Acid / Base Neutralization
Reactions
Chapter 4b:
Acid /Base
Neutralization
Reactions
• Combination of acid + base to form water + salt
HCl (aq) + NaOH (aq) → H2O + NaCl (aq)
(acid)
(base)
(water)
(salt)
• Based on swapping of H+ and OH– to form water
H Cl (aq) + Na OH (aq) → H OH + Na Cl (aq)
Chem 111
Dr. Gentry
Acid / Base Neutralization Reactions
Acid: A substance that provides H+ ions in water.
HCl, HNO3, H2SO4, H3PO4
H Cl (aq)
→ H+
+
Cl–
Base: A substance that provides OH- ions in water.
NaOH, KOH, Ba(OH)2
Acid / Base Neutralization Reactions
A substance that provides H+ ions in water.
Acid:
Base: A substance that provides OH- ions in water.
When combined: acid & base form water & “salt”
HCl(aq) + NaOH(aq) → H2O + NaCl (aq)
acid:
Na OH (aq) → Na+
+
OH–
Strong & Weak Acids
Strong Acids: completely dissociate in water
HCl
HNO3
H2SO4
H+ + Cl‒
H+ + NO3‒
2H+ + SO4‒2
(Hydrochloric acid)
(Nitric acid)
(Sulfuric acid)
H Cl (aq)
→ H+
base: Na OH (aq) → Na+
+
Cl–
+
OH–
Strong & Weak Bases
Strong Bases: completely dissociate in water
NaOH
KOH
Ca(OH)2
Na+ + OH‒
K+ + OH‒
Ca+2 + 2OH‒
(Sodium hydroxide)
(Potassium hydroxide)
(Calcium hydroxide)
Weak Acids: only slightly dissociate in water
HC2H3O2
(Acetic acid)
H + + C 2H 3O 2‒
(Acetate ion)
H2CO3
(Carbonic acid)
H+ + HCO3‒
(Bicarbonate ion)
HF
(Hydrofluoric acid)
Weak Bases: only partially dissociate in water
NH3 + H2O
(Ammonia)
NH4+ + OH‒
(Ammonium ion)
H+ +
F‒
(Fluoride ion)
1
What About Excess H+ and OH– ?
Net Ionic Eqn’s for Strong Acids/Bases
Molecular Equation
Molecular Equation
H Cl(aq) + Na OH (aq) → H2O(l) + Na Cl(aq)
HCl (aq)
H+ (aq) + Cl‒ (aq)
NaOH (aq) Na+ (aq) + OH‒ (aq)
NaCl (aq) Na+ (aq) + Cl ‒ (aq)
Ionic Equation
H+ (aq) + Cl‒ (aq) + Na+ (aq) + OH‒ (aq)
→ H2O(l) + Na+ (aq) + Cl‒ (aq)
Net Ionic Equation
H+ (aq) + OH‒ (aq)
Ionic Equation
[ H+ + Cl‒ ] + [Na+ + OH‒ ] → H2O + [ Na+ + Cl‒ ]
• If equal moles of HCl and NaOH, then all H+ and OH–
combine to form water
• But if HCl and NaOH are different, then excess acid or
base will leave behind excess H+ or OH– in the solution
Use pH to Describe the H+ and OH–
→ H2O(l)
Net Ionic Eqn’s for Weak Acid or Base
Molecular Equation
HC2H3O2 (aq) + NaOH (aq) → H2O (l) + NaC2H3O2 (aq)
HC2H3O2 (aq)
NaOH (aq)
NaC2H3O2 (aq)
H Cl(aq) + Na OH (aq) → H2O(l) + Na Cl(aq)
pH
14
pH > 7
Low H+
Conc.
(if weak acid/base, then leave as is)
Na+ (aq) + OH‒ (aq)
Na+ (aq) + C2H3O2 ‒ (aq)
Measure of How Much H+ is Present
(i.e. the concentration of H+)
Strong Acid – completely dissociates
pH
Will have a large H+ concentration
… a low pH
Ionic Equation
HC2H3O2 (aq) + Na+ (aq) + OH‒ (aq)
→ H2O(l) + Na+ (aq) + C2H3O2‒ (aq)
Net Ionic Equation
pH < 7
High H+
Conc.
HC2H3O2 (aq) + OH‒ (aq) → H2O(l) + C2H3O2‒ (aq)
Weak Acid – only partially dissociates
HC2H3O2
pH
H+ and OH‒ Offset Each Other
14
pH
= ‒ log
pH is the negative power of 10 of the molarity)
[H+ ] = 10 –4 M
[H+]
[OH‒]
Square brackets are concentration of H+
in units of molarity
Basic (alkaline),
High OH‒
Conc.
pH = +4
Low H+
Conc.
7
10‒3
0.001
=
M
0.0000000001 = 10‒10 M
pH > 7
High amount of OH‒
Low amount of H+
Neutral water,
pH = 7
Equal amount of H+ and OH‒
pH = + 4 ⇒ pOH = +10
[H+]
0.0000001
= 10‒7 M
H + + C 2H 3O 2‒
Will have a low H+ concentration
… a higher pH
0
Formal Definition of pH
[H+]
H+ + Cl‒
HCl
7
pH
+7
+3
+10
Low OH‒
Conc.
High H+
Conc.
Acidic,
pH < 7
Low amount of OH‒
High amount of H+
0
2