Question

Chemical Equilibrium: Le Chatelier’s Principle.

1. Add 0.5 mL of 0.1 M FeCl3(aq) to 0.5 mL of 0.1 M KSCN(aq), and then add 15 mL of distilled water. To a 2-mL portion of this mixture, add 1 mL of 0.1 M KSCN(aq). Observe any difference in the color from the original solution and explain your observations. Because you are combining equal volumes of equal concentrations, and because they combine in a 1 to 6 mole ratio, Fe3+(aq) should be in excess. After you establish the initial equilibrium, and after dilution with 15 mL of water, when you add more KSCN(aq) you should see the results of a shift in the equilibrium. If you see no change, something went wrong and you should try again.

**Describe the change you observed when you added 1 mL of 0.1 M KSCN to the 2 mL portion of the diluted solution. Copy the equation from the procedure and explain your observations in terms of LeChatelier’s Principle. --

Fe3+(aq) +6SCN-(aq) <--> Fe(SCN)6 3-(aq) It went from a lighter shade of red to a complete maroon color. ??

2. Determine how much distilled water must be added to 0.5 mL of 0.1 M FeCl3(aq) in order to make it 0.001 M. Then carry out the dilution.

**Show your calculations to determine the final volume of the 0.001 M FeCl3 solution. --??

3. Add 0.5 mL of this 0.001 M FeCl3(aq) to 0.5 mL of 0.1 M KSCN(aq), and then add 15 mL of distilled water. To a 2 mL portion of this mixture, add 1 mL of 0.1 M FeCl3(aq). Observe any change in color and explain your observations. In this case, SCN-(aq) should be in excess. After you establish the initial equilibrium, and after dilution with 15 mL of water, when you add more FeCl3(aq) you should see the results of a shift in the equilibrium. If you see no change, something went wrong and you should try again.

**Describe the change you observed when you added 1 mL of 0.1 M FeCl3 to the diluted mixture of
0.001 M FeCl3(aq) and 0.1 M KSCN(aq). Refer to the equation in step 1 and explain your observations in terms of LeChatelier’s Principle.-- It gave a lighter yellow tint to the dark maroon original color.??

I DONT UNDERSTAND THE EQUATIONS PART OF THIS LAB

Answer 1

The equation that explains the reaction and is given in the problem is

Fe³⁺(aq) +6SCN^-(aq) <--> Fe(SCN)₆^3-(aq)

To better understand the equation you should be aware that the compound that you are forming is a coordination complex the structure is

where the NCS binds to iron threough the nitrogen.

It is stepwise reaction depending on the solvent.

Fe³⁺ + SCN^- <-> FeSCN²⁺

FeSCN²⁺ + SCN^- <-> Fe(SCN)₂⁺
Fe(SCN)₂⁺ + SCN^- <-> Fe(SCN)₃
Fe(SCN)₃ + SCN^- <-> Fe(SCN)₄^-
Fe(SCN)₄^- + SCN^- <-> Fe(SCN)₅^2-
Fe(SCN)₅^2- + SCN^- <-> Fe(SCN)₆^3-

Hope the equation is clear now and hope you have the answers to the rest of the questions.