A. The following questions are from experiment EQUL 392: Introducing Equilibrium
ID: 1042676 • Letter: A
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A. The following questions are from experiment EQUL 392: Introducing Equilibrium 1. Consider the equilibrium reaction: Fe (ag) (Lt yellow)+SCN (aq, colorless) [FeSCNj (aq, Red) A student studying this equilibrium begins with an equilibrium mixture that is light pink a. Write the equilibrium constant expression, K, for the reaction b. If he added a solution containing Fe ions, what COLOR change will he observe? c. Silver () ions (Ag) can be removed as an insoluble siver thiocyante, AgSCN by adding AgNO,(aq). What COLOR change will result when a solution containing Ag(1) ions are added to the equilibrium mixture? d. The equilibrium process is [CoCl.P(aq, Blue)+ 6 HOU)Co(H,OP(aq, pink)+4 Ch (aq) is exothermic. What COLOR change you will observe when the temperature is decreased on the equilibrium?Explanation / Answer
a) Equilibrium constant for the reaction ,Keq=[FeSCN2+]/[Fe3+][SCN-]
b) Fe3+ +SCN- <-->FeSCN2+
If Fe3+ is added then the excess of Fe3+ will shift the equlibrium in the forward direction (to counteract the change in Fe3+ concentration ,according to Le Chatlier's principle) producing more of the product ,thereby intensifying the color of the solution from pink to red.(for more FeSCN2+)
c)Ag+ +SCN- -->AgSCN(s) ,thus SCN- shall decrease in the solution.This will change the equilibrium to increase the SCN- by shifting the equilibrium towards left or reactant side.Hence, reverse rxn is favored, producing more SCN-(Le chatlier's principle)
Thus, red color will decrease as product concentration decreases , solution appears light yellow (Fe3+) (SCN- is colorless so masked)
d)When temperature is decreased for an exothermic reaction ,the reaction becomes more favorablein the forward direction (as forward reaction releases energy) .Higher temperature favors reverse reaction.
More of product is formed when temperature is decreased so color changes to pink (product color ) from blue
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