Cobalt(II) ions(pink) react with chloride ions according to the reaction below to form a blue coloured ion complex.

The equilibrium expression for the reaction above is shown below.

The pink solution containing Cobalt chloride ions is heated and after a short time turns blue as shown on the left. Explain according to the observations if the reactionis exothermic or endothermic.

The reaction is endothermic. As heat is applied reaction shifts to the right. This is obvious as the colour change from pink to dark blue indicates the formation of Cobalt(II) chloride ions.

In simple terms imagine energy(E) appearing on the reactants side of the reaction, as shown above. As heat is applied the energy content is increased and the reaction moves to the right in order to remove it.

Look at the equilibrium expression above and predict which way the reaction will shift if the volume of the reactants and product were increased.

At equilibrium at the same temperature the expression above always equals the equilibrium constant"K". If a volume change occurs, say we double the volume and halve the concentration of each species present, then the equilibrium will shift in the direction of maximum particles in an attempt to increase the concentration. In this case it will favour the reverse reaction.

Look at the 120kb video and see if your prediction is correct. The video shows distilled water added to a blue solution of the above reaction at equilibrium. What does the blue colour indicate? The blue colour indicates a high concentration of cobalt(III) chloride ions.

After looking at the video suggest why the top of the test tube turns pink while the bottom half of the test tube remains dark blue. The top halve of the test tube experiences a volume increase very suddenly while the solution at the bottom is yet to be influenced. With diffusion of solute particles the entire solution should turn pink.

What colour change would you predict of NaCl was added to the solution?
A blue colour change is expected as the reaction drives forward to remove the high concentration of chloride ions present.