Question

I recently performed a lab on Chemical Equilibrium.

Here is some background on the experiment:

-We made a stock solution by combining Fe(NO3)3 and NH4SCN. This made a blood red solution. Then, we added different reagents to see the change of color and the shift of equilibrium.

I'm being asked the following question: Based on the color of solutions reported, determine the direction of the reaction's: Fe^3+(aq)+SCN^- --> [FeSCN]^2+(aq) equilibrium shift upon each addition of each reagent investigated and write the chemical reaction involving the reagent that is reponsible for the shift.

We investigated the following additions:

a. 0.1 M silver nitrate

-Upon adding silver nitrate to the stock solution, the color changed from blood red to a cloudy clear color with a black precipitate.

b. 1 M sodium chloride

-Upon adding sodium chloride to the stock solution, the color changed from blood red to a clear, light orange color.

c. 0.5 M sodium hydroxide

-Upon adding sodium hydroxide to the stock solution, the color changed from blood red to a yellow color.

d. 1 M sodium hydrogen phosphate

-Upon adding sodium hydrogen phosphate to the stock solution, the color changed from blood red to a clear color.

Please explain how you determined the shift and wrote the chemical reaction formula..I don't understand how to determine either. Thank you for your help.

Answer 1

Reaction,

Fe3+ + SCN- ---> [Fe(SCN]2+

the reaction is performed under acidic medium

So,

a. When AgNO3 is added

FeSCN2+ complex reacts with added Ag+ and forms Fe3+ and AgSCN species. the red color of original complex disappears.

b. 1 M NaCl is added

Added Na+ displaces Fe from complex and disappearence of solor is seen. Formation of FeCl3 species gives organge coloration.

c. 0.5 M NaOH is added

Reduced H+ concentration on reactant end and thus, more products react to form substrate. Color disappears to original solution color.