Reactions in Aqueous Solution I:
Acids, Bases, and Salts
Chapter 10
Properties of Acidic Solutions
• They have a sour taste
– Vinegar is 5% acetic acid (tastes sour)
• Change the colors of indicators
– Blue litmus turns red
• React with active metals to produce hydrogen
– Mg(s) + H2SO4(aq)  MgSO4(aq) + H2(g)
• React with metal oxides and hydroxides to form salts
and water
– HCl(aq) + LiOH(aq)  LiCl(aq) + H2O(l)
• Aqueous solutions conduct electric current
Properties of Basic Solutions
• They taste bitter and feel slippery
• Change color of indicators
– Red litmus turns blue
• React with acids to form salts and water
– HCl(aq) + LiOH(aq)  LiCl(aq) + H2O(l)
• Aqueous solutions conduct electricity
Arrhenius Theory for Acids and
Bases
• An acid is a substance that contains _____ and
produces ____ in aqueous solutions
• A base is a substance that contains _____ and
produces ____ in aqueous solutions
• Neutralization is defined as the combination of H+
ions with OH- ions to form H2O molecules
– This is a common acid/base reaction
– HBr(aq) + NaOH(aq) What is the net ionic equation?
The Hydronium Ion
• H+(aq) does not exist in aqueous solutions.
The ion exists as H+(H2O)n
– n is some small integer
– The hydrated ion is commonly represented as H3O+
• n=1
– Recall that we used H+(aq) as an abbreviated form
for H3O+(aq). They indicate the same hydrated ion
in aqueous solutions.
Brønsted-Lowry Theory
• An acid is defined as a proton _____ (H+), and
a base is defined as a proton _____.
– Any hydrogen-containing molecule or ion that can
release a proton is a acid, while any molecule or
ion that can accept a proton is a base.
– HBr(aq) + H2O(l)  Br-(aq) + H3O+(aq)
– NH3(aq) + H2O(l)  NH4+(aq) + OH-(aq)
Are these reversible reactions? Indicate the arrows.
Brønsted-Lowry Theory
• An acid-base reaction is simply the transfer of a
proton from an ____ to a _____
– Indicate the transfer on the previous reactions
• Notice that there is a newly created acid and base
on the product side of the equation
– HBr(aq) + H2O(l)
Br-(aq) + H3O+(aq)
acid1
base2
base1
acid2
– NH3(aq) + H2O(l)
NH4+(aq) + OH-(aq)
• Identify the newly-created acid and base on the product side
Brønsted-Lowry Theory
• Notice that an acid creates a _____ upon
losing a proton. Additionally, the base
creates an ____ upon gaining the proton
– Illustrate with previous reactions
• Designated with the same subscript
• These are called conjugate acid-base pairs
– The two species differ by only a _____
HF(aq) + H2O(l) ????
Brønsted-Lowry Theory
• The stronger the acid, the _______ is its conjugate
base. The weaker the acid, the ____ is its
conjugate base.
– This also holds for strong and weak bases
– This will indicate how to draw the arrows and the
predominant species present
• The direction of the reaction depends on the strength of the
acid (covered later)
– Water can act as an acid or a base depending on the
other species with which it reacts
The Autoionization of Water
• Pure water ionizes slightly to produce hydrated
hydrogen ions and hydroxide ions
– Illustrate
– H2O(l) + H2O(l)  H3O+(aq) + OH-(aq) or 2H2O(l) 
H3O+(aq) + OH-(aq)
• Concentration of OH- and H3O+ in water is 1.0  10-7 M
– Identify the conjugate acid-base pairs and the relative
lengths of the arrows
– Water undergoes an acid/base reaction and autoionizes
Amphoterism
• Amphiprotic – proton transfer reactions in
which a substance can act as either an acid
or a base
– Water is amphiprotic since it can behave as an
acid or base
• Amphoteric (optional) -
Strengths of Binary Acids
• Acid strength increases with ______ bond
strength. The proton is easier to remove
– Bond strength HF>>HCl>HBr>HI
– Acid strength HF<<HCl<HBr<HI
• HI is a very strong acid
– Group VIA hydrides, Bond strength
H2O >> H2S > H2Se > H2Te
• Place these acids in order of increasing bond
strength
Strengths of Binary Acids
• Acid leveling (leveling effect of water)
– It is very difficult to differentiate the strengths of HCl, HBr, and HI
in dilute aqueous solutions. This is because H3O+ is the strongest
acid that can exist in aqueous solution. All acids stronger than
H3O+(aq) react almost completely (i.e. ionize completely) with
water to produce H3O+(aq).
• All strong acids have nearly the same strength in water
• HI, HBr, HCl
• Acid strengths can be distinguished, however, in nonaqueous
solutions
• Likewise, any base stronger than OH- reacts almost
completely with H2O to produce OH-(aq)
– Not many bases are stronger than OH- (NH2-)
Ternary Acids
• Ternary acids are hydroxyl compounds of nonmetals
that produce H3O+ in water
– HNO3 and H3PO4 (write structures and illustrate the OH’s)
• The electronegative nonmetal and oxygen combination pulls electron
density away from the hydrogens
– Hydrogen atom leaves as H+ (combines with H2O)
• On the contrary, hydroxyl compounds of metals
commonly produce hydroxide ions in water and are
bases (Don’t confuse the acids from the bases)
Ternary Acids
• Many ternary acids possess more than one
proton to donate to a base (e.g. H2O). These
are termed as _______ acids.
– Each ionization step can be represented separately
– Each successive proton, H+, is more difficult to
remove. This is reflected in the extent of ionization
– H2SO4(aq) + H2O(l)
HSO4-(aq) + H3O+(aq)
– HSO4-(aq) + H2O(l)
SO42-(aq) + H3O+(aq)
• H2SO4 is a much stronger acid than HSO4-
Ternary Acids
• The strength of a ternary acid also increases with
decreasing O-H bond strength
• The strength of a ternary acid containing the same
central element increases with increasing oxidation
state of the central atom
– Increasing oxidation state scales with the number of _____
atoms
– H2SO4 and H2SO3
– HClO, HClO2, HClO3, and HClO4
What can you say about O-H bond strengths in these acids?
Ternary Acids
• For most ternary acids containing different
elements in the same oxidation state from
the same group in the periodic table, acid
strengths increase with increasing
electronegativity of the central atom
– Acid strength would decrease going down the
periodic table
– H2SeO4 and H2SO4
– HClO4, HBrO4, and HIO4
Acid Strengths
There is another table in your books (Table 10-2)
Acid Strengths
• An acid will react almost completely with
the conjugate base of any acid below it in
these tables
– The direction of the arrows can be determined
from this information
– HCN(aq) + H2O(l) ????
– H3O+(aq) + F-(aq) ????
– H2PO4-(aq) + SO42-(aq) ????
The stronger acid wins!!!
Reaction of Acids and Bases
• Strong acids and bases
– H2SO4(aq) + LiOH(aq)
• Write the formula unit, total ionic, and net ionic
equations
– Formation of water and salt in the formula unit
equation
• Salt – anion of the acid and cation of the base
– Net ionic equation from the reaction of strong
acids and bases that form soluble salts
• H+(aq) + OH-(aq)  H2O(l)
Reactions of Acids and Bases
• H2SO4(aq) + Ba(OH)2(aq)
Write the formula unit, total ionic, and net ionic
equation
This is the only reaction of this type (formation of an
insoluble salt)
Demo:
Extra practice
• Write the formula unit equation for an acid and
base that will form Ca(ClO3)2
• MgSO4 formation
Reactions of Acids and Bases
• Reactions of weak acids and weak bases
– These mostly produce soluble salts
– CH3COOH(aq) + NH3(aq)
– HClO2(aq) + NH3(aq)
Name the salts that are formed
Reactions of Acids and Bases
• Reactions of weak acids with strong bases
(soluble)
– These produce water and a soluble salt
– Nitrous acid + sodium hydroxide
• Write the formula unit, total ionic, and net ionic
equations
– Practice
• Acetic acid + calcium hydroxide
Reactions of Acids and Bases
• Reactions of strong acids with weak bases
– These form soluble salts
– Nitric acid + ammonia
• Write the three equations for this reaction
Acidic and Basic Salts
• When stoichiometric amounts of an acid and base are
mixed a ______ salt is formed
– H2SO4(aq) + 2NaOH(aq)  Na2SO4(aq) + 2H2O(l)
• Na2SO4 is a _____ salt
• No protons remaining for reacting further with a base
• When less than stoichiometric amounts of a base reacts
with a polyprotic acid an _____ salt is formed
– H2SO4(aq) + NaOH(aq)  NaHSO4(aq) + H2O(l)
• Name the acid salt
Acidic and Basic Salts
• H2SO4(aq) + NaOH(aq)  NaHSO4(aq) + H2O(l)
– The acid salt, NaHSO4, is still capable of
neutralizing bases since it has a proton to donate
– The acidic salt is weak, but it still can react with
strong bases
– NaHSO4-(aq) + NaOH(aq)  Na2SO4(aq) + H2O(l)
Acidic and Basic Salts
• When less than stoichiometric amounts of an
acid are mixed with a polyhydroxy base an
_____ salt is formed
– Ba(OH)2(aq) + HCl(aq)  Ba(OH)Cl(aq) + H2O(l)
• Ba(OH)Cl is a basic salt since it can react (and
neutralize) a strong acid
– Ba(OH)Cl(aq) + HCl(aq)  BaCl2(aq) + H2O(l)
• What is BaCl2(aq)?
– Another: Al(OH)3
Lewis Theory
• An acid is any species that ______ a pair of
electrons. A base is any species that _____
a pair of electrons
• _______ is defined a coordinate covalent
bond formation
– The electron pair does not move. It originally
resides on one of the atoms on the base. The
electron pair will be shared between the acid
and base
Lewis Theory
• NH3(aq) + H2O(l)  NH4+(aq) + OH-(aq)
– Show detail of electron pair on NH3 bonding
with H+ from water
• Almost any species with an ____ ____ of
electrons can act as a base
– These reactions are common for acids
containing only six electrons in the highest
energy shell (open sextet)
• AlCl3(s) + Cl-(aq)  AlCl4-(aq)
• AlCl3(s) possessed on open sextet
Lewis Theory
• NaF(aq) + BF3(g) 
– Could this be an Arrhenius or Bronsted-Lowry
acid/base reaction?
– How about the previous reactions? How would they be
classified?
• Many organic and biological reactions are acid/base reactions
that can only be explained by the Lewis theory.
Problem-solving tip on page 390
Classify the reaction
NH3(aq) + HBr  NH4+(aq) + Br-(aq)
Preparation of Acids
• Binary Acids
– React elements with hydrogen (Cl2 + hydrogen)
• Volatile Acids
– React appropriate salt with a nonvolatile acid
– NaCl(s) + H2SO4(l)  HCl(g) + NaHSO4(s)
• Also used for HF
– NaI(s) + H3PO4(l)  HI(g) + NaH2PO4(s)
• Also used for HBr
• Name the salts that are formed
H2SO4 cannot be used to form HBr and HI
Preparation of Acids
• Ternary acids
– Nonmetal oxides (acid anhydrides) and water
• No change in oxidation numbers
– N2O5(l) + H2O(l)  2HNO3(aq)
– 2CrO3(s) + H2O(l)  H2Cr2O7(aq)
DEMO:
Preparation of Acids
• Reaction of halides and oxyhalides of some
nonmetals react with water to produce a
binary and ternary acid
– PCl5(s) + 4H2O(l)  H3PO4(aq) + 5HCl(aq)
– POCl3(s) + H2O(l) 
DEMO: