| Aim | To study the shift in equilibrium between [Co(H2O)6]2+ and chloride ions by changing the concentration of either of the ions and to determine the equilibrium constant for the reaction. |
| Apparatus Required | 0.1 M cobalt chloride solution 0.1 M hydrochloric acid solution 0.1 M silver nitrate solution Distilled water Dropper Test tubes Burette Glass rod Stirrer White tile Stopwatch Thermometer |
| Theory | In this experiment, the equilibrium reaction studied is the one between [Co(H2O)6]2+ and chloride ions. The equation for the reaction is: [Co(H2O)6]2+ + 4Cl- ⇌ [CoCl4]2- + 6H2O The equilibrium constant for the reaction can be calculated using the following equation: Kc = [CoCl4]2- / [Co(H2O)6]2+ [Cl-]^4 The shift in equilibrium can be observed by changing the concentration of either the cobalt or chloride ions. |
| Procedure | Prepare a 0.1 M cobalt chloride solution and a 0.1 M hydrochloric acid solution. Mix 5 mL of the cobalt chloride solution and 5 mL of the hydrochloric acid solution in a test tube. Add 5 mL of distilled water to the test tube and stir the solution. Add 1 mL of the silver nitrate solution to the test tube to remove any chloride ions that are not part of the equilibrium reaction. Filter the solution and discard the precipitate. Transfer the filtrate to another test tube. Add 1 mL of the silver nitrate solution to the test tube to ensure that all chloride ions have been removed. Use a dropper to add 1 mL of the 0.1 M hydrochloric acid solution to the test tube and stir the solution. Use a burette to add 0.1 M hydrochloric acid solution dropwise to the test tube, stirring the solution after each addition. After each addition, use a glass rod to transfer a drop of the solution to a white tile. Add a drop of 0.1 M silver nitrate solution to the drop on the white tile to test for the presence of chloride ions. Continue adding hydrochloric acid solution until the white precipitate formed by the silver nitrate solution disappears, indicating the removal of all chloride ions. Record the volume of hydrochloric acid solution added. Repeat steps 8 to 13, but this time use a dropper to add 1 mL of the 0.1 M cobalt chloride solution instead of the hydrochloric acid solution. Calculate the equilibrium constant (Kc) for the reaction using the volumes of hydrochloric acid solution added in each trial and the concentrations of the solutions used. |
| Observation and Results | When hydrochloric acid solution was added to the solution of [Co(H2O)6]2+ and chloride ions, the white precipitate formed by the silver nitrate solution disappeared gradually as more acid was added. When cobalt chloride solution was added instead of hydrochloric acid solution, the white precipitate formed by the silver nitrate solution disappeared more quickly than in the previous trial. The volume of hydrochloric acid solution required to remove all chloride ions was greater |