Chemistry/Equilibrium Minilab

CHEMISTRY 12 : 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?