Chapter 6.2
•Dissolving and
Solubility
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Making process of dissolving
FASTER!
• Many of same things that make
chemical reactions go faster –
• But DISSOLVING IS A
PHYSICAL CHANGE, NOT A
CHEMICAL CHANGE.
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Faster dissolving
• When a chunk of something
dissolves, you are just pulling it
apart into smaller bits (even
down to individual molecules or
ions)
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Faster dissolving
•
•
•
•
heat
stirring
shaking
smaller chunks (larger surface
area)
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In a solution, the solute molecules
are randomly distributed among
the solvent molecules
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Figure 15.1: Dissolving of
solid sodium chloride.
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• The solute is the
substance that
dissolves in a
solution.
• The solvent is
the substance
that dissolves
the solute to
make a
solution.
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Why is water such a great
dissolver (solvent) for other
substances?
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Water is polar...
It has a slightly negative “side” by
the oxygen atom, and slightly
positive “side” by the hydrogens.
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Water can dissolve ionic
compounds, and covalent
compounds that are polar
(have “slightly negative”
and “slightly positive”
parts).
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The interaction of polar water molecules with ions
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Representation of the polar hydrogen chloride molecule
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Chlorine hogs the electron blanket, leaving
hydrogen partially, but positively, exposed
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Figure 15.3: The ethanol
molecule contains a polar O—
H bond.
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molecule interacts strongly with
the polar O—H bond in ethanol.
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Soap
• The nonpolar side of a soap molecule is “attached”
(attracted to) nonpolar grease and oil, the polar side
hangs on to the water, and the dirt slips off your
hands and is pulled down the drain, trapped, along
with the water molecules, by that pesky soap
molecule!
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(a) non-polar gasoline and non-polar oil mix
(b) polar vinegar and nonpolar oil do not mix
(c) polar water and polar ethyl alcohol mix
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Figure 15.6: An oil layer
floating on water.
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For a more detailed explanation of why
polar and nonpolar materials can’t
dissolve each other:
• http://www.knoxnews.com/kns/science/a
rticle/0,1406,KNS_9116_1971484,00.ht
ml
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Saturated and Unsaturated
 A saturated solution contains the maximum
amount of solute that can dissolve.
Undissolved solute remains.
 An unsaturated solution does not contain all
the solute that could dissolve
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Supersaturated Solutions
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To see more of this
supersaturation experiment:
• http://www.csudh.edu/oliver/demos/sup
ersat/supersat.htm
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To see more exciting
supersaturation stuff, go to:
• Crystallization from
Supersaturated
Solutions of Sodium
Acetate
• Note, you may need to hit
“refresh” to get
demonstration started and
restarted.
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Molarity
• Concentration unit of a solution that
expresses moles of solute dissolved per
liter of solution.
• To make a 1 molar solution of a substance, put 1
mole of stuff into a container and add solvent (usually
water) up to the “1 liter” mark.
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Not
this
type
of
Mole
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Or
this
type
of
Mole
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Mole
• 6.02 x 1023 is a mole 602,000,000,000,000,000,000
• If you counted paper at the rate of one sheet
per second it would take you
19,089,294,774,226,281 years to count a
mole of paper.
• It is a big number because atoms are small.
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• A mole of sugar weighs about one half
pound but contains how many molecules of
sugar?
• 602,000,000,000,000,000,000
• 6.02 x 1023 molecules.
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Temperature and Solubility of
Solids
Temperature
0°
20°C
50°C
100°C
Solubility
KCl(s)
27.6
34.0
42.6
57.6
(g/100 g H2O)
NaNO3(s)
74
88
114
182
Does the solubility of solids seem to
increase or decrease with an increase in
the temperature?
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A. Why would a bottle of carbonated drink
possibly burst (explode) when it is left out
in the hot sun ?
B. Why would fish die in water that gets too
warm?
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Solutions
A. Gas in the bottle builds up as the gas
becomes less soluble in water at high
temperatures, which may cause the bottle
to explode.
B. Because O2 gas is less soluble in warm
water, the fish may not obtain the needed
amount of O2 for their survival.
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