for buffer-creation problems and for testing buffer behavior under 8.8.A. They also show up in Unit 3 (Topic 3.8), where particulate diagrams must show a strong base fully dissociated into separate ions, with zero intact formula units drawn.
Keep studying AP Chemistry Unit 8
Strong Acid (Unit 8)
Strong acid and strong base are mirror images. Both dissociate completely, and when mixed they neutralize via H⁺ + OH⁻ → H₂O. Exam problems hinge on figuring out which one is left over and using that excess to find pH.
Conjugate Base & Buffers (Unit 8)
Adding a strong base to excess weak acid converts some HA into A⁻, creating a buffer. This is the most common way the exam asks you to build a buffer from scratch, and Henderson-Hasselbalch handles the pH from there.
Equivalence Point (Unit 8)
In a weak acid titrated with a strong base, the equivalence point is basic (pH > 7) because all the acid has become conjugate base, which then reacts with water. Knowing the titrant is a strong base is what makes that prediction possible.
Representations of Solutions (Unit 3)
Topic 3.8 particulate diagrams are a sneaky way to test this term. A correct drawing of an NaOH solution shows only separated Na⁺ and OH⁻ ions surrounded by water. Any intact NaOH unit in the picture is wrong.
Strong bases show up constantly in Unit 8 calculations. A classic MCQ gives you volumes and molarities of a strong acid and strong base (like 25.0 mL of 0.200 M HCl with 15.0 mL of 0.300 M NaOH) and asks for the pH, which means finding moles of each, subtracting, and computing pH from the excess. Net ionic equations are another favorite, like mixing HClO₄ with Ba(OH)₂, where the answer reduces to H⁺ + OH⁻ → H₂O. Weak acid + strong base questions ask you to identify the predominant reaction (HA + OH⁻ → A⁻ + H₂O) and recognize when a buffer forms. Buffer questions test how adding a strong base shifts the conjugate base-to-acid ratio. On the free-response side, the 2022 exam (LR Q1) had a student react methyl salicylate with a stoichiometric amount of a strong base, so be ready to use strong bases in stoichiometry and synthesis contexts too, not just pH math.
A strong base dissociates completely (100% of NaOH becomes Na⁺ and OH⁻), so [OH⁻] equals the base concentration times its stoichiometric coefficient. A weak base like NH₃ only partially reacts with water, so you need its Kb and an equilibrium (ICE) setup to find [OH⁻]. The fastest way to lose points is treating NH₃ like NaOH and skipping the equilibrium.
A strong base dissociates 100% in water, so [OH⁻] comes directly from the base's concentration and stoichiometry, with no equilibrium calculation needed.
Memorize the short list: Group 1 hydroxides (LiOH, NaOH, KOH) and heavier Group 2 hydroxides like Ba(OH)₂, which gives two OH⁻ per formula unit.
Strong acid + strong base reacts completely as H⁺ + OH⁻ → H₂O, and the pH of the mixture comes from the moles of excess reagent divided by total volume.
Adding a strong base to an excess of weak acid converts HA into A⁻ and forms a buffer, whose pH you find with the Henderson-Hasselbalch equation.
In a particulate diagram, a strong base solution must be drawn as fully separated ions; drawing any intact formula units is a wrong answer.
Strong vs. weak describes percent ionization, not concentration. A dilute NaOH solution is still a strong base.
A strong base is a substance that dissociates completely in water to give OH⁻ ions, like NaOH, KOH, or Ba(OH)₂. Because dissociation is 100%, [OH⁻] equals the base's concentration (times 2 for hydroxides like Ba(OH)₂).
No. Strong refers to complete dissociation, while concentrated refers to how many moles are dissolved per liter. You can have a dilute strong base (0.001 M NaOH) or a concentrated weak base (5 M NH₃).
For a strong base, you find [OH⁻] directly from stoichiometry with no equilibrium math. For a weak base like NH₃, only a small fraction reacts with water, so you need Kb and an ICE table to find [OH⁻] and pH.
They react quantitatively: HA + OH⁻ → A⁻ + H₂O. If the weak acid is in excess, the leftover HA plus the A⁻ you made form a buffer, and you can find pH with Henderson-Hasselbalch. If the strong base is in excess, the leftover OH⁻ controls the pH.
Yes. Ba(OH)₂ dissociates completely, releasing two moles of OH⁻ per mole of base, so [OH⁻] is double the concentration of Ba(OH)₂. That factor of 2 is a classic trap in pH and net ionic equation problems.
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