Something about Water

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Something about Water
Cool Water sung by Frankie Laine wirtten by B.
NOLAN 1989
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Is water a conserved quantity on earth?
The water cycle, what is it?
Sources of Water

• Oceans 97.45
• Ice caps, glaciers and ground water 2.59
• Lakes, streams, ponds atmosphere 0.014

The purity of potable water?
The chemical properties of water
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Heat of Formation
1/2 O2 H2 -gt H2O DH -241.818 kJ/mole
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Heat of Vaporization In order to vaporize water,
40.656kJ/mol of heat must be added to the liquid.
H2O(l, 298K, 1atm) -gt H2O(g, 298K, 1atm) DH
40.656 kJ/mole
torr
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This is reasonable since the water molecules are
attracted to each other by various forces not the
least of which is hydrogen bonding. In order to
break these forces, liberating the water
molecules into the gas phase, energy must be
added to the system. Because of liquid water's
unique structure this energy is greater than for
many liquids. We may represent this reaction by
the following equation now showing not only mass
and charge balance (everything is neutral here),
but also energy as well.
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Heat of Fusion (Freezing) H2O(l, 273.15K, 1atm)
-gt H2O(s, 273.15K, 1atm) DH 6.008 kJ/mole To
freeze liquid water 6008 J/mole must be removed.
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Heat Capacity 1 calorie/gram water at 14.5-15.5
C 75.29 J/mol K The relationship between the
heat capacity, Cp, and the amount of heat added
to water over a temperature difference, DT Tf -
Ti, is given by DH Cp/DT
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Phases of Water A normal liquid has a phase
diagram shown next.
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Phase Diagram for typical substance
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When an ordinary substance freezes it generally
becomes more dense, but when water freezes it
becomes less dense. Thus, ice floats on liquid
water. The expansion of ice over the volume
occupied by the liquid means that, when
constrained, it may exert a powerful force.
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Phase Diagram for Water
Supercritical water
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Water
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Polywater
In the 1970's some scientists published a paper
stating that they had found a new stable phase of
water a polymeric form they called "polywater."
A number of papers were written on the subject
including theories of its structure. A question
arose "If polywater indeed existed as a stable
form why was not all water polywater?" To answer
this we have to understand concepts of stability
and equilibrium.
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In Kurt Voneguts short story Cats Cradle a mad
scientist produces Ice Nine which is a stable
form of solid water. Ice Nine is released into
the oceans and causes the water on earth to
convert to this stable form and freeze. It is the
end of civilization as we know it. Vonegut's
story is theoretically correct and for good
reason his brother is a physical chemist and
knows about stability and the tendency of systems
toward equilibrium.
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Waters Ability to Dissolve Ionic Substances
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Coulombs Attraction between Na and Cl- in vacuum
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Hydrogen Bonding
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Water Mediates the effect of Coulombs in Vacuo
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Acids Bases
The not so strange story of extreme
hyperventilation. Acid and base properties in
blood.
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Al Vines Submersible, Alvin, explores deep sea
vents
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The Strange Case of Hydrothermal Vents on the
Ocean Floor and the Origin of Life. Vents on the
ocean floor make for an extreme environment where
water is in a supercritical region. The
temperatures and pressures are very high. Here
water acts in a different way, its density being
40 of the density of water at room temperature
and it is a much less polar liquid. That means
the solubility of molecules and ions is changes.
The structure of water is also affected. There is
life in this extreme region and that life has
evolved under very different circumstances than
we might imagine life evolving on the surface of
the earth. Here, in this extreme environment, the
food of b biological life is nitrogen, hydrogen
sulfide,k hydrogen, and oxygen-elementary
chemical forms rather than complex molecule like
carbohydrates and protein. How does this occur?
What chemical processes are involved? And what
are the implications about evolution?
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The Acid-Base Nature of Water Water defines what
is meant by neutral from an acid-base view point.
Water (in water) breaks up, or dissociates, into
two components H and OH- according to H2O lt--gt
H OH- where the double arrow signifies that
both dissociation and recombination occur at
equilibrium. Now if H is acid and OH- is base we
obviously have a neutral solution by definition.
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A chemical equation is an equation showing the
conservation of atomic species, mass and charge.
Thus, there are equal amounts of the positive and
negative species on the right to make a neutral
system. Since this resulted from the species on
the left (undissociated water) which had no
charge the charge is balanced in the reaction.
Since we started with two H and one O on the left
(the beginning of the reaction) we end up with
the same numbers.
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Some Simple Acids and Bases

• H2O, HOH both an acid and a base. 2H2O -gt H3O
  OH-

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Some Simple Acids and Bases

• H2O, HOH both an acid and a base. 2H2O -gt H3O
  OH-
• HCl hydrochloric acid HCl H2O -gt H3O Cl-

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Some Simple Acids and Bases

• H2O, HOH both an acid and a base. 2H2O -gt H3O
  OH-
• HCl hydrochloric acid HCl H2O -gt H3O Cl-
• NaOH sodium hydroxide NaOH H2O -gt Na OH-
  H2O

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Some Simple Acids and Bases

• H2O, HOH both an acid and a base. 2H2O -gt H3O
  OH-
• HCl hydrochloric acid HCl H2O -gt H3O Cl-
• NaOH sodium hydroxide NaOH H2O -gt Na OH-
  H2O
• HCOOH formic acid (from the distillation of
  ants!) HCOOH H2O -gt HCOO- H3O

