Chapter 7.2 & 7.3: Solutions
• from 7.1, In a solution
– solute: stuff dissolved
– solvent: it’s dissolved in
• Called the universal solvent, because almost
everything dissolves in water (not because
our bodies are mostly water or the Earth
is 75% water)
• Water
– Polar compound: oxygen keeps the electrons a
little more than hydrogen does, so it has a little
bit of charge on each end
– “uneven distribution of electrons” … not equally
shared, so has charge
Dissolving
Process
• in water, the partial charge helps pull
molecules apart, making more room
for interactions between molecules
• breaking apart gives more surface area
for interactions between molecules
• stirring/shaking moves molecules away,
making more room for interactions
between molecules
• heating makes molecules move faster so
there’re more interactions between
molecules
Hydrogen Bonding
• Because water is polar, it forms
hydrogen bonds between atoms
• Not a bond within one molecule, e.g.
between the hydrogen and oxygen
• A bond between 2
atoms…hydrogen
of 1 water is
attracted to oxygen
of another because
water is polar.
Nonpolar compounds
• no partial charges
• “electrons evenly distributed” …
evenly spread out, so no charges
• e.g. oil
• Like Dissolves Like:
– Things only dissolve in similar solvents,
i.e. polar in polar and nonpolar in
nonpolar.
Solubility and Concentration
• Solubility: maximum amount of solute
that will dissolve at a particular
temperature and pressure
(quantitatively)
– also how well it dissolves in something
(qualitatively)
– depends on the strength of attraction
between atoms
• Concentration: actual amount dissolved
– g solute/100mL solvent (1 mL isn’t a lot, so
we use 100 mL)
– a lot: concentrated
– a little: dilute
Concentrations of solutions
• unsaturated: can hold more solute, holding
less than the maximum amount at that temp.
• saturated: can not hold any more, holding the
maximum amount at that temp.
• supersaturated: hold more than normal at that
temp (make by heating, adding solute and
then cooling)
• video:
http://www.youtube.com/watch?v=XSGvy2FPfC
w
• http://www.youtube.com/watch?v=HnSg2cl09PI
&feature=fvw
Factors affecting solubility
• Temperature: as temp of solvent goes
up, can hold more solid, but less
gas
• Pressure: as pressure goes up, can
hold more gas
• So…to dissolve more solid, increase
temperature
• To dissolve more gas, increase
pressure
Solubility Curves
• not in book
• show how much will
dissolve at a
certain temperature
• If you have a
concentration on
the line, it is
saturated. It is
holding the
maximum it can at
that temp
Solubility Curves
• If you have a concentration
above the line, it either
will not stay in solution,
because it is holding
more than the
maximum it can at that
temp. Or it will be
supersaturated.
• If you have a concentration
below the line, it is
unsaturated. It is
holding less than the
maximum it can at that
temp … you can still
add more solute.
Solubility Curves
• Note how the line for
a gas looks
different … as
temp goes up, the
gas molecules
move faster and
do not stay in the
solution.
• Sol. decreases as
temp. increases