Chemistry/Equilibrium Minilab
In this "quick–and–dirty" experiment, we will study the reaction: Fe3+(aq) + SCN–(aq) ---> FeSCN2+(aq) .
The FeSCN2+ is red in aqueous solutions.
Procedure and Observations and Analysis and Everything:
1. Mix about 25 mL of 0.002 M KSCN and 25 mL of water in a beaker.
Description of the solution: ________________________________________________
The ions present in KSCN(aq) are: ___________________________________________
Obtain a solution of 0.2 M Fe(NO3)3.
Description of the solution: ________________________________________________
The ions present in Fe(NO3)3 (aq) are: ________________________________________
2. Add 5 drops of the Fe(NO3)3 solution to the beaker, and mix.
Description of the solution: ________________________________________________
What TWO pairs of ions might be responsible for the colour change after adding Fe(NO3)3? _____________________________________________________________________
3. Observe a solution of KNO3.
Description of the solution: ________________________________________________
Could the ions present in KNO3 be responsible for the observations in #2? Why?
____________________________________________________________________
4. Considering your answer to #3, what pair of ions MUST be responsible for the change noted in #2? ________________________________
5. Divide the beaker contents equally among 4 evaporating dishes. Save the solution in one of the dishes to act as a reference for colour comparison purposes.
6. To one of the dishes add a few crystals of solid KSCN. Observe, stir and observe again.
Observations: __________________________________________________________
a) What effect did the addition of KSCN(s) have on the [SCN–] in solution after stirring?_________________________________________________________________
b) What VISIBLE effect did the addition of KSCN(s) have on the [FeSCN2+]? (FeSCN2+ is the red ion produced in the reaction.)
_________________________________________________________________
c) Was Fe3+ present in excess before you added the KSCN(s)? How do you know?
_________________________________________________________________
_________________________________________________________________
7. Add an extra 3 drops of Fe(NO3)3 to another evaporating dish of solution.
Observations: _________________________________________________________
a) What effect did the addition of Fe(NO3)3 have on the [Fe3+] in solution after stirring?
_________________________________________________________________
b) What effect did the addition of Fe(NO3)3 have on the [FeSCN2+]?
_________________________________________________________________
c) Was SCN– present in excess before you added the Fe(NO3)3? How do you know?
__________________________________________________________________
__________________________________________________________________
8. Compare what you wrote for #6(c) and #7(c). Suggest how you might account for these results.
9. Add a few crystals of Na2HPO4 to another evaporating dish of liquid. Observe for a minute and then stir. Fact: Fe3+ and HPO2- 4 form an almost completely insoluble solid having a translucent white colour.
Observations: __________________________________________________________
a) What effect does the addition of HPO2- 4 have on the [Fe3+] IN SOLUTION?
_________________________________________________________________
b) What effect does the addition of HPO2- 4 have on the [FeSCN2+]?
_________________________________________________________________
c) What would have to be true about the reaction: Fe3+ + SCN– ---> FeSCN2+ in order for your statements in #9(a) and (b) to be make sense?_________________________________________________________________
Let’s summarize our findings:
a) What happens to the concentration of the product if you increase the concentration of a reactant?
If a reaction starts at equilibrium, which side will it "shift" to if the concentration of a reactant is increased?
b) What happens to the concentration of the product if you decrease the concentration of a reactant?
If a reaction starts at equilibrium, which side will it "shift" to if we decrease the concentration of a reactant?
