Chem-To-Go
Lesson 38
Unit 10
PROPERTIES
Both acids and bases ionize or dissociate in
water
Acids: taste sour, conduct electricity, cause
certain indicators to change color, turn blue
litmus paper red, and react with metals to
form H 2 gas
Bases: taste bitter, feel slippery, conduct
electricity, and cause certain indicators to
change color, turn red litmus paper blue
PROPERTY: DISSOCIATION IN WATER
Acids and bases dissociate in water.
Dissociation reactions show this
phenomenon in a chemical equation.
EX. HCl
H + + Cl EX. Ca(OH) 2
2OH - + Ca 2+
 Notice the arrow. Acid/base dissociations are
reversible reactions.
 Some reactions are MORE reversible than others.
STRONG AND WEAK
Strong and weak do not mean the same
as concentrated and dilute.
HCl
H + + Cl-
Strong = completely dissociate when
dissolving in water; the forward dissociation
reaction is favored
Weak = partially dissociate when dissolving in
water; the dissociation reaction reaches
equilibrium (the forward and reverse reactions
are equally likely to occur)
STRONG ACIDS VS. WEAK ACIDS
NOTE: SAME IDEAS APPLY TO STRONG VS. WEAK BASES.
Strong Acids
 Only a few acids
dissociate completely
and remain dissociated.
 Halides: HCl, HBr, HI
 Ex. HCl + H 2 O  H + + Cl -
 Oxyacids: H 2 SO 4 , HClO 4 ,
HNO 3
 Ex. HNO 3 + H 2 O  H + + NO 3 -
 We’ll use strong acids
later during our unit in
calculations .
Weak Acids
 Most acids dissociate
during the forward
reaction, but the
reverse reaction
rebuilds the original
acid quickly.
 HC 2 H 3 O 2
H + + C 2H 3O 2 The reaction reaches
equilibrium, meaning the
ions often rebuild the acid.
FIRST ACID DEFINITION
 Arrhenius definition for acid: compound that
produces hydrogen ions (H + ) when dissolved in
water.
 Let’s write the dissociation reaction for the HCl example.
HCl + H 2O  H+ + ClOr
HCl + H 2O  H3O+ + ClH 3O + = Hydronium ion
FIRST BASE DEFINITION
Arrhenius definition of base: a compound
that produces hydroxide ions (OH-) when
dissolved in water.
 Let’s write the dissociation reaction for the NaOH
example.
NaOH + H 2 O  Na + + OH -
ARRHENIUS ACIDS & BASES
Acids are hydrogen-containing compounds
that ionize to yield hydrogen ions in aqueous
solution...
Bases are compounds that ionize to yield
hydroxide ions in aqueous solution...
BUT, NH 3 is a base! Arrhenius’ theory doesn’t
hold up in every case, so...
BRONSTED-LOWRY ACIDS AND BASES
An acid is a hydrogen-ion donor, and a base
is a hydrogen-ion acceptor.
Example:
NH 3(aq) + H 2O(l)  NH 4+ (aq) + OH -(aq)
Analyze the compounds as they react. What
happens during the reaction?
 NH 3 accepts an H + to become NH 4 +
 H 2 O donates an H + to become OH -
ACID-BASE PAIRS
 Previous Example:
NH 3 (aq) + H 2 O(l)  NH 4 + (aq) + OH - (aq)
 According to the Bronsted-Lowry theory:
 An acid has a conjugate base.
 Likewise, a base has a conjugate acid.
 We refer to them as conjugate acid-base pairs.
The pair differs only by a SINGLE hydrogen.
 Example: NH 3 and NH 4 + , H 2 O and OH -
APPLICATION OF THE BRONSTED-LOWRY
THEORY
H 2SO 4 + H 2O  H 3O + + HSO 4-
1) Label the acid, base, conjugate acid, and
conjugate base.
2) Write conjugate acid-base pairs.