Le Chatelier's Equilibrium Lab

20 points

Purpose:  To illustrate the properties of Le Chatelier's Principles of Equilibrium

 

Pre-Lab Questions:  (4 points)

                  1.  If a reaction is endothermic, what should you do to the reaction to

             shift the equilibrium to favor the products?  a.  Heat it     b.  Cool it

            2.  If a reaction is exothermic, what should you do to the reaction to shift the equilibrium to

            favor the products?  a.  Heat it.  b.  Cool it.

            3.  Several ways to favor the products of a reaction is to (select the TWO correct

            answers):  a.  add more reactants   b.  add more products  c.  remove reactants   

d.  remove products.

            4.  Name at least two visual indications you can see during a reaction to see if a reaction is

            shifting to favor either the products or the reactants.

            5.  Name at least four things you can do to affect the rate at which a reaction occurs.

            6.  How would you write the Keq for the following reaction: 

                                    Fe3+­(aq) + SCN- (aq) <----> FeSCN2+ (aq)  (FeSCN2+  Is a Dark Red Color.)

            7.  How would you write the Keq for the following reaction:

                                    Co(H2O)62+ (aq)  +  4Cl- (aq)  + energy  <------>  CoCl42- (aq)  + 6H2O(l)

            8.  Is the reaction in pre-lab question #7 endo or exothermic?

9.  If the Keq value for the equation in #7 is 1.75 L4/mole4, does that mean

the equilibrium of this reaction favors the products or favors the reactants?

 

Materials:

            Plastic Well Plate

            White Sheet of Paper

            MicroPipette  USE THE MICROPIPETTE IN PROCEDURE PART II ONLY!!!!!!!!!!!!

 

Procedure Part I:

            1.  In four empty wells of the well plate, place enough FeCl3 and KSCN to fill the wells

            to about 1/2 full.  Use an equal amount of drops of FeCl3 as you do KSCN.

            2.  To each of these four wells, add 5-6 drops of the following chemicals:  (add only one

            type of each chemical to each well).  IMPORTANT:  REMEMBER WHICH WELL GOT

            WHICH CHEMICAL ADDED TO IT!!!!!!!!!!!!!!!

                        Iron (II) nitrate

                        Potassium Bromide

                        Sodium Carbonate

                        Sodium Hydroxide

           

            3.  Record the color change after the addition of each one of these chemicals in your data

            table.  The choices you will have for color change are:  "Turns yellowish/clear",  "Turns More Red", 

            "No Change"

            4.  Rinse all of this down the sink and dry out your well plates.

 

Data Table:  (2 point)

 

Chemical added                                  Color Change            

Iron (II) nitrate                          _______________

Potassium Bromide                   _______________

Sodium Carbonate                    _______________

Sodium Hydroxide                    _______________


Questions:  (6 points)

            1.  Which one(s) of these chemicals that you added made the reaction shift more to the

            right?

            2.  Why did this/these chemicals shift the reaction to the right?

            3.  What visual clue did you have that the reaction was shifting to the right?

            4.  Look at page 900 (or p. 427 Table 14-1) and explain why the other chemicals did

            what they did to this reaction:  (these are the chemicals which either caused "No Change" or

            "Turns yellowish/clear".)  Show your answers as you see them written below - use a full sentence.

            Name of Chemical:                              Why did it have this effect?

            ______________________                            ___________________________________

            ______________________                ____________________________________

            ______________________                ____________________________________

 

Procedure Part II:

            1.  Make an ice water bath in a 150 mL beaker. 

            2.  Make a hot water bath in a 150 mL beaker on a hot plate.

            3.  Fill one well plate well 1/2 way full with CaCl2 pellets.

            4.  Add enough Cobalt (II) chloride to the same well to fill it almost to the tippy top.

            5.  Use your plastic pipette to stir the solution until all of the CaCl2 pellets are dissolved in the solution. 

            6.  If your solution is now purple, you can go on to step #7.  If it is still pink, please add some more CaCl2

until the solution is purple.

            7.  Draw up the entire contents of the well into the micropipette BULB.  This means that the entire contents of

the well plate should be in the BULB of the pipette, not the stem.

            8.  Submerge the bulb of the micropipette alternately into the hot water and the cold water.  Record the color

change you get in the hot water vs. the color change you get in the cold water on your data table.

 

Data Table:  (2 point)

            Color of solution in Hot Water:   ______________________

            Color of solution in Cold Water:  ______________________

 

Questions:  (6 points)

 

     1.  Use the information provided in the pre-lab to determine which color is associated with which chemical.

            Chemical                     Color

            Co(H2O)6 2+(aq)                ___________

            CoCl4 2-(aq)                    ___________

 

     2.  COPY THE FOLLOWING SENTENCE EXACTLY AS YOU SEE IT HERE ONTO YOUR LAB WRITE UP.  SIMPLY CHOOSE THE CORRECT WORDS WHERE UNDERLINED AND BOLDED:  “The Keq of this reaction is 1.75 L4/mole4 at room temperature.  This means that the reaction favors the PRODUCTS/REACTANTS at room temperature.  Since the color of the solution at room temperature was PURPLE/PINK, we know that Co(H2O)6 2+(aq)/ CoCl4 2-(aq) was the chemical of that color because that chemical is on the PRODUCTS/REACTANTS side.”

 

     3.  Use the sentence format you see in question #2 to answer this:  How did the placement of the word “energy” in the original balanced equation help you determine which chemical belonged with which particular color as you performed the experiment?  (example answer:  “Because “energy” is on the…………………..etc”).