ACIDS AND BASES : ACIDS AND BASES CHAPTER 10
COMMON ACIDS : COMMON ACIDS
COMMON BASES : COMMON BASES
BLOOD PLASMA pH = 7.4 (Buffer) : BLOOD PLASMA pH = 7.4 (Buffer)
OTHER APPLICATIONS : OTHER APPLICATIONS As catalysts for organic reactions
Our digestive system
stomach acid
pH = 1.6
IDENTIFYING ACIDS AND BASES : IDENTIFYING ACIDS AND BASES Multiple definitions
Arrhenius, Bronsted-Lowry, Lewis
A B-L acid is a chemical species capable of donating a proton (H+)
A B-L base is a chemical species capable of accepting a proton (H+)
B-L acid must have at least one H in its formula
IDENTIFYING ACIDS AND BASES : IDENTIFYING ACIDS AND BASES Classical: the neutralization reaction between the acid HCl and the base NaOH
HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)
Write in ionic form
H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) H2O(l) + Na+(aq) + Cl-(aq)
CONJUGATE ACIDS AND BASES : CONJUGATE ACIDS AND BASES Conjugate acid/base pairs
HCl/Cl-
acid/conjugate base
HO-/H2O
base/conjugate acid
The conjugate base is the deprotonated form of the acid
The conjugate acid is the protonated form of the base
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10_00-09UN.JPG : 10_00-09UN.JPG “hydronium ion”
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WATER AS AN ACID OR A BASE : WATER AS AN ACID OR A BASE With strong acid ‘HX’
HX + H2O -------? X- + H3O+
With strong base (carbonate)
H2O + CO3- -----? HO- + HCO3-
Water is a weak acid and a weak base
Water is an amphoteric substance
STRONG AND WEAK ACIDS AND BASES.....Table 10.3 : STRONG AND WEAK ACIDS AND BASES.....Table 10.3 Strong acids
HCl
hydrochloric acid
H2SO4
sulfuric acid
HNO3
nitric acid
HClO4
perchloric acid
STRONG ACIDS AND SOLUBILITY : STRONG ACIDS AND SOLUBILITY HCl(g) H3O+(aq) + Cl-(aq)
Strong acids are polar covalent compounds which completely dissolve.....dissociate.... in water
They are completely ionized in solution
Strong acids are strong electrolytes H2O
WEAK ACIDS : WEAK ACIDS CH3CO2H
acetic acid
NH4+
ammonium ion
HF
hydroflouric acid
WEAK ACIDS AND SOLUBILITY : WEAK ACIDS AND SOLUBILITY CH3CO2H(l) H3O+(aq) + CH3CO2-(aq)
Weak acids are also polar covalent compounds which only partially dissolve.....dissociate.... in water
Weak acids are weak electrolytes H2O
STRONG AND WEAK BASES : STRONG AND WEAK BASES Strong bases
KOH
potassium hydroxide
NaOH
sodium hydroxide
Ba(OH)2
barium hydroxide
(various Group 1 and 2 oxides)
STRONG BASES AND SOLUBILITY : STRONG BASES AND SOLUBILITY KOH(s) K+(aq) + HO-(aq)
Complete dissociation
But base, KOH, is an ionic compound H2O
WEAK BASES : WEAK BASES NH3
ammonia
HCO3-
bicarbonate
SO42-
sulfate
WEAK BASES AND SOLUBILITY : WEAK BASES AND SOLUBILITY NH3(g) NH4+(aq) + HO-(aq)
Only partially dissociated H2O
PATTERN....?? : PATTERN....?? The conjugate bases of strong acids are weak bases
The conjugate bases of weak acids are strong bases
The conjugate acids of strong bases are weak acids
The conjugate acids of weak bases are strong acids
PATTERN....?? : PATTERN....?? The conjugate bases of strong acids are weak bases
HCl/Cl-
The conjugate bases of weak acids are strong bases
H2O/HO-
The conjugate acids of strong bases are weak acids
CN-/HCN
The conjugate acids of weak bases are strong acids
NO3-/HNO3
QUANTIFYING ACIDS AND BASES : QUANTIFYING ACIDS AND BASES Ka and pH
Ka: THE ACID DISSOCIATION CONSTANT : Ka: THE ACID DISSOCIATION CONSTANT For any acid “HA”
HA(aq) + H2O(l) H3O+(aq) + A-(aq)
Ka = [H3O+][A-]/[HA]
Strong acids: Ka >> 1
Weak acids: Ka<< 1
(pKa) : (pKa) pKa = -log(Ka)
Strong acids
pKa < 0
Weak acids
pKa > 0
Ka and pKa are opposite
PREDICTING ACID-BASE REACTIONS : PREDICTING ACID-BASE REACTIONS For a reaction between any acid and any base to favor the products, the strengths of the acid and base as reactants must be greater than the strengths of their conjugates on the right
Simpler:
Ka > 1: strong acid ---? weaker c. acid
Ka < 1: weak acid ---? stronger c. acid
Slide 27 : Ka > 1
HCl + NaOH H2O + NaCl
CH3CO2H + NaOH H2O + NaCH3CO2
Ka < 1
HF + H2O H3O+ + F-
NH4+ + Cl- NH3 + HCl
LEVELING EFFECT : LEVELING EFFECT As long as either the acid or base is strong, the equilibrium lies to the right
Strong acid + strong base
Strong acid + weak base
Weak acid + strong base
Weak acid + weak base
SELF-IONIZATION OF WATER : SELF-IONIZATION OF WATER ....and pH