CuCl42-
(aq)Copper (II) ions react with halide ions (Cl-, Br-, I-) to form complex ions. While Cu2+ (aq) ions are blue, the resulting product is green. The following equation can be used to represent this process.
Cu2+ (aq) + 4Cl- (aq)
CuCl42-
(aq)
This reaction has an obvious color shift when the temperature is changed. If we assume the reaction is either exothermic, or endothermic, we can use le Châtelier's principle to predict what should happen as the solution changes temperature.
Caution:
Copper(II) chloride is moderately dangerous (harmful if swallowed, causes irritation to skin, eyes and respiratory tract), so be careful not to ingest it, spill on your skin, or get it into your eyes. If it does come in contact with your skin, wash thoroughly with a lot of water. Observe the normal safety precautions you would for a lab where substances are being heated. Wear a lab apron and safety goggles at all times.To investigate the effect of temperature, you will have to design an experiment that can show the effect of temperature on the copper (II) chloride equilibrium as the temperature changes. Here is what you can have for materials: two 18 x 150 mm test tubes, 10 mL of 0.5 M CuCl2 solution, ice cubes, hot water, a bunsen burner and lighter, two 250 mL beakers, thermometer, ring stand and gauze. You can have nothing else.
Create and write down an experimental procedure that will allow you to answer the
following question: is the reaction Cu2+ (aq) + 4Cl- (aq) CuCl42- (aq)
exothermic, or endothermic? Check with your teacher that your procedure is safe before
beginning your investigation. You should be able to conduct your experiment in 15
minutes or less.
Make sure that you can use le Châtelier's principle to properly predict the effect of temperature on a reaction at equilibrium. In your analysis of the results, show how you can predict the reaction shift for a reaction if it is exothermic, or endothermic, and compare the prediction to the real result.