Dynamic Equilibrium and Le Chatelier’s Principle
Experiment No. 2: Dynamic Equilibrium and Le Chatelier’s Principle December 1, 2011
Final Formal Results
Le Chatelier’s Principle states that “when a stress is applied to a chemical system at equilibrium, the equilibrium shifts in a direction that reduces the effect of stress” (Gross, Abenojar, and Tan 23). Moreover, it helps us “predict the direction of the shift of the equilibrium” (Silberberg 745). Silberberg also stated that there are three kinds of disturbances - concentration, pressure, and temperature - that can be applied to a system at equilibrium. However, only concentration and temperature were observed in this experiment.
Part 1: Cobalt Complexes Table 1 shows the color change of the cobalt chloride solutions as water, different concentrations of hydrochloric acid, and sodium chloride were added as well as the number of drops that caused the color change.
Color of cobalt chloride in ethanol: Violet Color of cobalt chloride in water: Red
Medicine Dropper Calibration: 1 mL = 16 drops Table 1. Cobalt Complexes
Solution Color Change # of drops mL
CoCl2 in EtOH + H2O red-violet 5 0.31 + 12 M HCl blue 9 0.56
CoCl2 in H2O + 0.5 M NaCl light red 18 1.12 + 0.5 M HCl light red 20 1.25 + 1 M HCl light red 20 1.25 + 6 M HCl reddish pink 25 1.56 + 12 M HCl reddish pink 23 1.44 The equilibrium equation for this reaction is
Co(H2O)62+ + 4 Cl- CoCl42- + 6 H2O [4] pink blue
Addition of water caused the concentration of the products to increase, thus shifted the equilibrium to the left. The reaction then produced more Co(H2O)62+ to reduce the effect of the stress applied. This, thus, explains why the solution changed into a red-violet color. More drops of water would probably result to a pink color of the solution. On the other hand, when hydrochloric acid was added, the solution turned blue. This was because the equilibrium shifted to the right since Cl- ions were added causing the
Final Formal Results
Le Chatelier’s Principle states that “when a stress is applied to a chemical system at equilibrium, the equilibrium shifts in a direction that reduces the effect of stress” (Gross, Abenojar, and Tan 23). Moreover, it helps us “predict the direction of the shift of the equilibrium” (Silberberg 745). Silberberg also stated that there are three kinds of disturbances - concentration, pressure, and temperature - that can be applied to a system at equilibrium. However, only concentration and temperature were observed in this experiment.
Part 1: Cobalt Complexes Table 1 shows the color change of the cobalt chloride solutions as water, different concentrations of hydrochloric acid, and sodium chloride were added as well as the number of drops that caused the color change.
Color of cobalt chloride in ethanol: Violet Color of cobalt chloride in water: Red
Medicine Dropper Calibration: 1 mL = 16 drops Table 1. Cobalt Complexes
Solution Color Change # of drops mL
CoCl2 in EtOH + H2O red-violet 5 0.31 + 12 M HCl blue 9 0.56
CoCl2 in H2O + 0.5 M NaCl light red 18 1.12 + 0.5 M HCl light red 20 1.25 + 1 M HCl light red 20 1.25 + 6 M HCl reddish pink 25 1.56 + 12 M HCl reddish pink 23 1.44 The equilibrium equation for this reaction is
Co(H2O)62+ + 4 Cl- CoCl42- + 6 H2O [4] pink blue
Addition of water caused the concentration of the products to increase, thus shifted the equilibrium to the left. The reaction then produced more Co(H2O)62+ to reduce the effect of the stress applied. This, thus, explains why the solution changed into a red-violet color. More drops of water would probably result to a pink color of the solution. On the other hand, when hydrochloric acid was added, the solution turned blue. This was because the equilibrium shifted to the right since Cl- ions were added causing the
References: 1. Clark, Jim. Complex Metal Ions - Ligand Exchange Reactions. 2003. 30 November 2011 < http://www.chemguide.co.uk/inorganic/complexions/ligandexch.html>. 2. Clark, Jim. An Introduction to Complex Metal Ions. 2003. 30 November 2011 < http://www.chemguide.co.uk/inorganic/complexions/whatis.html>. 3. Dice, David. The Chromate-Dichromate Equilibrium. 2008. 30 November 2011 . 4. Gross, Richard B., Abenojar, Eric C., Tan, Jake A. Modern Experiments in General Chemistry II. AdMU, Quezon City Philippines: Ateneo de Manila University, 2010. 5. Ladon, L. Chemical Equilibria. 2001. 30 November 2011 . 6. Silberberg, Martin S. Chemistry: The Molecular Natue of Matter and Change. New York: McGraw-Hill, 2006.