In Part I the reaction you observed was Mg(OH)2 (s) Mg2+ (aq) + 2 OH- (aq). Compare the colors you observed in the experiment and answer these questions:
A. Which way should the equilibrium shift when HCl is added? How do your results support your answer?
Shift to left due to increase in Cl– concentration. This is known as the common ion effect on solubility.
B. Which way should the equilibrium shift when Na2EDTA is added? How do your results support your answer?
C. Is this reaction endothermic or exothermic? How do you know?
You don't provide enough information for me to know what you did and I certainly don't know the results of your experiment.
A. When HCl is added, the equilibrium should shift to the left. This is because HCl is a strong acid that dissociates completely in water, producing Cl- ions. Since Cl- ions are already present in the reaction, the addition of HCl increases their concentration. According to Le Chatelier's principle, when the concentration of a reactant is increased, the equilibrium shifts in the direction that reduces the concentration of that reactant. Therefore, the equilibrium shifts to the left to decrease the concentration of Mg2+ and OH- ions, forming more solid Mg(OH)2.
Your results would support this shift if the color change observed in the experiment indicated the formation of more solid Mg(OH)2. Typically, Mg(OH)2 appears as a white precipitate. If more precipitate forms after adding HCl, it would suggest the shift to the left, demonstrating the common ion effect on solubility.
B. When Na2EDTA is added, the equilibrium should also shift to the left. Na2EDTA is a chelating agent that complexes with metal ions. In this case, it will complex with Mg2+ ions, reducing their concentration in the solution. As a result, the equilibrium shifts to the left to compensate for the loss of Mg2+ ions, forming more solid Mg(OH)2.
To confirm this shift, you can observe if the color change after adding Na2EDTA indicates the formation of more solid Mg(OH)2. If more precipitate is formed, it could suggest the shift to the left due to the reduction in the concentration of Mg2+ ions.
C. To determine if the reaction is endothermic or exothermic, you can observe whether heat is absorbed or released during the reaction. One way to determine this is by measuring the change in temperature.
If the reaction is exothermic, it means it releases heat, resulting in an increase in temperature. On the other hand, if it is endothermic, it absorbs heat, resulting in a decrease in temperature.
You can perform the experiment by conducting the reaction and monitoring the temperature change. If the temperature decreases, it suggests that the reaction is endothermic because it is absorbing heat from the surroundings. If the temperature increases, it suggests that the reaction is exothermic because it is releasing heat to the surroundings.