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Announcements
Types of Chemical Reactions
Chapter 4 Goals:To be able to predict chemical reactivity.To know how to synthesize specific
compounds.
Types of Reactions
Acid-BaseOxidation-ReductionPrecipitationGas FormingOrganic:
Substitution Addition Elimination
Reactions in Aqueous Solution
Aqueous- solvent is water
Reactions we’ll discuss today/next week are in aqueous solution, unless otherwise noted Acid-Base Redox Precipitation
NaCl(aq)
Electrolytes
Strong: All of the solute comes apart to yield ions in solution
Dissolution of KMnO4
Weak: Some of the solute comes apart to yield ions
Nonelectrolytes: No ions formed
Let’s compare
NaCl Na Cl
CH3CH2OH
CH3CO2H CH3CO2 H
Electrolytes in the Human Body
Most important:Na+, Cl-, K+, Ca2+, Mg2+ ,HCO3
-, and PO43-, SO4
2-
Elevated K+ cardiac arrythmia
Decreased extracellular K+ paralysis
Excess extracellular Na+ fluid retention
Decreased plasma Ca2+ and Mg2+ muscle spasms
Acids and Bases
Theories- there’s lots of themOnes we’ll use in this course
Lewis (later) Brønsted-Lowry (now)
An acid is a substance that donates a proton (H+) to a base
The hydronium ion
Brønsted-Lowry Definitions
Acid= donates a proton (H+) to a baseBase= accepts a proton (H+) from an acidAcid base reactions are reversible (almost
always)
Brønsted-Lowry Definitions
Acid= donates a proton (H+) to a baseBase= accepts a proton (H+) from an acidAcid base reactions are reversible (almost
always)
Important Acids and Bases
Strong Acids
100% of acid molecules produce ions in water Dissociation vs. ionization
HCl(aq)H2O(l) H3O(aq)Cl (aq)
Weak Acids
Only a few acid molecules produce ions (≤5%)
Strong vs. Weak acid ionization
Polyprotic Acids
Polyprotic acids can donate more than one H+
Sulfuric acid
Citric acid (C6H8O7) : Not all H’s are acidic
H2SO4 H+ + HSO4-
HSO4- H+ + SO4
2-
Bases
Strong bases are hydroxide salts
For now, the only important weak base is NH3.
If H3PO4 reacts as an acid, which of the following can it not make?
1. H4PO4+
2. H2PO4-
3. HPO42-
4. PO43-
If C2O42- (oxalate ion) reacts in an acid-base reaction, which of
the following can it not make?
1 2 3
33% 33%33%1. H2C2O4
2. HC2O4-
3. 2 CO2
20
Acid Base Reactions
Acid Base Reactions
Strong Acid + Strong Base
HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l) acid base “salt” water
What do we get if we mix:
HBr + LiOH
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
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 ScaleIn 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 ScaleMeasure how much H3O+ is
in a solution using pHpH < 7.0 = acidicpH > 7.0 = basicpH = 7.0 = neutralMeasure of H3O+ and OH–
concentration (moles per liter) in a solution
As acidity increases, pH decreases
pH ScaleThe 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+]