Chapter 4: Types of Chemical Reactions Goals: • To be able to predict chemical reactivity. • To know how to synthesize specific compounds.
Jan 07, 2016
Chapter 4: Types of Chemical Reactions
Goals:
• To be able to predict chemical reactivity.
• To know how to synthesize specific compounds.
Types of Reactions
• Acid-Base: proton-transfer• Oxidation-Reduction: electron-transfer• Precipitation: formation of insoluble salts• Gas Forming• Organic:
– Substitution– Addition– Elimination
Reactions in Aqueous Solution
Unless mentioned, all reactions studied this and next week occur in aqueous solution.
Electrolytes
Strong Electrolytes: solute breaks apart to give ions in solution.
NaCl Na+ + Cl-
Weak Electrolytes: solute partially breaks apart to give ions.
CH3CO2H CH3CO2- + H+ happens less than 5%
Nonelectrolytes: no ions formed.
CH3CH2OH
Brønsted-Lowery Acid-Base Definitions
• An acid is a substance that donates a proton (H+) to a base
• A base is a substance that accepts a proton (H+) from an acid
Brønsted-Lowery Definitions• acid: donates a proton (H+) to a base
• base: accepts a proton (H+) from an acid
• Acid-base reactions can be reversible:reactants products or products reactants
Brønsted-Lowery Definitions• An acid is a substance that donates a proton (H+)
to a base
• A base is a substance that accepts a proton (H+) from an acid
• Acid-base reactions can be reversible:reactants products or products reactants
Important Acids and BasesStrong Acids:
HCl hydrochloric
HBr hydrobromic
HI hydroiodic
HNO3 nitric
H2SO4 sulfuric
HClO4 perchloric
Weak Acid:
CH3CO2H acetic
Any other acids are WEAK
Strong Bases:
LiOH lithium hydroxide
NaOH sodium hydroxide
KOH potassium hydroxide
Ca(OH)2 calcium hydroxide
Ba(OH)2 barium hydroxide
Weak Base:
NH3 ammonia
STRONG acids in water: 100% of acid molecules form ions:
HCl(aq) + H2O(l) H3O+(aq) + Cl-(aq)
H3O+ is
hydronium ion
WEAK acids in water, ~5% or less of acid molecules form ions (acetic, H3PO4, H2CO3)
Polyprotic Acidsmultiple acidic H atoms
H2SO4 H+ + HSO4-
HSO4- H+ + SO4
2-
Not all H’s are acidic:
CH3CO2H
If H3PO4 reacts as an acid, which of the following can it not make?
• 1. H4PO4+
• 2. H2PO4-
• 3. HPO42-
• 4. PO43-
If C2O42- reacts in an acid-base
reaction, which of the following can it not make?
• 1. H2C2O4
• 2. HC2O4-
• 3. 2 CO2
Acid-Base Reactions
Strong Acid + Strong Base
HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l) acid base “salt” water
Acid-Base Reactions
Diprotic Acids or Bases
H2SO4(aq) + NaOH(aq)
H2SO4(aq) + Ba(OH)2(aq)
HCl(aq) + Ba(OH)2(aq)
Acid-Base Reactions
Strong Acid + Weak Base
HCl(aq) + NH3(aq) NH4Cl(aq)
Acid-Base Reactions
Weak Acid + Strong Base
HCN(aq) + NaOH(aq) NaCN(aq) + H2O(l) acid base “salt” water
Net Ionic Equations
HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)
What really happens:
H+(aq) + OH-(aq) H2O(l)
Sodium ion and chloride ion are “spectator ions”
Reactions involving weak bases
HCl(aq) + NH3(aq) NH4+(aq) + Cl-(aq)
Net-Ionic Equation:
NH3(aq) + H+(aq) NH4+(aq)
CH3CO2H(aq) + NaOH(aq)
• 1. CH3CO2H2+(aq) + NaO(aq)
• 2. CH3CO2-(aq) + H2O(l) + Na+(aq)
• 3. CH4(g) + CO2(g) + H2O(l)
HCN(aq) + NH3(aq)
• 1. NH4+(aq) + CN-(aq)
• 2. H2CN+(aq) + NH2-(aq)
• 3. C2N2(s) + 3 H2(g)
Solution Concentration: Molarity
• Molarity = moles solute per liter of solution
• 0.30 mol NH3 dissolved in 0.500 L
Concentration =
• Written like: [NH3] = 0.60 M
pH Scale• In pure water, a few molecules
ionize to form H3O+ and OH–
H2O + H2O OH– + H3O+
• In acidic and basic solutions, these concentrations are not equalacidic: [H3O+] > [OH–]basic: [OH–] > [H3O+]neutral: [H3O+] = [OH–]
pH Scale• Measure how much H3O+ is in a
solution using pH• pH < 7.0 = acidic• pH > 7.0 = basic• pH = 7.0 = neutral• Measure of H3O+ and OH–
concentration (moles per liter) in a solution
• As acidity increases, pH decreases
pH Scale• The pH scale is logarithmic:The pH scale is logarithmic:
100100 101022 log(10log(1022) = 2) = 21010 101011 log(10log(1011) = 1) = 111 101000 log(10log(1000) = 0) = 00.10.1 1010–1–1 log(10log(10–1–1) = –1) = –10.010.01 1010–2–2 log(10log(10–2–2) = –2) = –2
• pHpH = –log [H= –log [H33OO++]]
• pH if [HpH if [H33OO++] = 10] = 10–5–5? 10? 10–9–9? ?
Acidic or basic?Acidic or basic?
• pH if [HpH if [H33OO++] = 0.000057 M?] = 0.000057 M?
Finding [H[H33OO++] from pH] from pH
[H[H33OO++] = 10] = 10-pH-pH
What is [HWhat is [H33OO++] if pH = 8.9?] if pH = 8.9?
pH: Quantitative Measure of Acidity
• Acidity is related to concentration of H+ (or H3O+)
• pH = -log[H3O+]