Chapter 15 Notes
15.1 What are solutions?
1) You might remember from the beginning of the year that solutions are _______________ mixtures. This means
solutions contain two or more substances, and are mixed enough to “look all the same”. Solutions do NOT
have to be liquids, bronze is a _______________solution and air is a _______________solution.
A) All solutions have two parts. The substance doing the dissolving is the _______________and the
substances being dissolved are the _______________. If you don’t know which is which, the substance
you have the most of overall is the _______________.
B) The most common solvent is _______________. It is so common and dissolves so many things that it is
often called “the universal solvent”. This is not entirely true, as only _______________solutes will
dissolve in water (we say they are _______________). Nonpolar substances will not dissolve in water (we
say they are _______________.)
2) Even when things are soluble in water, or any other solvent, different solutes will dissolve to different amount.
The actual amount (in grams) that will dissolve in 100 grams of a solvent is called the _______________.
When discussing the solubility of solutes, solutions are classified into 3 types: saturated, _______________,
and supersaturated.
A) A _______________solution has dissolved as much solute as it can. If you add sugar to iced tea and sugar
is just sitting at the bottom of the glass your iced tea is saturated for sugar.
B) An _______________solution can still dissolve more solute.
C) A _______________solution has been “tricked” into dissolving more solute than it should be able to. If
any more solute is added to a supersaturated solution, all the extra solute will undissolve
(_______________). This is how sugar crystal candy (rock candy) is made.
D) Because the solubility of solutions is dependent on _______________, chemists represent the amounts that
can be dissolved with a _______________curve:
How to read a solubility curve:
1) Temperature is the _______________ variable (the one you control). This is shown on the bottom of the graph.
You can warm up the solution with a stove or cool it down in a freezer.
2) The amount (in grams) of how much will dissolve at a particular temperature is the _______________ variable
(it depends on the temperature). This is shown on the left side of the graph. Notice this is for all the solutes in
_______________ grams of water.
A) If the temperature and amount of dissolved solute is on the line shown for that solute, then the solution is
_______________. For example, _______________ grams of NH3 in 100 grams of water will be a
saturated solution at 10 °C.
B) If the temperature and amount of dissolved solute is above the line, then the solution is _______________.
If the saturated solution of 70 grams of NH3 is very carefully heated, it will still have 70 grams of NH3 at
20 °C. As this amount is above the line, this would be a supersaturated solution.
C) If the temperature and amount of dissolved solute is below the line, then the solution is _______________.
An unsaturated solution could still dissolve more solute if it is added.
3) Temperature is not the only factor that will affect how much solute can dissolve. Particle size,
_______________, and agitation also have an effect.
A) Dissolving happens as the _______________ touches the solute and starts to pull it into pieces. This
happens only on the outside of the particles of the solute. One big chunk of solute has less outside
__________________________ than a lot of small pieces of solute. Thus, if the solute is crushed or
ground it will dissolve faster. This only works for dissolving _______________ in liquids.
B) Gases are affected by pressure. With high pressure a lot of gas can be squeezed into a little bit of space.
High pressures will help _______________ dissolve in a liquid, and low pressure will help
_______________ the gas from a liquid. This only works for dissolving a _______________ in a liquid,
and is why a carbonated beverage goes “flat” after it is opened.
C) When a _______________ dissolves in a liquid, it takes time for the liquid molecules to grab pieces of the
solid and float away. If the liquid is _______________, it speeds up the floating away processes, so more
liquid can grab more solid in the same amount of time. Thus stirring or shaking will help a
_______________ dissolve faster in a liquid.
D) When a gas dissolves in a liquid, it is basically trapped by the liquid molecules. If the liquid is
_______________, it removes the water molecules that are trapping the gas, and the gas will form bubbles
and eventually _______________ the liquid. This is why shaking a carbonated beverage makes so many
bubbles.
Let’s summarize ways to increase solubility and speed up dissolving:
Method
Solid dissolved in liquid
Gas dissolved in liquid
Temperature
Particle Size
Pressure
Agitation
15.2 Solution Concentration
1) Just knowing that a solution is unsaturated does not indicate much about the solution. Is there only a little bit of
solute, or is there a lot and it is almost saturated? The only way to tell is to know the solutions
_______________.
2) In general if there is a lot of solute in the solvent, the solution is called _______________, and if there is only a
little bit of solute in the solvent it is called _______________. But chemists need a more exact way to know
how concentrated or dilute the solution is. Chemists have 5 different ways to determine numbers for
concentration. Each way is different and useful in different situations.
A) Percent by _______________ = mass of solute divided by the mass of solution × 100%
B) Percent by _______________ = volume of solute divided by the volume of solution × 100%
C) Molarity = moles of solute divided by the _______________ of solution
D) Molality = moles of solute divided by the _______________ of solvent
E) Mole _______________ = moles of solute divided by the total moles of solute and solvent
15.3 Colligative Properties of Solutions
1) Physical properties of solutions that are affected by how much solute is dissolved are called _______________
properties. (Colligative means “depending on the collection”.) There are three colligative properties that we’ll
be concerned with: _______________, boiling point _______________, and freezing point _______________.
A) If a solute dissolved in solutions ionizes (breaks apart into positive and negative parts) these parts will
allow electricity to travel through the solution. For example: _______________ water will not conduct
electricity, but if table salt is added, then the sodium and chlorine that break apart will conduct electricity.
NaCl → Na+ + ClSolutions that conduct electricity are called _______________. The more of an ionizing solute that is
dissolved, the better the conduction of electricity will be. On the other hand, solutes that don’t ionize (like
sugar) will not conduct electricity in water. So sugar water will not conduct electricity. Solutions that
don’t conduct electricity are called _______________.
B) Boiling happens when the molecules of a liquid get enough energy to break through the liquid-gas barrier
and escape as a gas. If a solute is added, it gets in the way of the liquid trying to escape, and thus it takes
more energy (more heat) to get the liquid to boil. This is called boiling point _______________.
If pure water boils at 100 °C, and salt is added, the solution will no longer boil at 100 °C, but will
boil at a _______________ temperature. Often the directions for cooking pasta require the addition of salt
to the water. This causes the water to boil at a hotter temperature and thus the pasta cooks quicker (and the
salt adds some flavor to the pasta).
The _______________ solute that is added, the _______________ the boiling point will be. Thus
the boiling point elevation is directly proportional to the _______________ of the solution.
C) Similar to boiling point elevation is freezing point _______________. Now the solute lowers the
temperature at which the solution freezes. Pure water freezes at 0°C, but salt water freezes below that
temperature.
Just like with boiling point elevation, freezing point depression is directly proportional to the
_______________ of the solution. This is why “anti-freeze” is added to car engines and salt is added to icy
roads. This is also why salt is added to the ice when making ice cream - some of the ice melts to make the
rest of the ice colder - cold enough to freeze cream.