molecular modeling chapter 8 solutions open phet site labeled molarity httpphetcoloradoeduen

Molecular Modeling

Chapter 8 Solutions

Open the PHET site labeled molarity

  1.  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)
  2. Keeping the volume at .5 liters add the solute to .25 moles.  Record the molarity. 
  3. Increase the solute to .300 moles, describe the solution and the molarity. 
  4. Increase the solute again and explain the results.
  5. 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.
  6. 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.

  1.  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.
  2. 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? 
  3. 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

  1.  What is the volume of water in the simulation?
  2. Shake some salt into the solution.  How many sodium ions are present in the water?
  3. What do you notice about the ratio of sodium to chlorine?  Explain why.
  4. 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 1023 atoms

And   1.66  X 10-23 moles  NaCl     =     0.33 M NaCl

5.0    X 10-23 liters                  


  1.  Repeat this with different amounts of water and salt and show your molarity calculations.
  2. On the top change to slightly soluble salts.  Choose one and shake 4 or 5 times. 
  3. Write the formula for the metal salt.
  4. Draw or describe the difference in this salt verses table salt.  Explain why this occurs.
  5.  How many atoms of the metal ion are present?
  6.  How many atoms of the metal ion are dissolved?
  7. How would this affect the molarity of ions?  Explain.
    1. 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?


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