•Acids were first recognized as a
distinct class of compounds because
of the common properties of their
aqueous solutions.
•Aqueous solutions have a sour taste (many are corrosive
and poisons).
•Acids change the color of acid-base indicators.
•Some acids react with active metals to release hydrogen
gas, H2.
Acids react with bases to
produce salts and water.
Some acids conduct an electric current.
•Used in petroleum refining, automobile
batteries, and used as a water-removing
agent (can cause serious burns).
•Used in making explosives (stains
skin and causes serious burns).
•Used for manufacturing fertilizers and
animal feed and for flavoring beverages.
•Used in food processing.
•Used in the manufacture of
plastics and as a fungicide.
•Aqueous solutions of bases have a bitter taste.
•Bases change the color of acid-base indicators.
•Dilute aqueous solutions of bases feel slippery.
•Bases react with acids to produce salts and water.
•Bases conduct electric current.
An Arrhenius acid is a chemical
compound that increases the concentration
of hydrogen ions, H+, in aqueous solution.
Examples: HCl, H2SO4, HI, HF
An Arrhenius base is a substance that increases the
concentration of hydroxide, OH-, in aqueous solution.
Examples: NaOH, LiOH, Ca(OH)2
A Brønsted-Lowry acid is a molecule or ion that is a
proton donor (H+).
A Brønsted-Lowry base is a molecule or ion, that is a
proton acceptor.
In a Brønsted-Lowry acid-base reaction, protons are
transferred from one reactant (the acid) to another (the
base).
HCO3 + HOH → H2CO3 + OHBase
Acid
A Lewis acid is an atom, ion, or molecule that accepts an
electron pair to form a covalent bond.
A Lewis base is an atom, ion, or molecule that donates
an electron pair to form a covalent bond.
A Lewis acid-base reaction is the formation of one or
more covalent bonds between an electron-pair donor and
an electron-pair acceptor.
•Pure water is a weak electrolyte and undergoes
self-ionization as seen below.
•Remember ionization is the process of adding or
removing electrons from an atom or molecule, which
gives the atom or molecule a net charge.
•In the self-ionization of water, two water molecules
produce a hydronium ion and a hydroxide ion by
transfer of a proton.

H 2O  H 2O  H3O  OH
hydronium ion
(Acid)
-
hydroxide ion
(Base)
Concentrations of hydronium ion (H3O+) and
hydroxide ion (OH-) are 1.0 x 10-7 mol/L in
water at 25 oC.
The product of [H3O+][OH-] = 1.0 x 10-14 and
the product is called the ionization constant
of water, Kw.
Note: [ ] means molar concentration (mol/L).
•Any solution in which [H3O+] = [OH-] is neutral.
•Any solution in which [H3O+] is greater than [OH-] is
acidic. Remember acids increase the concentration of
H3O+ in aqueous solutions.
•Any solution in which [OH-] is greater than [H3O+] is
basic. Remember bases increase the concentration of OHin aqueous solutions.
Instead of expressing acidity or basicity in
terms of the concentration of H3O+ or OH-, a
quantity called pH is used.
The pH scale
commonly has
values from 0 to 14
with a
pH value of 7
considered neutral.
pH values less than
7 are acidic and pH
value greater
than 7 are basic.
pH indicates the hydronium ion (H3O+) concentration
of a solution.
The pH of a solution is defined as the negative of the
common logarithm of the hydronium ion concentration.
pH = -log[H3O+] or pH = -log[H+]
pOH (hydroxide ion concentration)
pOH = -log[OH-]
pH + pOH = 14.0