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Double Bond: C2H4An sp2 hybridized C atom has one electron in each of the three sp2 lobes

Top view of the sp2 hybrid

Side view of the sp2 hybrid + the unhybridized p orbital

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Two sp2 hybridized C atoms plus p-orbitals in proper orientation to form a C=C double bond

Double Bond: C2H4

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Double Bond: C2H4

The portion of the double bond formed from the head-on overlap of the sp2

hybrids is designated as a σ bondThe other portion of the double bond, resulting from the side-on overlap of the p orbitals, is designated as a π bond

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A σ bond results from the head-on overlap of two sp hybrid orbitals

Triple Bond: C2H2

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The unhybridized p orbitals form two π bondsNote that a triple bond consists of one σ and two π bonds

Triple Bond: C2H2

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CHAPTER 10Reactions in Aqueous Solutions I: Acids, Bases, and Salts

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The Arrhenius Theory

Acids are substances that contain hydrogen and produce H+ cations in aqueous solutions

Bases are substances that contain a hydroxyl group and produce OH– anionsin aqueous solutions

These two statements represent the Arrhenius theory of acids and bases

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The BrØnsted-Lowry TheoryThis theory is more general than the Arrhenius theory

An acid is a proton donor (H+)A base is a proton acceptor

NH3(aq) + H2O(l) → NH4+(aq) + OH–(aq)

acidbase

Notice, that according to the Arrhenius theory NH3 is not a base

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The Hydronium Ion

The protons (H+) are never present in solution by themselves

Protons are always hydrated that is surrounded by several water molecules

We don’t know exactly how many

H+(aq) is really H(H2O)n+

Where n is a small integer

We normally write the hydrated hydrogen ion as H3O+ and call it the hydroniumhydronium ionion

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The BrØnsted-Lowry TheoryAcid-base reactions are the transfer of a proton from an acid to a base

NH3(aq) + HCl(aq) → NH4+(aq) + Cl–(aq)

acidbase

HCl(aq) + H2O(l) → H3O+(aq) + Cl–(aq)acid base

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Conjugate Acid-Base Pairs

Two species that differ by a proton are called conjugate acidconjugate acid--base pairsbase pairsSuch conjugate pairs will exist for each acid-base reaction

HF(aq) + H2O(l) → H3O+(aq) + F–(aq)acid baseHF is a weak acid and it does not ionize completely in aqueous solutionsThis reaction also proceeds in the reverse direction (it is reversible)

acid base

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Conjugate Acid-Base Pairs

To find a conjugated base:Add 1 proton (H+) to the acidIncrease the total charge by 1

To find a conjugated acid:Remove 1 proton from the baseDecrease the total charge by 1

H2OCH3COOH

NH3

CH3COO–

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Conjugate Acid-Base Pairs

acid1 base2

HF is a weak acid and ionizes only slightlyIt prefers to exist as HF(aq) rather than F–(aq)This means that F–(aq) has higher affinity to the proton than H2O (it holds the proton stronger)Another way to put it is to say that F–(aq) is a stronger base than H2OH3O+(aq) gives up the proton easier than HF(aq) and therefore it is a stronger acid than HF(aq) (it is more prone to loosing the proton)

acid2 base1

HF(aq) + H2O(l) H3O+(aq) + F–(aq)

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The BrØnsted-Lowry Theory

Important conclusion:Weak acids have strong conjugate basesWeak bases have strong conjugate acids

The weaker the acid or base, the stronger the conjugate partner

Another example: ammonia in water

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Properties of Acids

Solutions of acids have a sour tasteDon’t taste them in the lab !!!

They change the colors of many indicators

Acids turn blue litmus to redAcids turn bromothymol blue from blue to yellow

They react with metals to generate hydrogen gas, H2

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Displacement ReactionsDisplacement reactions occur when one element displaces another element from a compound:

Zn + H2SO4 → ZnSO4 + H2

Not all the metals are capable of displacing hydrogen from an acid

Total and net ionic equations:

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Metal Activity Series

Active enough to displace hydrogen from an acid

Li, K, Ca, Na, Mg, Al, Li, K, Ca, Na, Mg, Al, MnMn, Zn, Fe, Co, Ni, , Zn, Fe, Co, Ni, PbPb,, H, Cu, Hg, Ag, Pt, AuCu, Hg, Ag, Pt, Au

Cannot displace hydrogen from an acid

More active

Less active

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Write reactions between the following metals and HCl solution. Write total and net ionic equations in each case

Fe, Na, Pt, Ni, Cu

Example 1

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Write reactions between the following metals and HCl solution. Write total and net ionic equations in each case

Fe, Na, Pt, Ni, Cu

Example 1 (continued)

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Metal Activity SeriesThe more active metal will always displace the less active metal from the solution of its salt:

Cu + 2AgNO3 → Cu(NO3)2 + 2Ag

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Write reactions between the following substances in aqueous solutions:

Zn + CuSO4

Hg + Fe(NO2)3

Mg + Hg(NO3)2

Al + Fe(NO3)3

Example 2

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Example 2 (continued)

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Assignments & Reminders

Go through the lecture notes

Read Chapter 10 completely

Read Section 4-10 of Chapter 4

Monday (10/31) and Tuesday (11/1) –lecture quiz #5 (Chapter 8)

Homework #5 is due by Monday (10/31)