Lab: LeChatelierís Principle
A Study of Chemical Equilibrium
Part I. The Cobalt Equilibrium: Co(H2O)6+2 + 4Cl-1 + heat
(pink)
1.
--> CoCl4-2 + 6H2O
(blue)
Add 1mL (30 drops) of 0.1M cobalt(II) chloride in alcohol to two different test tubes using the
labeled dropper bottle.
A.
#1.
Disturb the equilibrium by adding 4 drops of water, one drop at a time, to test tube
Describe what happens after each drop is added.
B.
Use LeChatelierís Principle to explain what happened. Your explanation MUST mention
reaction rates. Start by showing what happened to the equilibrium using up and down arrows.
Co(H2O)6+2 + 4Cl-1 + heat
(pink)
___
--> CoCl4-2 + 6H2O
(blue)
___
___
___
___
C.
Now disturb the equilibrium in test tube #1 by adding 4 pellets of solid anhydrous
CaCl2.
The anhydrous CaCl2 removes water from the system. Describe what happens around
the pellets.
D.
Use LeChatelierís Principle to explain what happened. Your explanation MUST mention
reaction rates. Start by showing what happened to the equilibrium using up and down arrows.
Co(H2O)6+2 + 4Cl-1 + heat
(pink)
___
--> CoCl4-2 + 6H2O
(blue)
___
___
___
___
E.
Add 1 drop of water to test tube #2, mix and note the color, then place it into the ice water bath at
your lab station and leave it there for 2 minutes. Describe the change.
F.
Use LeChatelierís Principle to explain what happened. Your explanation MUST mention reaction
rates. Start by showing what happened to the equilibrium using up and down arrows.
Co(H2O)6+2 + 4Cl-1 + heat
(pink)
___
G.
--> CoCl4-2 + 6H2O
(blue)
___
___
___
___
Now move test tube #2 from the ice water bath to the hot water bath. Use LeChatelierís Principle
to predict/explain what happens. Your explanation MUST mention reaction rates. Start by
showing what happens to the equilibrium using up and down arrows.
Co(H2O)6+2 + 4Cl-1 + heat
(pink)
___
--> CoCl4-2 + 6H2O
(blue)
___
___
___
___
Part II. The Iron Equilibrium:
Fe+3 + SCN-1 + heat -->
FeSCN+2
(colorless)
(blood red)
2.
A.
Add 1mL (30 drops) of dilute FeSCN+2 solution to four test tubes using the dropper bottle or an
eyedropper. Set test tube #1 aside to use as a color reference/comparison.
Disturb the equilibrium by adding 2 drops of Fe(NO3)3 (a source of Fe+3 ions) to test tube
#2.
Describe the change.
B.
Use LeChatelierís Principle to explain what happened. Your explanation MUST mention
reaction rates. Start by showing what happened to the equilibrium using up and down arrows.
Fe+3 + SCN-1 + heat
(colorless)
___
___
-->
___
FeSCN+2
(blood red)
___
C.
Add some crystals of solid KSCN (a source of SCN-1 ions) to test tube #3. Describe the
change.
D.
Use LeChatelierís Principle to explain what happened. Your explanation MUST mention
reaction rates. Start by showing what happened to the equilibrium using up and down arrows.
Fe+3 + SCN-1 + heat
(colorless)
___
___
-->
___
FeSCN+2
(blood red)
___
E.
Add 5 drops of sodium oxalate (a source of oxalate ions that remove Fe+3) to test tube #4.
Describe the change.
F.
Use LeChatelierís Principle to explain what happened. Your explanation MUST mention
reaction rates. Start by showing what happened to the equilibrium using up and down arrows.
Fe+3 + SCN-1 + heat -->
(colorless)
___
___
___
FeSCN+2
(blood red)
___
Part III. The Copper Equilibrium:
In this exercise your task is to determine which of the chemical equations shown below is the correct one
for this equilibrium:
(I)
CuCl4-2(blue) + 6H2O + Heat
(II)
CuCl4-2(blue) + 6H2O
(III) CuCl4-2(green) + 6H2O + Heat
-->
-->
-->
Cu(H2O)6+2 (green) + 4Cl-1
Cu(H2O)6+2 (green) + 4Cl-1 + Heat
Cu(H2O)6+2 (blue) + 4Cl-1
(IV)
CuCl4-2(green) + 6H2O
3.
Add 1mL (30drops) of CuCl4-2/Cu(H2O)6+2 to 4 test tubes using the graduated eyedroppers. Set
test tube #1 aside as a color reference/comparison.
-->
Cu(H2O)6+2 (blue) + 4Cl-1 + Heat
A.
Add 20 drops of water to test tube #2 and mix. Describe the change.
B.
Which equation(s) can be eliminated from consideration on the basis of this result? Explain.
C.
Add 1mL (30 drops) of saturated NaCl (a source of Cl-1 ions) to test tube #3. Describe the
change.
D.
Is this consistent with your results from part B of this section? Explain.
E.
Why did the NaCl have to be dissolved in ethanol for this lab instead of water?
F.
Place test tube #4 into the hot water bath for 2 minutes. Describe the change.
G.
Which equation(s) can be eliminated from consideration on the basis of this result? Explain.
H.
Write the correct equation for the copper equilibrium in the space below: