Considering the neutralization with a strong
monohydroxy base, what volume of 5.00 M
sulfuric acid is needed to create 2.85x1024 water
molecules?
Solubility and the Dissolving
Process
Solubility and Polarity
• Solubility – the ability of one substance to
dissolve into another at a given temperature
and pressure;
– expressed in terms of the amount of solute that
will dissolve in a given amount of solvent to
produce a saturated solution.
• Polar compounds tend to dissolve in other
polar compounds and nonpolar dissolve in
other nonpolar compounds.
Solubility and Polarity
• “Like dissolves Like”
• Miscible – describes two or more liquids that
are able to dissolve into each other in various
proportions.
• If two substances are immiscible, than they
will not mix together.
Solubilities of Solids
• The greater the surface area, the faster the
dissolving process.
• Dissolving only takes place at the surface of
substances. The solvent cannot penetrate the
solute, which make it take longer to dissolve
bigger “chunks”
• Shaking will also increase the speed. Why?
Temperature
• Solubilities of solids generally increase with
temperature.
• Increasing the temperature increases the
speed of the molecules which increases the
number of collisions. This speeds up the
solvent’s ability to dissolve the solute.
Breaking Down an Ionic Compound
• The dissolving of an ionic compound involves a unique
factor
– The separation of ions from the lattice into individual dissolved
ions.
• Dissociation – the separating of a molecule into simpler
molecules, atoms, radicals, or ions.
• If water is the solvent then the dissociation involves
hydration.
• Hydration – the surrounding of the dissociated ions by
water molecules.
Enthalpy and Entropy
• The dissociation process takes a large amount of
energy to rip apart the lattice.
• A large positive enthalpy change, ________, the
water then surrounds it which has a large
negative ΔH which nearly cancel out.
• As ions are scattered and broken apart, the
entropy ____________. Then the water
surrounding and reorganizing the ions
__________ the entropy, nearly cancelling out.
Enthalpy and Entropy
• The net result of all of the enthalpy and
entropy changes that accompany the
dissolving process determines the solubility of
an ionic solid.
• This study gave us our solubility rules.
– Tells is substances are soluble or insoluble in
water.
– Other solvents may be used if needed.
Saturation
• When the maximum amount of solute is
dissolved in solution, the solution is said to be a
saturated solution.
• If more can be added than is it a unsaturated
solution.
• Unsaturated Solution – a solution that contains
less solute than a saturated solution and that is
able to dissolve addition solute.
Exceeding Solubility
• A supersaturated solution is a solution
holding more dissolved solute than what is
required to reach equilibrium at a given
temperature.
• How can we coax the solvent to take in more
solute?
Equilibrium
• Solubility Equilibrium – the physical state in
which the opposing processes or dissolution and
crystallization of a solute occur at equal rates.
• The ions are leaving the solid surface at the same
rate as ions are also returning to the pile of
excess solute at the bottom of the solution.
• Gases can also be dissolved in liquids
– i.e. soda
Pressure and Temperature
• Henry’s Law states that the solubility of a gas
increases as the partial pressure of the gas on
the surface of the liquid increase.
• When you open a bottle of soda the pressure
is released and the solubility decreases,
allowing the gases to escape and making your
soda go “flat”
Temperature
• Warm soda has less CO2 dissolved in the liquid
which also gives it a flat taste.
• Gases are less soluble in a liquid of higher
temperature because the increased molecular
motion in the solution allows gas molecules to
escape their loose arrangement with the
solvent molecules.
– They Break Free
Concept Check
• Why is ethanol miscible in water?
• Why do sugar cubes dissolve more slowly in water than
granulated sugar?
• What factors are involved in determining the solubility
of an ionic salt?
• You keep adding sugar to a cold cup of coffee. You stir
it by eventually you notice sugar on the bottom.
Explain why no more sugar dissolves.
Conductivity
• Some substances have the ability to conduct
an electric current. This depends on whether
or not it contains charged particles that are
able to move freely around the solution.
• An electrolyte is a substance that dissolves in
water to give the solution the ability to
conduct an electric current.
Conductivity
• A nonelectrolyte is a liquid or solid substance
that does not allow the flow of an electric
current, either in solution or in its pure state,
such as water or sucrose.
• Ionic salts dissociate into their individual
charged ions that move around the solution
freely. Would this be an electrolyte or a
nonelectrolyte?
Acids / Bases
• Strong acids COMPLETELY dissociate in water,
forming the hydronium ion (H30+(aq))
– This makes all strong acids VERY good electrical
conductors
– Weak acids are less conductive but still dissociate
to an extent.
• Strong bases COMPLETELY dissociate in water,
forming the hydroxide ion (_____________)
– This makes strong bases also very good electrical
conductors.
Water and Electricity
• Sea water is a great conductor. Why?
• Tap water is also very good because it is not
distilled (still contains ions and minerals).
– Do not use electrical devices by water 