Le Chatilier Lab

Example 1:

The following equilibrium was established by combining a cobalt (II) nitrate solution, with a sodium chloride solution. When the equilibrium was established, the solution turned from a pink colour to a dark blue indicateding the presence of the CoCl4- ion.

 

[Co(H2O)6]2+ (aq)
+
4 Cl- (aq)
[CoCl4]2- (aq)
+
6 H2O (l)
 

The above equilibrium was now stressed through the addition of silver nitrate (AgNO3), allowed to establish a new equilibrium, which was a pink solution containing a white precipitate in the bottom of the test tube.

Stress:
  • decrease of Cl- ion concentration
    		•
    Shift (with Observational Support)
  • main equilibrium shifts left - since solution turned pink it tells us that there is more [Co(H2O)6]2+ (aq) and less [CoCl4]2- (aq)
    		•
    Explaination:
  • the silver ion in the silver nitrate solution combined with the chloride ion, in the main equilibrium, to form the insoluble silver chloride precipitate in a secondary equilibrium

    •                Ag+ (aq) + Cl- (aq) AgCl (s)

  • this causes the concentration of the chloride ion to decrease in the main equilibrium

  • the main equilibrium shifts left to produce Cl- (aq) by dissociating the blue complex ion [CoCl4]2- (aq) to form the pink complex ion [Co(H2O)6]2+ (aq)
  • also produced more chloride ion and partially increase the [Cl-]
    •