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Some Simple Acids and Bases

• H2O, HOH both an acid and a base. 2H2O -gt H3O
  OH-
• HCl hydrochloric acid HCl H2O -gt H3O Cl-
• NaOH sodium hydroxide NaOH H2O -gt Na OH-
  H2O
• HCOOH formic acid (from the distillation of
  ants!) HCOOH H2O -gt HCOO- H3O
• H3CCOOH acetic acid (sour component of vinegar)
  H3CCOOH H2O -gt H3COO- H3O

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Some Simple Acids and Bases

• H2O, HOH both an acid and a base. 2H2O -gt H3O
  OH-
• HCl hydrochloric acid HCl H2O -gt H3O Cl-
• NaOH sodium hydroxide NaOH H2O -gt Na OH-
  H2O
• HCOOH formic acid (from the distillation of
  ants!) HCOOH H2O -gt HCOO- H3O
• H3CCOOH acetic acid (sour component of vinegar)
  H3CCOOH H2O -gt H3COO- H3O
• NH4OH ammonium hydroxide a base (common kitchen
  cleaner component) NH4OH(aq) -gt NH4(aq)
  OH-(aq)

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Some Simple Acids and Bases

• H2O, HOH both an acid and a base. 2H2O -gt H3O
  OH-
• HCl hydrochloric acid HCl H2O -gt H3O Cl-
• NaOH sodium hydroxide NaOH H2O -gt Na OH-
  H2O
• HCOOH formic acid (from the distillation of
  ants!) HCOOH H2O -gt HCOO- H3O
• H3CCOOH acetic acid (sour component of vinegar)
  H3CCOOH H2O -gt H3COO- H3O
• NH4OH ammonium hydroxide a base (common kitchen
  cleaner component) NH4OH(aq) -gt NH4(aq)
  OH-(aq)
• H2NCH2COOH glycine, an amino acid, one of the
  building blocks of life

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Arrhenius Df. of Acid Base

• An acid is a substance in water that donates H
• A base is a substance in water that donates HO-

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Example

• HCl(aq) --gt H(aq) Cl-(aq)
• NaOH(aq) --gt Na(aq) OH-(aq)

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Bronsted-Lowry Df. of Acid Base

• An acid is any substance that can donate a
  proton,
• H, to any other substance.
• A base is any substance that can accept a proton,
• H, from any other substance.

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What makes a Strong Acid?
A proton bound to a more electronegative
atom will be more likely to ionize and therefore
be a stronger acid relative to a proton bound to
a less electronegative atom.
A proton bound to groups where electron
delocalization occurs will be a stronger
acid than a proton bound to groups where
less delocalization occurs.
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Why Acids and Bases? Who Cares?
Consider the fact, that crops will not grow
properly if the soil is too acid, or water will
not support life if the water is too acid.
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Why Acids and Bases? Who Cares?
Generally, the soil in New England is acidic and
needs lime (CaCO3) get it more basic. Due to acid
rain, rivers and ponds in New England are often
acidic. Not as acidic as vinigar, but close!
Sometimes, people have limed ponds!
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Why Acids and Bases? Who Cares?
Consider the fact, that among other things, we
are made up of proteins, and proteins are made up
of amino acids. An amino acid is both an acid
and a base!
L-Arginine
acid
base
base
base
acid
base
acid
base
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DNA Structure
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A Base-Pair showing H-bonds
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Urea One of the First Synthetic Organic Chemicals
base
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Acids Bases

• Acids Bases
• Classical Definition
• Generalized Acids and Bases
• acids and conjugate bases
• 2. pH Scale pH -LogH
• 3. pKa and pKb pK -Log(K)
• 4. Strong and Weak Acids and Bases
• equilibrium constant pKa pKb

X X X
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Equilibrium in Acids and Bases
H3CCOOH acetic acid (sour component of
vinegar) H3CCOOH H2O -gt H3COO- H3O
Ka(T) H3COO- H3O /H3CCOOH 1.8 x 10-5
moles/liter
The concentrations must adjust in order that this
expression yield the equilibrium constant, Ka(T).
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QuestionWhat signifies a Strong Acid, or a
Strong Base?
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Answer
The size of the equilibrium constant, Ka or Kb
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QuestionIs Acetic Acid a Strong Acid, or a
Weak Acid?
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Answer
The size of the equilibrium constant, Ka, will
tell us. Ka H3COO- H3O /H3CCOOH 1.8 x
10-5 moles/liter Since Ka 1.8 x 10-5
moles/liter ltlt 0 this is a weak acid.
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Now for a new acid/base concept
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Lewis Acids and Bases
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Lewis Acids and Bases
H3O NH3 -gt NH4 H2O acid base
acid base BF3 NH3 -gt
F3B-NH3 acid base complex AlCl3
NH3 -gt AlCl3-NH3 acid base
complex
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The classic view of an acid base reaction is the
neutralization of H3O by OH- to form water H3O
OH- -gt 2 H2O G. N. Lewis looked at this in a
more general way. The proton, H, likes to accept
an electron. Therefore, a Lewis Acid is a
compound that accepts an unshared pair of
electrons. Using this chemical idea we may
classify acids and their conjugate bases as the
previous example showed.
H3O NH3 -gt NH4 H2O acid base
acid base BF3 NH3 -gt
F3B-NH3 acid base complex AlCl3
NH3 -gt AlCl3-NH3 acid base
complex
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Buffers
A buffer is a solution made of an equal molar
mixture of an acid and its conjugate base. It has
the property that it stabilizes the pH to
additions of either acid or base.
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