Part IV - Equilibrium of Cobalt complexes Do this step and step 2 in the hood .

Question

Part IV - Equilibrium of Cobalt complexes

Do this step and step 2 in the hood. Obtain a test tube with some of the pink Co(H2O)62+ solution. These have been pre-filled for you. Add 12M HCl (USE CAUTION!! WEAR GOGGLES!!) dropwise until a color change is observed. Record your observations.

Observation for 1a. It turned to blue, and then 2a. it turned back to pink. at 3a. the color changed to blue when we heated it, and at 33 the color changed back to pink when we cooled it.

Part IV 1a. What is happening at the molecular/ionic level as HCl is added? How does the equilibrium respond to the addition of HCl?

Part IV 1b. What is the role of the H+ ions? Of the Cl- ions?

  Add distilled water dropwise until a color change is observed. Record your observations. Save this test tube for step 3.

Part IV 2a. How does the equilibrium react when water is added? Is the water just diluting the solution or is it reacting chemically with the solute? How do you know? What is the evidence?

Use a hot plate to heat a 150 mL beaker of water to boiling. Using the test tube of solution from step 2, gently heat the test tube by submerging it in the boiling water. Observe and record any color changes. Cool the solution in a beaker of tap water and observe any color changes.

Part IV 3a. What happens to the position of the equilibrium as heat is added to, or removed from the system?

Part IV 3b. Does suggest that the reaction is endothermic or exothermic? Explain.

Explanation / Answer

Part IV 1a. As soon as HCl is added to solution, HCl dissociates as H+ and Cl- being a strong acid. The Cl- reacts with the Co complex. By adding HCl to Co(H2O)62+ , the following reaction happens.

Co(H2O)62+ + 4Cl- ---------> CoCl42- + 6H2O

By addition if HCl, the reaction moves in the forward direction.

Part IV 1b. H+ ions will decrease the pH of the solution. The Cl- ions will react with the complex to give CoCl42-.

Part IV 2a. By addition of water, the equilibrium will shift in backward direction. According to Le-chatelier principle. the addition of products, will shift the reaction towards left. The complex Co(H2O)62+ will start forming. Water molecules are reacting with CoCl42-, the Cl- ion will be replaced by H2O molecules. The evidence for this reaction is the colour of the solution will again change to pink from blue.

Part IV 3a. When the heat is added to the system, the color of the solution will become blue and when the heat is removed, the color of the solution will change into pink.

Part IV 3b. The reaction is endothermic, means we need to give heat for the reaction to move forward. The addition of heat is pushing the reaction in forward direction. According to Le-Chatelier principle, the reaction always tries to move in the direction to counteract the change.

Related Questions

Navigate

• Browse (All)
• Browse P
• Subjects