ACIDS , BASES and
BUFFERS
ACID
A good example of an Arrhenius acid is
hydrochloric acid, HCl. It dissolves in water to
form the hydrogen ion and chlorine ion:
+
−
HCl → H (aq) + Cl (aq)
Arrhenius Definition:
An Arrhenius base is a substance that
−
dissociates in water to form hydroxide (OH )
ions. In other words, a base increases the
concentration of OH − ions in an aqueous
solution.
BASE
A good example of an Arrhenius base is
sodium hydroxide, NaOH. It dissolves in
water to form the sodium ion and hydroxide
ion:
NaOH → Na+ (aq) + OH − (aq)
BRONSTED LOWRY DEFINITION
A Brønsted-Lowry acid is any species that is capable of
donating a proton H+
A Brønsted-Lowry base is any species that is capable of
accepting a proton, which requires a lone pair of electrons
to bond to the H +
Water is amphoteric, which means it can act as both a
Brønsted-Lowry acid and a Brønsted-Lowry base.
BRONSTED LOWRY DEFINITION
The conjugate base of a Brønsted-Lowry acid is the
species formed after an acid donates a proton.
The conjugate acid of a Brønsted-Lowry base is the
species formed after a base accepts a proton.
BRONSTED LOWRY DEFINITION
BRONSTED LOWRY DEFINITION
LEWIS ACID
accept an electron pair. Lewis Acids are Electrophilic
meaning that they are electron attracting.
• Various species can act as Lewis acids. All cations are
Lewis acids since they are able to accept electrons.
(e.g., 𝐂𝐮𝟐+ , Fe𝟐+ )
• An atom, ion, or molecule with an incomplete octet of
electrons can act as an Lewis acid (e.g., 𝐁𝐅𝟑 , 𝐀𝐥𝐅𝟑 ).
LEWIS BASE
donate an electron pair. Lewis Bases are Nucleophilic
meaning that they “attack” a positive charge with their
lone pair.
Each of the following can "give up" their electrons to an
acid, e.g., 𝐎𝐇 − , 𝐂𝐍 − , 𝐍𝐇𝟑
Strong acids react essentially completely with
+
water to give H and the corresponding anion.
Strong bases dissociate essentially completely
in water to give OH − and the corresponding
cation.
Strong acids and strong bases are both strong
electrolytes.
Weak acid is partially dissociated in an
aqueous solution.
Weak base is partially dissociated in an
aqueous solution