Glossary


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A

acid

a chemical that:
  • dissociates in water, releasing H+ ions (protons) (Arrhenius and Brønsted-Lowry definitions)

  • accepts electrons in a chemical reaction (Lewis definition)

  • tastes sour

acid dissociation constant

(Ka) is the equilibrium constant for the dissociaton of acid HA into H+ and A-. The larger the number, the stronger the acid and the more it dissociates in water.

    Ka = [H+][A-]
             [HA]

amphoteric

a substance that has both a conjugate acid and a conjugate base ("goes both ways").  For example, the HSO4- ion is amphoteric, because it has both a conjugate acid (H2SO4) and a conjugate base (the SO42- ion).

B

base

a chemical that:
  • dissociates in water, releasing OH- ions (Arrhenius definition)

  • accepts H+ ions in a chemical reaction (Brønsted-Lowry definition)

  • donates electrons in a chemical reaction (Lewis definition)

  • tastes bitter

base dissociation constant

(Kb) is the equilibrium constant for the ability of base B to pull an H+ away from water to form HB+ and OH-.  The larger the number, the stronger the base.

    Kb = [HB+][OH-]
               [B]

buffer

a weak acid or weak base that prevents the pH of a solution from changing drastically until all of the buffer ions have been completely neutralized.

A buffer is most effective at pH values near its pKa.

Weak acids & bases act as buffers in aqueous solutions.  (For strong acids & Bases, water acts as the buffer.)

C

conjugate acid

an acid formed by adding H+ to a base.  For example, the conjugate acid of NH3 is the NH4+ ion; the conjugate acid of the HSO4- ion is H2SO4.

conjugate base

a base formed by removing H+ from an acid. For example, the conjugate base of HCl is the Cl- ion; the conjugate base of the NH4+ ion is NH3.

D

dissociation

the process of an ionic compound or an acid splitting into ions. For example:

    HCl --> H+ + Cl-

    NaOH --> Na+ + OH-

H

hydronium ion

H3O+, which is the conjugate acid of H2O.

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