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Wize University Chemistry Textbook > Acids and Bases

Definitions of Acids and Bases

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Definitions of Acids and Bases


Arrhenius definition: compounds identified as producing H+ or OH- ions:
  • Acids produce
    H3O+
    aka
    hydronium ions
    :
HCl(g)+H2O(l)→H3O+(aq)+Cl−(aq)HCl(g)+H_2O(l)\to H_3O^+(aq) +Cl^{-}(aq)
  • Bases produce
    OH-
    aka
    hydroxide
    ions:
NaOH(s)→Na+(aq)+OH−(aq)NaOH(s)\to Na^{+}(aq)+OH^-(aq)

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**Bronsted - Lowry definition: compounds identified as H+ acceptors or donors
  • Acids
    donate
    H+ ions
HCl(g)+H2O(l)→H3O+(aq)+Cl−(aq)HCl(g)+H_2O(l)\to H_3O^+(aq)+Cl^-(aq)
  • Bases
    accept
    H+ ions
NH3(g)+H2O(l)⇌NH4+(aq)+OH−(aq)NH_3(g)+H_2O(l)\rightleftharpoons NH_4^+(aq)+OH^{-} (aq)
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Lewis definition: compounds identified as electron acceptors or electron donors
  • Acids: electron
    acceptors
    (anions/cations:
    cations
    ), and we call them (nucleophiles/electrophiles):
    electrophiles
  • Bases: electron
    donors
    and we call them nucleophiles/electrophiles:
    nucleophiles
    Examples: ligands, --:NH2

Wize Concept
Recall: Together, a Lewis acid and base can form a specific type of bond (when the Lewis base donates a pair of electrons to the Lewis acid to form a bond):
coordinate covalent
bond


Example: In the following reaction between NH3 and BH3, which is acting as the Lewis acid and which is acting as the Lewis base?


NH3 is donating its pair of electrons to BF3.
NH3 is acting as the Lewis Base (donating a pair of electrons)
BF3 is acting as the Lewis Acid (accepting a pair of electrons)


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Wize Tip
If we remember the definitions of acids and bases in alphabetical order, we can remember that the definitions go from simplest to most complex:

Arrhenius definition-acids and bases produce H+ or OH- ions

Bronsted-Lowry definition-acids and bases are H+ donors or acceptors

Lewis definition-acids and bases are electron pair acceptors or donators.


Wize Tip
Think of the acid HCl to remember the Bronsted-Lowry definition of an acid. Acids are proton (H+) donors.

Then, to remember the Lewis acid definition, remember that since acids donate a proton they do they opposite for electrons...they accept electrons!

Bases on the other hand are proton acceptors and since they accept protons, they do the opposite for electrons...they donate them!

Extra Practice
Acid Base Intro Activity
Does BH3 act as a lewis acid or lewis base?
In the reaction below which compound is the Lewis acid?
In the reaction below which compound is the Lewis acid?
In the reaction below which compound is the Lewis acid?
Which of the following are Lewis Acids?
Acids and Bases: Definitions
The definition of an amphoteric compound is:
In the reaction below which compound is the Lewis acid?
Acids and Bases
Choose the compounds below that are likely to function as Lewis Acids
Acids and Bases: Conjugate
In each equation, label the acids, bases and conjugate acid-base pairs
NH3+H3PO4↔NH4++H2PO4−NH_3+H_3PO_4 \leftrightarrow NH^+_4+H_2PO^-_4
CH3O−+NH3↔CH3OH+NH2−CH_3O^-+NH_3 \leftrightarrow CH_3OH+NH^-_2
How many pairs below represent a conjugate acid/base pair?
HCl / OCl−HCl\ /\ OCl^-
H2SO4/SO42−H_2SO_4/SO_4^{2-}
Acid Base Intro Activity
Does BH3 act as a lewis acid or lewis base?
Consider the following two questions regarding solubility and acid/base chemistry: