4.8-4.9 Acid-Base, Gas, and
Redox Reactions
Acid-Base Reactions
• Neutralization reactions: Acid reacts with Base to
neutralize each other producing water (or a weak
electrolyte) and an ionic compound (a salt).
• Arrhenius’s definition of acids and bases:
– Acid: substances that produce H+ ions in aqueous
solution. Protons combine with water molecules to form
H3O+(aq).
– Bases: substances that produce OH- ions in aqueous
solution
Types of Acids
• Polyprotic acids: Contains more than one ionizable
hydrogen.
– Example: H2SO4(aq) is considered diprotic (2 ionizable
protons). H3PO4(aq) is considered triprotic (3 ionizable
proton).
How many ionizable protons does HCl(aq) release?
1 (monoprotic)
How about acetic acid (HC2H3O2)?
1 (monoprotic)
Sample Problem
Write the molecular and a net ionic equation for the
reaction that occurs between aqueous H2SO4 and
aqueous LiOH.
H2SO4(aq) + 2LiOH(aq)  2H2O(l) + Li2SO4(aq)
2H+(aq) + 2OH-(aq)  2H2O(l) (# of moles reduce)
Acid-Base Titrations
• Titration: a solution of known concentration is
reacted with a solution of unknown concentration.
• Equivalence Point: the # of moles of OH- = # of
moles of H+. In a titration this is usually signaled by
an indicator.
• Titration formula: MAVA = MBVB
Sample Problem
The titration of 20.0 mL of an H2SO4 solution of unknown
concentration requires 22.87 mL of a 0.158 M KOH solution to
reach the equivalence point. What is the concentration of the
unknown H2SO4 solution?
H2SO4(aq) + 2KOH(aq)  K2SO4(aq) + 2H2O(l)
MAVA=MBVB
2MA(20.0 mL H2SO4) = (0.158 M KOH)(22.87 mL KOH)
(0.158 M)(22.87 mL)
MA = --------------------------------- = 9.03X10-2 M H2SO4(aq)
(2)(20.0 mL)
Gas Evolution Reaction
• Two aqueous solutions are mixed and a gas is
produced.
• Some intermediate products decompose further to
gain stability.
– Be familiar with the fact that:
• H2CO3 breaks down to H20(l) and CO2(g)
• H2SO4 breaks down to H2O(l) and SO2(g)
• NH4OH breaks down to H2O(l) and NH3(g)
Sample Problem
Write a molecular equation for the gas-evolution
reaction that occurs when you mix aqueous
hydrobromic acid and aqueous potassium sulfite.
HBr(aq) + K2SO3(aq)  KBr(aq) + H2SO3(aq)  KBr(aq) + H2O(l) + SO2(g)
2HBr(aq) + K2SO3(aq)  2KBr(aq) + H2O(l) + SO2(g)
Oxidation-Reduction Reactions (Redox)
• In a redox reaction, electrons are transferred (or shared unevenly)
between one reactant and the other.
• Oxidation: Loss of electrons or gain of oxygen
• Reduction: gain of electrons or loss of oxygen
• Oxidizing agent: the substance that is reduced
• Reducing agent: the substance that is oxidized
Great mnemonic device:
LEO the lion goes GER.
Loss Electrons Oxidation Gain Electrons Reduction
Use The Rules for Signing Oxidation #
Assign an oxidation state to each of atom in each element, ion, or compound.
a.) Cr
b.) Cr3+
c.) CCl4
d.) SrBr2
e.) SO3
f.) NO3a.) Cr = 0
b.) Cr3+ = +3
c.) C = +4 Cl = -1
d.) Sr = +2 Br = -1
e.) S = +6 O = -2
f.) N = +5 O = -2
Another Sample Problem
Use oxidation states to identify the element that is
oxidized and the element that is reduced in the
following redox reaction. Also indicate the oxidizing
agent and the reducing agent.
Sn(s) + 4HNO3(aq)  SnO2(s) + 4NO2(g) + 2H2O(l)
Sn is oxidized and N is reduced
N is the oxidizing agent and Sn in the reducing agent.
Chapter 4 pg. 189 #’s 80, 84, 88, 90, 92, & 96 (only the a’s)
Study for Exam