please help!!! Dion (Fe reacts with thiocyanate ion iscN to form a md eom plex i

Question

please help!!!

Dion (Fe reacts with thiocyanate ion iscN to form a md eom plex ion with the iormula lFescNI' The net equation describirs this reaction is even in Equatian 10 A student studying this uilibrium besine with an equilibrium mixture that is ighi pink. an what charge will the student observe when solution ontaining Fe' ion added to this Briefly explain how your answer to is consistent with Le Chaneliers prinople Selver kon CAg reacts with soN ian to form silver thicxyanaue AssCN What change will the student observe when a solution antatning Ag ion is added to the misture' Briefly explain how your answer is ocesi ant with teler's principle

Explanation / Answer

The net ionic equation for the reaction is

Fe3+ (aq, yellow) + SCN- (aq, colorless) <=====> [FeSCN]2+ (aq, red)

The equilibrium constant for the reaction is

Keq = [Fe(SCN)2+]/[Fe3+][SCN-]

(1) When a solution containing Fe3+ is added to the solution, the faint pink color of [FeSCN]2+ turns to deep red.

(2) As per Le-Chatilier principle, when a stress is added to a system at equilibrium, the system will adjust in such a way as to nullify the effect of the stress. It is important to remember that at a particular temperature, Keq remains constant.

When Fe3+ is added to the system at equilibrium, [Fe3+] increases. To counter-balance the enhanced concentration of Fe3+, more [FeSCN]2+ must be formed (so that Keq remains constant). Therefore, the pink color of the solution intensifies to dark red.

(3) The reaction taking place between Ag+ and SCN- is

Ag+ (aq, colorless) + SCN- (aq, colorless) ------> [AgSCN] (s, colorless)

When a solution containing Ag+ is added, the pink color of [FeSCN]2+ gradually disappears and the solution turns pale yellow.

(4) The reason for the color change can again be explained with Le Chatilier principle. Ag+ complexes with SCN- and removed SCN- from the system. The denominator in the expression for Keq therefore decreases. To keep Keq constant, the numerator must decrease proportionately. This is possible only when [FeSCN]2+ breaks down to furnish more SCN-. Therefore, the reverse reaction is favored producing more Fe3+ and SCN-. Since Fe3+ is yellow in color, the pink color of the [FeSCN]2+ solution will gradually turn to yellow due to the increased Fe3+.

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