 We will now look at the equilibrium between a cobalt water complex ion, which is pink, and a cobalt chloride complex ion, which is blue. We'll start with two test tubes with the cobalt water complex ion. We add 12 molar hydrochloric acid to one of the tubes. We notice that the solution turns blue. This indicates that the equilibrium has shifted in the reverse direction. The hydrochloric acid provides a source of chloride ion. As we increase the concentration of the product, the equilibrium shifts in the reverse direction to use up the added chloride ion. We will now add water to the test tube. We notice that the solution has turned back to pink. By adding water to the solution, we've shifted the equilibrium back in the forward direction. We'll start with two test tubes with the cobalt water complex ion. We add 12 molar hydrochloric acid to one of the tubes. We notice that the solution turns blue. This indicates that the equilibrium has shifted in the reverse direction. The hydrochloric acid provides a source of chloride ion. As we increase the concentration of the product, the equilibrium shifts in the reverse direction to use up the added chloride ion. We will now add some silver nitrate solution to the cobalt chloride complex ion. We notice the formation of a white solid, which is the silver chloride. We also notice that the solution has turned from blue to pink. The silver ion removes chloride ion from solution as solid silver chloride. The equilibrium shifts in the forward direction to try and replace the chloride ion that's been removed. We're going to take a test tube containing the equilibrium mixture. The solution is pink, indicating that we have a high concentration of the cobalt water complex ion. We're going to put this into a warm water bath. As we warm the solution, the solution turns from being pink to blue. If you heat an equilibrium mixture, the equilibrium will shift in the endothermic direction. This is an indication that this reaction is endothermic in the reverse direction. Cooling the reaction mixture shifts the equilibrium in the exothermic direction. We notice that as we cool this, the solution goes from being blue to pink, indicating that the reaction is exothermic in the forward direction.