Acids and Bases: Qualitative and
Quantitative Approaches
SCH4U1 Unit 5
Acids and Bases So Far…
Grade 10
• Nomenclature and formulas
• Properties of acids and bases
• Arrhenius definition (HX = acid; XOH = base)
Grade 11
• Brønsted-Lowry definition
• Strong vs weak, concentrated vs. dilute
• pH scale
• Acid-base titrations
Qualitative Properties of Acids
and Bases
Qualitative Properties of Acids and Bases
Acids
•
•
•
•
•
•
Soluble is water
Sour taste
Watery feel
Electrolyte
React w/ metals to make H2
Formed by non-metal
oxides + water (SO3 + H2O)
• Neutralize bases
• Turns litmus red
Bases
•
•
•
•
•
•
Soluble or insoluble
Bitter taste
Soapy feel
Electrolyte
No reaction w/ metals
Formed by metal oxides
+ water (Na2O + H2O)
• Neutralize acids
• Turns litmus blue
Chemical Definitions of Acids & Bases
1) Arrhenius Theory (1884)
Based on dissociation in water.
2) Brønsted-Lowry Theory (1923)
Based on proton (H+) transfer in reactions.
3) Lewis Theory (1923)
Based on electron pair transfer.
Acid-Base Key Terms
Electrolytes: compounds that dissociates or
ionizes when dissolved in water (e.g. NaCl)
100%
Na+ (aq) + Cl- (aq)
NaCl
Electrolytes conduct electricity when dissolved.
Water is a very weak electrolyte.
≈ 0%
H2O
no reaction
Strong Acid/Base: Acids or bases that ionize
(dissociate) 100%.
Strong Acids: HCl, HBr, HI, HNO3, HClO4, H2SO4* (1 H)
HBr(aq)
H+ (aq) + Br- (aq)
100%
Strong Bases: LiOH, NaOH, KOH, RbOH, CsOH (soluble)
Mg(OH)2, Ca(OH)2, Sr(OH)2, Ba(OH)2 (insoluble)
CsOH (s)
Cs+ (aq) + OH- (aq)
100%
All other acids or bases are weak.
Two Important Ions
• Hydronium (protonated water)
• Hydroxide (deprotonated water)
Polyprotic Acids
• Monoprotic: Acids containing only one
ionizable hydrogen (e.g. HCl).
• Diprotic: Acids containing two… (e.g. H2CO3)
• Triprotic: Acids containing three… (e.g. H3PO4)
Amphoteric: A substances capable of acting like
acids OR bases in BL acid-base reactions.
HSO4- (aq) + H2O ⇌
BL Acid
BL Base
HSO4- (aq) + H2O ⇌
BL Base
BL Acid
SO42- (aq) + H3O+ (aq)
CB
CA
H2SO42- (aq) + OH- (aq)
CA
CB
Quantitative Properties of Acids
and Bases
Quantitative Properties of Acids and Bases
Water itself never consists of “pure” H2O. Water
constantly undergoes autoionization to produce
these ions:
H2O (l)
H+ (aq) + OH− (aq)
or more accurately,
H2O + H2O (l)
H3O+ (aq)
+ OH− (aq)
base
conj. acid
conj. base
acid
Ion Product Constant of Water (Kw)
The equilibrium constant equation for this
autoionization process can be written as:
Kw = [H3O+][OH−] = 1.0 x 10-14 (at 25oC)
Therefore for “pure” water:
[H3O+] = [OH−] = 1.0 x 10-7 mol/L
So what really is an acid & base?!
Water undergoes autoionization in all aqueous
solutions. If an acid or a base is dissolved in water,
then [H3O+] ≠ [OH−], but the product of their
concentration always equals 1.0 x 10-14 or Kw.
In all aqueous solutions:
2H2O (l)
H3O+ (aq)
+ OH− (aq)
Kw = [H3O+][OH−] = 1.0 x 10-14
Defining Neutral, Acidic & Basic
For an aqueous equilibrium:
Solution is neutral:
[H3O+] = [OH−]
Solution is acidic:
[H3O+] > [OH−]
Solution is basic:
[H3O+] < [OH−]
Problem Solving with Strong Acids
and Bases
• Refer to the sample questions on quantitative
aspects of acids and bases.