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.
The results of the laboratory showed that the NO2 gas changed color from orange/rust to pale orange-yellow, then to dark orange when exposed to different temperatures. In the KSCN and Fe(NO3)3 reaction, the color of the solution changed from dark orange to dark red/burgundy when different reactants were added. The mixture in the 250 mL beaker from step B-13 does not represent a system in equilibrium because there is still a red precipitate in suspension, indicating that the reaction has not reached a state of balance.
Conclusion
Briefly state the results for the laboratory, in general. This should be no more than two sentences.
The laboratory experiment explored the effects of temperature on the equilibrium state of NO2 gas and the reactions between KSCN and Fe(NO3)3. The results showed that temperature changes and the addition of different reactants can alter the equilibrium position and color of the substances involved.
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.
Part A:
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.
To answer the questions, let's go through each question one by one and explain how to find the answers:
Part A:
1. Give the balanced chemical equation for this reaction.
To find the balanced chemical equation, we need to know the reactants and products involved in the reaction. In this case, we're observing the behavior of NO2 in different temperature conditions. Based on the observations provided, we can conclude that the reaction is:
2NO2 (g) ⇌ N2O4 (g)
2. When the system is returned to room temperature, does it mean that it returned to its initial equilibrium state? Why?
To determine if the system returned to its initial equilibrium state, we need to consider the forward and reverse reactions of the reaction. In this case, at room temperature, the color of NO2 returned to its original orange/rust color, indicating that the system returned to its initial equilibrium state. This is because the color change corresponds to the shift in the equilibrium position, and when the system reached room temperature, it achieved a balance between the forward and reverse reactions.
3. Give the balanced chemical equation for the reaction between KSCN and Fe(NO3)3.
To find the balanced chemical equation for the reaction between KSCN and Fe(NO3)3, we need to write the formulas for the reactants and products. Based on the provided information, the balanced equation is:
Fe(NO3)3 (aq) + 6KSCN (aq) ⇌ Fe(SCN)6^(3-) (aq) + 3KNO3 (aq)
4. 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 color change)
To answer this question, we need to analyze the observations made in each test tube and beaker. Based on the information provided, here is an analysis of the observations and their effect on the equilibrium:
Test tube 2: Adding KSCN crystals (sources of SCN-) to the solution resulted in a red-orange color. This indicates an increase in the concentration of Fe(SCN)6^3-, shifting the equilibrium towards the product side.
Test tube 3: Adding Fe(NO3)3 crystals (sources of Fe^3+) to the solution resulted in a dark orange color. This indicates an increase in the concentration of Fe(SCN)6^3-, shifting the equilibrium towards the product side.
Test tube 4: Adding both KSCN crystals (sources of SCN-) and Fe(NO3)3 crystals (sources of Fe^3+) to the solution resulted in a dark red/burgundy color. This indicates a further increase in the concentration of Fe(SCN)6^3-, shifting the equilibrium towards the product side.
Test tube 5: Adding concentrated KOH solution resulted in the formation of a yellow/orange precipitate (Fe(OH)3). This indicates a shift in the equilibrium towards the reactants' side, as OH- reacts with Fe^3+ to form Fe(OH)3.
Beakers in steps B-12 and B-13: When the solutions from different test tubes were combined in the beaker and stirred, a red precipitate formed, indicating the formation of Fe(OH)3. This represents a shift in the equilibrium towards the reactants' side.
5. Does the mixture in the 250 mL beaker from step B-13 represent a system in equilibrium? Explain.
Based on the observation that the mixture in the 250 mL beaker contains a red precipitate in suspension, it indicates that the system is not at equilibrium. The formation of the red precipitate suggests that the reaction is still proceeding towards the formation of Fe(OH)3, indicating that the equilibrium has not been reached.