Video 2: Chemical Equilibrium: Colorful Demonstrations , Tommy Technetium YouTube Channel (accessed ) Indeed, I have noted that solutions of CuCl 2 in acetone are dirty-yellow at room temperature, green when incubated in a dry-ice acetone mixture, and orange-yellow when incubated in hot water (Video 2). Because of this, each reaction shifts to the right at increasing temperatures, but to the left at decreasing temperatures. Note that each reaction listed in Scheme I is endothermic from left to right. Each reaction is endothermic from left to right. Scheme I: Putative compounds, reactions, and colors involved in the formation of various copper-chloro complexes in acetone. 4 This system of Cu 2+ complexes has the added benefit of displaying a larger variety of colors: blue, green, yellow, and orange (Scheme I). 1-3 Because concentrated HCl presents several hazards, I have instead begun using a system of Cu 2+ complexes, which does not require the use of concentrated acid, to explore chemical equilibrium. In this demonstration, concentrated HCl (12 M) is used as the source of Cl - to produce the blue colored CoCl 4 2- species. Video 1: Cobalt equilibrium and thermodynamics, Tommy Technetium YouTube Channel (accessed ) Therefore, the above reaction can be shifted to the right at high temperatures or to the left at low temperatures (Video 1). The reaction that forms CoCl 4 2- is endothermic. When Co 2+ is dissolved in water it appears pink, but it forms a blue-colored complex in the presence of high concentrations of chloride ion: 1-3Ĭo 2+(aq) + 4 Cl -(aq) ←→ CoCl 4 2-(aq) Equation 1 Chemical Demonstrations: A Handbook for Teachers ofĬhemistry Wisconsin 1983 Vol.A popular method for demonstrating the effect of temperature on chemical equilibrium involves the use of Co 2+ complexes. Ealy Chemical Demonstrations: A Sourcebook for Teachers. Use caution working with acidic solutions. Add water, however, and the equilibrium will shift back towards the pink hydrated species. If the chloride or cobalt concentrations increase, the equilibrium will also shift towards the blue anhydrous cobalt chloride. Cooling will shift the products towards the hydrated complex, which is more pink. If heat is added, the equilibrium will shift towards the cobalt chloride complex, which is blue in color. 2+(aq) + 4 Cl- 2-(aq) + 6H 2OĪ change in temperature or concentration of the ions will shift the equilibrium. Observe the colors of the solutions after several minutes.Īlternatively you can use the heat gun to increase the temperature of the cobalt chloride solutions to shift the equilibrium.Īn equilibrium exists between a hydrated cobalt species and anhydrous cobalt chloride, both have an oxidation state of 2+.

Place one of each tube in the ice bath.Ĥ. Place one of each tube in the hot water.ģ. Hot plate is located in the top drawer opposite the chemical storage cabinets or on the center bench. ‡Test tubes with pre-prepared solutions and beakers are located in the solutions cabinet. ice water bath (get ice from Gen chem labs prior to class).2 Pre-prepared test tubes with aqueous cobalt chloride (purple solutions)‡ in beaker.2 Pre-prepared test tubes with cobalt chloride and HCl (pink solutions)‡ in beaker.The tube placed in cold water will turn more pink. The tube placed in hot water will turn blue. Description: Test tubes containing a pink solution of cobalt and chloride ions are placed in hot water and cold water.

Cobalt chloride le chatelier lab