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Unformatted text preview: ht to have been “disgusting walking mixtures.” Mixtures are cloudy
in appearance caused by the diffraction of light off of the separate regions of the mixture
(called the “Tyndall” effect). Even a mixture that looks homogenous (or advertised to be
so as in the case of milk) is in fact not a solution at all if it is cloudy.
Solubility refers to the amount of solute that can be dissolved in a solution at a
given temperature (and pressure if the solute is a gas). Notice that it does not speak to
how long it takes to dissolve, just the maximum amount. This means that things like
stirring, which makes things dissolve faster, will not influence solubility, just how long it
takes for the solvent to dissolve. The proof is trying to dissolve excess solute in a
solution that has already reached its solubility limit (called “a saturated solution”).
Temperature will influence solubility, as will pressure but only if the solvent is a gas.
The strongest influence of solubility is the nature of the solute and the solvent.
There is an old rule of thumb when discussing solubility; “like dissolves like.” Although
there are exceptions to this rule, generally speaking it means that polar solutes will
dissolve in polar solvents, and non-polar solutes will dissolve in non-polar solvents. This
provides interesting insight into substances, with a quick and convenient experiment to Dakota State University page 168 of 232 Experiment 16: Colligative Properties General Chemistry I and II Lab Manual test polarity. It also provides insight around the home. If you wanted to remove peanut
butter from a container, for example, you know that water will not work. Well, since
water will not work, it might be worth your while to try a non-polar solvent first, like
cooking oil. Once the peanut butter is gone, the cooking oil can be easily removed by
The presence of a solute in a solution will influence the properties of the solution.
That a solute will dissolve in a solvent to any extent means that the interaction between
the solvent and solute molecules (or ions) is more energetically favorable than the
interactions between the molecules (or ions) of the solute alone. In other words, the
presence of the solute will attract solvent to itself and hold onto it strongly. This results
in stronger intermolecular interactions in a solution than you would have in the solvent
alone. As such, certain properties will change.
These changes (freezing point depression, boiling point elevation and vapor
pressure depression) depend on the concentration of the solution, but not on the identity
of the solute. That is, the same concentration of any solute will produce the exact same
properties. We call these “Colligative properties.”
You will eventually want to use the Pasco temperature probe for this experiment.
Fill a large beaker with water. Place it somewhere on your bench where it can sit
undisturbed for the entire lab period. When the water se...
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