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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
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Two sp 2 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 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
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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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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
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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