D. Complex Ion Equilibrium Cocl and Cot 2- io Coc 6 H4CT Co(H,heat The effect on
ID: 1015223 • Letter: D
Question
D. Complex Ion Equilibrium Cocl and Cot 2- io Coc 6 H4CT Co(H,heat The effect on equilibrium can be observed due to color changes: the Coclion (the "chloro" complex) is purple-blue and the Co(H 0) (the "aqua" complex) ion is pink. The conversion from one form to the other involves an energy change, and therefore the equilibrium is temperature dependent 1. Add 5 mL of 0.1 M CoCl2 (in methanol) into a test tube. Add (dropwise) a minimal amount of DI water to the blue CoCl2 complex to change the color to that of the pink aqua complex. DO NOT ADD Too MUCH WATER Divide the pink solution equally into three test tubes. 2. 3. 4. To test tube #1, add 12 M HCl dropwise until a color change is observed. 5. Place test tube #2 in a hot ater bath (65 to 70°C) Record any observations, 6. Place test tube #3 in an ice bath. Record any observations, and answer data 7. Dispose of the waste in the appropriate waste container. Mix, record any observations, and answer data questions Q D.1-QD.3 and answer data question Q.D.4 questions Q.D.5 and Q D.6.Explanation / Answer
D.4. Observation: the colour will change back to blue.
Q.D.1. The pink colour complex is called aqua complex because the Co2+ makes complex with H2O molecules. Water is also called aqua, so the complex is called aqua complex.
Q.D.2. In step D.4, the HCl is added to the system. By addition of HCl, Cl- ions increase in the system. According to Le-chatelier principle, the reaction will start moving in the backward direction, because the ions of Cl- has increased. The aqua complex will again react with Cl- ions to give CoCl2 and colour will change back to blue.
Q.D.3. The CoCl2 solution is made in methanol and not water because the as soon as we add water to the sample, it starts forming aqua complex.
D.5. Observation: the colour will change back to blue.
Q.D.4. The reaction is exothermic. So, on increase of temperature, the reaction will shift in backward direction. According to Le-chatelier principle, the reaction moves in the direction to oppose the effect. As the reaction is exothermic, so it is releasing heat. On further increasing temperature, it will try to negate the effect and thus, it will move in the direction in which heat is absorbed.
D.6. Observation: the colour will change back to blue.
Q.D.5. The reaction is exothermic. By putting it in ice, we are decreasing the temperature of the system. Exothermic reactions move in forward direction because heat is being released and according to Le-chatelier principle, the reaction moves in the direction to oppose the effect. On decreasing temperature, it will try to negate the effect and thus, it will move in the direction in which heat is released.
Q.D.5. The reaction is exothermic. In the reaction, it is written + heat on products side. So, heat is released and thus it is exothermic.
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