1. A student obtained a test tube with asuspension of white, slightly soluble ma
ID: 684175 • Letter: 1
Question
1. A student obtained a test tube with asuspension of white, slightly soluble magnesium hydroxide in water.This system was at equilibrium as represented by the followingequation:Mg(OH)2 (s) <--> Mg2+ (aq) + 2 OH- (aq)
Write the equilibrium constant expression for this reaction.
Kc = [Mg2+][OH-]^2
Chemistry, The Central Science says, “Whenever a pure solidor a pure liquid is involved in a heterogeneous equilibrium, itsconcentration is not included in the equilibrium-constantexpression for the reaction.”
2. According to Le Châtelier’s principle, what willhappen to the equilibrium in question 1 if nitric acid, HNO3, isadded? Hint, will HNO3 react with any of the products or reactants?Explain your answer.
The ions of HNO3 would react with the ions of OH-. The OH- isremoved and the equilibrium is shifted.
3. According to Le Châtelier’s principle, what wouldhappen to the equilibrium in question 1 if soluble magnesiumchloride was added to the solution? Explain your answer.
The addition of MgCl2 adds more Mg and causes a shift inequilibrium.
4. The student heated the solution described in question 1 andfound that more of the Mg(OH)2 dissolved. Is the reactionendothermic or exothermic? Explain your answer.
Heat and Mg(OH)2 are being consumed by the products. The reactionis endothermic. 1. A student obtained a test tube with asuspension of white, slightly soluble magnesium hydroxide in water.This system was at equilibrium as represented by the followingequation:
Mg(OH)2 (s) <--> Mg2+ (aq) + 2 OH- (aq)
Write the equilibrium constant expression for this reaction.
Kc = [Mg2+][OH-]^2
Chemistry, The Central Science says, “Whenever a pure solidor a pure liquid is involved in a heterogeneous equilibrium, itsconcentration is not included in the equilibrium-constantexpression for the reaction.”
2. According to Le Châtelier’s principle, what willhappen to the equilibrium in question 1 if nitric acid, HNO3, isadded? Hint, will HNO3 react with any of the products or reactants?Explain your answer.
The ions of HNO3 would react with the ions of OH-. The OH- isremoved and the equilibrium is shifted.
3. According to Le Châtelier’s principle, what wouldhappen to the equilibrium in question 1 if soluble magnesiumchloride was added to the solution? Explain your answer.
The addition of MgCl2 adds more Mg and causes a shift inequilibrium.
4. The student heated the solution described in question 1 andfound that more of the Mg(OH)2 dissolved. Is the reactionendothermic or exothermic? Explain your answer.
Heat and Mg(OH)2 are being consumed by the products. The reactionis endothermic.
Explanation / Answer
Your answers are in essence correct, however they are not particularly complete. For example, for number two you said: "The ions of HNO3 would react with the ions of OH-. The OH- is removed and the equilibrium is shifted." My question for you would be, which way is the equilibrium shifted? This is necessary for you to include in your answers to display that you understand the shifting in equilibria. So, you would say that the equilibrium will shift to the right because OH- is being removed. For number three you would say due to the additive Mg2+ added, the equilibrium will be shifted to the left. Number 4 is fine. Best of luck.
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