1

Double Bond: C2H4

An sp 2 hybridized C atom has one

electron in each of the three sp 2 lobes

Top view of the sp

2 hybrid

Side view of the sp 2 hybrid

+ the unhybridized p orbital

2

Two sp 2 hybridized C atoms plus p -orbitals in

proper orientation to form a C=C double bond

Double Bond: C2H4

3

Double Bond: C2H4

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

2 hybrids is designated as a bond

The other portion of the double bond, resulting from the side-on overlap of the p orbitals, is designated as a bond

4

A 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 bonds

Note that a triple bond consists of one and two bonds

Triple Bond: C2H2

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CHAPTER 10 Reactions 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– anions in aqueous solutions

These two statements represent the Arrhenius theory of acids and bases

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The BrØnsted-Lowry Theory This 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 hydronium ionhydronium ion

10

The BrØnsted-Lowry Theory Acid-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 acid-base pairsconjugate acid-base pairs

Such conjugate pairs will exist for each acid-base reaction

HF(aq) + H2O(l) H3O+(aq) + F–(aq)

acid base HF is a weak acid and it does not

ionize completely in aqueous solutions This 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 acid Increase the total charge by 1

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

H2O

CH3COOH

NH3

CH3COO–

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Conjugate Acid-Base Pairs

acid1

base2 HF is a weak acid and ionizes only slightly

It 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 H2O

H3O+(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 bases Weak 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 taste Don’t taste them in the lab !!!

They change the colors of many indicators Acids turn blue litmus to red Acids turn bromothymol blue

from blue to yellow

They react with metals to generate hydrogen gas, H2

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Displacement Reactions Displacement 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, Mn, Zn, Fe, Co, Ni, Pb,Li, K, Ca, Na, Mg, Al, Mn, Zn, Fe, Co, Ni, Pb, 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 Series The 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)