Lab: Modifying the Equilibrium State
Although you will not be working with actual chemicals during this laboratory since you will be doing it virtually, the procedure is given in order for you to be aware of the process that would be followed in a laboratory setting.
Material
Chemicals
Sealed NO2 tubes, KSCN solution (0.002 M), acidified Fe(NO3)3 solution (0.2 M), KSCN crystals, Fe(NO3)3 crystals, KOH (concentrated (8 M)), distilled water
Apparatus:
Bunsen burner, ring stand, wire gauze, matches, thermometer, dropper, test tubes, glass stirring rod, beaker tongs
Safety
Safety goggles and a lab apron should always be worn when working with chemicals.
This lab will be performed using small quantities of chemicals (micro-scale chemistry).
Procedure
Part A:
Fill a 600 mL beaker to the 3/4 mark with water. Bring to a boil using a Bunsen burner.
In another 600 mL beaker, fill to the 1/2 mark with water; add ice in order to lower the temperature to about 0°C.
Note the room temperature.
Observe the NO2 thoroughly at room temperature.
Place the sealed NO2 tube in the cold bath. Note your observations.
Remove the test tube from the cold bath.
Let the test tube stand until it reaches room temperature. Note your observations.
Place the test tube in the hot bath. Note your observations.
Remove the test tube from the hot bath.
Let the test tube stand until it reaches room temperature. Note your observations.
Part B:
Place 50 mL of KSCN solution in a 100 mL beaker.
Add 6 drops of Fe(NO3)3 solution.
Stir with a glass rod.
Note your observations.
Pour about 10 mL of this solution into 5 test tubes.
Test tube #1 will be your control.
In test tube #2, add 2 KSCN crystals. They are sources of (SCN)-. Stir and note your observations.
In test tube #3, add 2 crystals of Fe(NO3)3. They are sources of Fe3+. Stir and note your observations.
In test tube #4, add 2 crystals of KSCN and 2 crystals of Fe(NO3)3. Stir and note your observations.
In test tube #5, add concentrated KOH solution, one drop at a time until a precipitate is formed. Note your observations. Note that Fe3+ reacts with the OH- to produce Fe(OH)3(s).
Compare all test tubes to the control test tube, according to colour (from lightest to the darkest)
Empty all of the test tubes in a 250 mL beaker. Stir and note your observations.
Empty the solution of your 250 mL beaker into another group's 250 mL beaker. Stir and note your observations.
Sample Results
Step A-3: The room temperature is 24°C.
Step A-4: At room temperature, the NO2 is a gas, orange/rust and transparent.
Step A-5: The NO2 becomes a pale orange-yellow colour almost colourless.
Step A-7: The NO2 returns to an orange/rust colour.
Step A-8: The NO2 becomes dark orange.
Step A-10: The NO2 returns to an orange/rust colour.
Step B-1: The KSCN is a liquid solution, transparent and colourless.
Step B-2: The Fe(NO3) 3 is a liquid solution, orange and transparent.
Step B-4: The solution becomes dark orange.
Step B-6: Test tube #1 is dark orange.
Step B-7: The KSCN is a solid, off-white, opaque/crystals.
Test tube #2 is red-orange.
Step B-8: The Fe(NO3) 3 is a solid, colourless and translucent.
Test tube #3 is dark orange.
Step B-9: Test tube #4 is dark red/burgundy.
Step B-10: The KOH is a liquid solution, transparent and colourless.
Test tube #5 contains a yellow/orange precipitate in suspension.
Step B-11: The order from lightest to darkest is test tubes #5, 1, 3, 2, 4.
Step B-12: This mixture is liquid, colourless and contains a red precipitate in suspension.
Step B-13: Same colour as step B-12.
Conclusion
Briefly state the results for the laboratory, in general. This should be no more than two sentences.
Questions
Part A:
Give the balanced chemical equation for this reaction.
When the system is returned to room temperature, does it mean that it returned to its initial equilibrium state? Why?
Give the balanced chemical equation for the reaction between KSCN and Fe(NO3)3.
Using your observations, explain how the equilibrium was affected by adding different reactants to test tubes 2, 3, 4, 5 and the two beakers in steps B-12 and B-13. (Refer to the concentrations of each reactant and product as well as the colour change)
Does the mixture in the 250 mL beaker from step B-13 represent a system in equilibrium? Explain.
5 answers
Briefly state the results for the laboratory, in general. This should be no more than two sentences.
Part A:
Give the balanced chemical equation for this reaction.
When the system is returned to room temperature, does it mean that it returned to its initial equilibrium state? Why?
Give the balanced chemical equation for the reaction between KSCN and Fe(NO3)3.
Using your observations, explain how the equilibrium was affected by adding different reactants to test tubes 2, 3, 4, 5 and the two beakers in steps B-12 and B-13. (Refer to the concentrations of each reactant and product as well as the colour change)
Does the mixture in the 250 mL beaker from step B-13 represent a system in equilibrium? Explain.
1. The balanced chemical equation for the reaction is: 2NO2(g) ⇌ N2O4(g)
2. When the system is returned to room temperature, it does not necessarily mean that it returned to its initial equilibrium state. This is because the reaction may not have enough time to reach equilibrium before it is brought back to room temperature. The system might reach a new equilibrium position or may still be in the process of reaching equilibrium.
3. The balanced chemical equation for the reaction between KSCN and Fe(NO3)3 is: Fe(NO3)3(aq) + 3KSCN(aq) → Fe(SCN)3(aq) + 3KNO3(aq)
4. By adding different reactants to the test tubes and beakers, the equilibrium was affected as follows:
- Test Tube 2: The addition of KSCN crystals increased the concentration of (SCN)- ions, causing the equilibrium to shift to the right and resulting in a darker color.
- Test Tube 3: The addition of Fe(NO3)3 crystals increased the concentration of Fe3+ ions, causing the equilibrium to shift to the right and resulting in a darker color.
- Test Tube 4: The addition of both KSCN and Fe(NO3)3 crystals increased the concentrations of (SCN)- and Fe3+ ions, causing the equilibrium to shift further to the right and resulting in a darker color.
- Test Tube 5: The addition of concentrated KOH solution caused the formation of a precipitate, indicating the shift of the equilibrium to the left, towards the formation of Fe(OH)3(s). This decreased the concentrations of Fe3+ ions and resulted in a lighter color.
5. The mixture in the 250 mL beaker from step B-13 does not represent a system in equilibrium. This is because there is still a red precipitate in suspension, indicating that the reaction has not reached a state of balance. The presence of the precipitate suggests that one or more of the reactants have not been completely consumed and the reaction is still ongoing.
7 answers