Molecular Modeling
Chapter 8
Solution
s
Open the PHET site labeled molarity
http://phet.colorado.edu/en/simulation/molarity
Choose the solute potassium dichromate. Start with the amount
of solute at 0 and the volume of solvent (water in this case) to 1
liter. Notice the molarity is at 0. Add solute to the 0.100
mark. The molarity is 0.10
moles/liter. Decrease the volume to .5 liters and show the
calculation for the resulting molarity. (Recall Molarity
=moles/liters)
Keeping the volume at .5 liters add the solute to .25 moles.
Record the molarity.
Increase the solute to .300 moles, describe the solution and the
molarity.
Increase the solute again and explain the results.
Now add water to the .7 liter mark, note the solution is no
longer saturated. Add solute until it becomes saturated. Notice
the molarity and explain what saturation means.
Switch to at least 2 different solutes and change the solvent and

solutes until you find the saturation molarity. Record them and
use an equation to show the moles and liters at that molarity.
Open the PHET site simulation labeled concentration.
http://phet.colorado.edu/en/simulation/concentration
Select the solute cobalt(II) nitrate. Shake some of the cobalt
(II) nitrate into the water. Place the purple sensor into the
solution and record the concentration and units.
Use an equation to show a prediction as to what will happen to
the molarity when you add water to the 1 Liter mark. Try it.
Were you successful?
Reset and add a different solute keeping the volume at 1L.
Again use an equation to make a prediction as you evaporate the
water down to the first line (.9 liters). Try it. Practice until
you feel you can do Molarity conversations.
Go to the Phet simulation called salts and solubility
http://phet.colorado.edu/en/simulation/soluble-salts
What is the volume of water in the simulation?
Shake some salt into the solution. How many sodium ions are
present in the water?
What do you notice about the ratio of sodium to chlorine?
Explain why.
Notice that there are no bound sodium chloride molecules. The
reason is that the sodium and chloride ions are more attracted to
the water than to each other and table salt is completely
dissociated by the water. Shake the salt a few more times and

calculate the molarity of the solution. For example: I shook
and 10 sodium ions were present, so according to the equation,
NaCl à Na
+
(aq)
+ Cl
-
(aq)
so 10 atoms Na
+
X
1
atom
NaCl
= 10 atoms NaCl X
1 mole
= 1.66 X 10
-23
moles
1 atom Na
+
6.02 X 10
23

atoms
And
1.66 X 10
-23
moles
NaCl = 0.33 M NaCl
5.0 X 10
-23
liters
Repeat this with different amounts of water and salt and show
your molarity calculations.
On the top change to slightly soluble salts. Choose one and
shake 4 or 5 times.
Write the formula for the metal salt.
Draw or describe the difference in this salt verses table salt.
Explain why this occurs.
How many atoms of the metal ion are present?
How many atoms of the metal ion are dissolved?
How would this affect the molarity of ions? Explain.
If you added 1 mole of this salt to water making a 1 Liter
solution, how would it’s molarity of ions compare to 1 mole of
table salt in a 1 liter solution?