Cobalt ions form complex ions with water and chloride as shown in the reaction. The left side of the reaction is pink, and the right side of the reaction is blue.

Co(H₂O) ₆ ² ⁺ + 4CI ⁻ + heat ⇌ CoCI ₄ ² ⁻ + 6H ₂O

Which statement about the system at equilibrium is correct?
1. Cooling a purple solution will turn it pink
2. Heating a blue solution will turn it purple
3. Adding water to a purple solution will turn it blue
4. Adding hydrogen chloride (HCI) to a blue solution will turn it purple

Would it be #2? Wouldn’t heating the blue solution cause it to go towards pink and make it purple?

Wait it would be 1, the purple would turn pink when cooled down

To determine the correct statement about the system at equilibrium, let's analyze the given reaction and understand the color changes that occur.

In the forward reaction:
Co(H₂O)₆²⁺ + 4CI⁻ + heat ⇌ CoCI₄²⁻ + 6H₂O

The reactants on the left side of the reaction include a pink complex ion, Co(H₂O)₆²⁺, and chloride ions (CI⁻). The heat added indicates that this reaction is endothermic, meaning it absorbs heat energy from the surroundings.

On the right side of the reaction, a blue complex ion, CoCI₄²⁻, and water molecules (H₂O) are formed.

Knowing this, let's evaluate the given statements:

1. Cooling a purple solution will turn it pink: Since the forward reaction is endothermic, cooling the system would favor the reactants' formation, including the pink complex ion. Hence, cooling a purple solution will indeed turn it pink. This statement is correct.

2. Heating a blue solution will turn it purple: Since the forward reaction is endothermic, heating the system would favor the products' formation, including the blue complex ion. Thus, heating a blue solution would not turn it purple, but rather it would maintain its blue color. This statement is incorrect.

3. Adding water to a purple solution will turn it blue: From the reaction, adding water to the left side (reactants) would shift the equilibrium towards the right side (products). Since the products include a blue complex ion, adding water to a purple solution would indeed turn it blue. This statement is correct.

4. Adding hydrogen chloride (HCl) to a blue solution will turn it purple: Adding hydrogen chloride to the blue solution would shift the equilibrium of the reaction towards the left side (reactants). Since the reactants include the pink complex ion, adding hydrogen chloride to a blue solution would turn it pink, not purple. This statement is incorrect.

In conclusion, statements 1 and 3 are correct, while statements 2 and 4 are incorrect.

Remember Le Chatelier's Principle. If we do something to a chemical system at equilibrium the system will try to undo what we did. Lets look at them 1 by 1.

4. Adding HCl will shift the equilibrium to the right (to get rid of the Cl^- that has been added). So statement 5 is not right.
3. Adding water will shift the equilibrium to the left (to get rid of the H2O that was added). So statement 3 is not right.
Analyze statements 1 and 2 the same way. Post your work if you want me to check it.