The solubility of gases in water usually decreases with temperature see Table 11'2, page 611, for ex

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• The solubility of gases in water usually
  decreases with temperature (see Table 11.2, page
  611), for example

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• The gases in air are not very soluble in water
  under ordinary pressure
• The solubility increases as the pressure is
  increased

The amount of gas that dissolves in water
increases as the pressure is raised.
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How an increase in pressure increases the
solubility of a gas in a liquid. (a) At some
specific pressure, an equilibrium exists between
the vapor phase and the solution. (b) An increase
in pressure puts stress on the equilibrium. More
gas molecules dissolve than are leaving the
solution. (c) More gas has dissolved and
equilibrium has been restored.
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Got the Bends?
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• For gases that do not react with the solvent,
  Henrys law or the pressure-solubility law
  applies
• The concentration of a gas in a liquid at any
  given temperature is directly proportional to the
  partial pressure of the gas over the solution

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The solubility of O2(g) at 25 degree Celsius is
8.2 mg/L when the partial pressure is 152
torr.What is the solubility of this gas at 25
degrees Celsiuswhen the partial pressure is 800
torr?
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• Gas molecules with polar bonds are much more
  soluble in water than nonpolar molecules like
  oxygen and nitrogen
• Some gases have increased solubility because they
  react with water
• For example

Carbonic acid
bicarbonate
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• Molar concentration or molarity, mol/L, is
  convenient for the stoichiometry of chemical
  reactions in solutions
• Two other temperature-intensive concentrations
  are common
• Percent Concentrations
• Also called percent by mass or percent by weight
• This is sometimes indicated (w/w) where w
  stands for weight

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• The (w/w) is often omitted
• Concentrations are sometimes reported as percent
  by mass/volume of (w/v)
• Percentages are parts per hundred (pph)
• Other concentrations include parts per million
  (ppm) and parts per billion (ppb)
• 1 ppm 1 g component in 106 g mixture
• 1 ppb 1 g component in 109 g mixture

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w/w problem
You analyzed 5 grams of apple sauce (the
solution) and Found it contained 0.3 mg of DDT
(the solute), a pesticide. Express the
concentration of DDT in apple sauce in Percent
(pph)ppt ppmppb
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w/v problem
You analyzed 10 mL of blood (the solution)
and found it contained 16.0 µg of hemoglobin
(the solute) Express the concentration of
hemoglobin in blood in (this is just an
examplenot the true concentration of hemo in
blood!) Percent (pph)ppt ppmppb
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• The number of moles of solute per kilogram
  solvent is called the molal concentration or
  molality (m)
• Dont confuse molality and molarity

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You need to make a 0.300 molal (m) solution of
sodium chloride. How many grams of NaCl would
have to be dissolved in 1600.0 g of water to
prepare the solution of this molality?
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A certain sample of dilute hydrochloric acid,
HCl, is 5.0 (notice, the w/w or w/v has been
omittedso when in doubt, assume w/w). Calculate
the molality of this solution.
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• With water as the solvent, the molality
  approaches the molarity as the solution becomes
  more dilute
• Colligative properties depend mostly on the
  relative populations of particles in mixtures,
  not on their chemical identities
• Solutes that cant evaporate from solution are
  called nonvolatile solutes
• All solutions of nonvolatile solutes have lower
  vapor pressures than their pure solvents

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• For dilute solution, Raoults law applies
• The change in vapor pressure can be expressed as

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Raoults law plot. When the vapor pressure of a
solution is plotted against the mole fraction of
solvent, the result is a straight line.

(a) With a high number of solvent molecules, the
rate of evaporation and condensation is
relatively high. (b) When some of the solvent is
replaced by a nonvolatile solute, the rate of
evaporation and the vapor pressure decrease.
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At 25ºC, the vapor pressure of water is 23.8
torr.What is the vapor pressure of a solution
prepared bydissolving 65.0 g of C6H12O6 (a
non-volative solute)in 150 g of H2O?
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• When a solution is made from two components that
  can evaporate, the vapor contains molecules of
  each component
• Each component is described by Raoults law,
  using the labels A and B

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• For an ideal, two-component solution of volatile
  components

The vapor pressure of an ideal, two-component
solution of volatile components (A and B).
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• Solutes affect the boiling and freezing point of
  solutions (relative to the pure solvent)

Phase diagrams for water and an aqueous solution
(not to scale). (a) Phase diagram for pure water.
(b) Phase diagram for an aqueous solution of a
nonvolatile solute.
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• The increase in boiling point is called the
  boiling point elevation
• The decrease in freezing point is called the
  freezing point depression
• Simple expressions relate the molality (m) to the
  temperature change

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• Table 14.3 (page 624) lists a number of boiling
  point elevation and freezing point depression
  constants
• These include