A molecule that changes color depending on the pH of the solution it is in. It's sort of like a chameleon, but not. Actually, it's nothing like a chameleon.
Acid-Dissociation Constant (Ka)
The equilibrium constant for a reaction in which a reactant (an acid) donates a proton to water forming H3O+.
Acidic
A solution that has a greater concentration of H3O+ molecules compared to the concentration of OH- molecules.
Arrhenius Acid
A molecule that releases a proton (H+) in water.
Arrhenius Base
A molecule that releases hydroxide (OH-) in water.
Base-Dissociation Constant (Kb)
The equilibrium constant for a reaction in which a reactant (a base) accepts a proton from water forming OH-.
Basic
A solution that has a greater concentration of OH- molecules compared to the concentration of H3O+ molecules.
Brønsted-Lowry Acid
A molecule that donates a proton (H+) to a proton acceptor molecule.
Brønsted-Lowry Base
A molecule that accepts a proton (H+) from a proton donor molecule.
Buffer Capacity
The ability of a buffer solution to absorb added H+ or OH- without significant changes in pH.
Buffer Solution
A solution of a weak acid or base in equilibrium with its conjugate base or acid that resists large changes in pH.
Conjugate Acid
The molecule resulting after an acid donates a proton (H+).
Conjugate Acid-Base Pairs
An acid and its conjugate base or a base and its conjugate acid.
Conjugate Base
The molecule resulting after a base accepts a proton (H+).
Diprotic Acid
An acid that has two protons (H+) available to transfer to a base (or water).
Equivalence Point
The region of a titration curve that exhibits a sharp change in pH at which point equivalent amounts of acid and base have been mixed.
Hydronium Ion
The H3O+ ion that results when a proton is transferred to H2O.
Hydroxide Ion
The OH- ion that results when a proton is lost from H2O+.
Ion-Product Constant For Water
The equilibrium constant for the dissociation of water to give a hydronium ion and a hydroxide ion.
Lewis Acid
An electron-pair acceptor.
Lewis Base
An electron-pair donor.
Monoprotic
An acid that has just one proton to transfer.
Neutral
A solution that has an equal concentration of H3O+ and OH- molecules (1 × 10-7 M at 25° C).
Neutralization Reaction
A reaction between an acid and base that results in the production of H2O and brings the pH of the reaction solution closer to neutrality.
Percent Dissociation
The concentration of acid (or base) that dissociates at equilibrium divided by the initial concentration of acid.
PH Scale
The scale on which the acidity or basicity of a solution is measured. The pH equals –log([H3O+]).
PH Titration Curve
A plot of the pH of a solution (usually measured with a pH meter), versus the volume of added titrant.
Polyprotic Acid
An acid that can transfer two or more protons.
Principle Reaction
The proton transfer reaction of a weak acid/base equilibrium that progresses furthest to the right and has the largest equilibrium constant.
Strong Acid
An acid that nearly fully dissociates in water.
Subsidiary Reaction(s)
The reaction(s) involved in a weak acid/base equilibrium that do not contribute to significant changes in product concentrations (that is, reactions that are not the principle reaction).
Titration
The incremental addition of a strong acid or base to a solution of acid or base.