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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+]