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Chemistry II

Laboratory 3 Procedure – Chemical Equilibrium


Chemical equilibrium is dynamic condition that plays an important role in our life since many of food metabolism processes are controlled by equilibrium. A variety of industrial processes are based on the chemical reactions that do not proceed to completion. It is important to know how to manipulate such reactions in order to obtain the maximum amount (yield) of theproduct.

Chemical equilibrium can be disturbed by variety of factors: change of regents’ concentrations, removal of the products, or change of the temperature, just to name a few.

In this lab, we will study the Le Chatelier’s Principle through the observation of the effect of disruptions (such as concentration or temperature) applied to the following reaction, by analyzing its color changes:

[Co(H2O)6]+2 + 4Cl ↔ CoCl4-2 +6H2O

Figure 1: [Co(H2O)6]+2 forms a pink complex, and CoCl -2 is a blue complex.

Cobalt (II) does not exist in aqueous solution as a free ion, however it forms a pink complex with six water molecules. In the presence of chloride ions, different complex is formed, the blue CoCl4-2.

There are few objectives of this lab:

1. To enhance your ability to apply Le Chatelier’sPrinciple.

1. To improve your understanding of the equilibriumconstant.

2. To analyze the responses of the equilibrium constant to the perturbations such as change of concentration ortemperature.

Before you start this laboratory assignment, you are encouraged to review Section 14.1-14.3 and

14.6 on page 487 in the textbook. Throughout this laboratory assignment, you will be required to perform and thoroughly document your calculations pertaining to the stoichiometry associated with the reaction above. Be sure to record all observations and any relevant notes that you think you will need to include in your laboratory report.

Take a moment to formulate and write down a hypothesis describing how the addition of chloride ions, distilled water and silver nitrate will affect the equilibrium of this reaction?

Pre-Lab Questions:

1. State the La Chatelier’sPrinciple.

2. Write the equilibrium constant for the reaction in Figure1.(Note: You are encouraged to use the MS Word equation editorto construct the equilibrium constant for later use in your report.)


Preparing the Lab I

1. From the course home page, click on the Virtual Lab Tutorial link to watch theoverview of using the virtuallab.

2. From the course home page, access the lab environment by clicking on the Virtual Lab


3. After the lab environment loads, click ‘File’ then ‘Load anAssignment.’

4. Select the ‘Chemical Equilibrium’ category.

5. Select the ‘Cobalt Lab’assignment.

6. At this point, you have access to the first experiment with the required supplies to complete yourexperiments.

If you haven’t already done so, formulate a hypothesis about the effect of addition chloride ions, water, and silver nitrate on equilibrium as you will need to include this in your final report.

Performing the Experiment

7. Select the ‘Glassware’ tab in the stockroom. Then, select empty 1000 mL Erlenmeyer flask.

8. Then select the ‘Solutions’ tab in the stockroom, click on ‘Cobalt (II) Chloride Exp Solutions’ transfer Erlenmeyer flask containing 1M CoCl2 to theworkbench.

9. Selectthe‘Stockroom’then‘Solutions’tab,transferErlenmeyerflaskcontaining12MHCl solution to theworkbench.

10. Selectthe‘Stockroom’then‘Solutions’tab,transferErlenmeyerflaskcontaining6M

AgNO3 solution to the workbench

11. Select the ‘Stockroom’ then ‘Solutions’ tab, transfer Erlenmeyer flask containing distilled water to theworkbench.

12. Transfer 25 mL of 1 M CoCl2 into the empty 1000mL Erlenmeyer flask by moving flask with CoCl2 and dropping it onto the empty one. We will now collect some data about this solution.

13. Record the values for the concentration (molarity), and the color of the solution.

14. Add 2 mL of concentrated (12 M) HCl to the 1000mL Erlenmeyer flask. Continue until you see a change in equilibriummixture.Record your observations.

15. Continue adding HCl until no further change occurs. Record yourobservations.

16. Add 2 mL of distilled water to the reaction mixture. Continue until a changeoccurs.Record yourobservations.

17. Continue adding water until no further change occurs. Record yourobservations.

18. After you record your data, clear the workbench but do not close the virtuallab!

Data Analysis

19. Before completing this lab, you will need to conduct a thorough analysis of your data in order to answer the mandatory questions below. You will need to include yourresponses to these questions in your written report in the appropriate section(s). You can use the virtual lab to investigate answers to thesequestions.

a) Imagine the following scenario: a student doing the experiment added 20 mL of silver nitrate, AgNO3, to the blue equilibrium mixture. The reactionmixture become pink and cloudy with white precipitate of silver chloride , AgCl, appearing in the bottom of the flask.Can you explain how those observations are consistent with Le Chatelier’s principle?

b) Imagine the scenario: A student placed pink equilibrium mixture in the hotwater. Reaction mixture changed color toblue.Is the reaction endothermic or exothermic?How the change of the temperature influences the equilibrium of this reaction? Explain.


This section should include notes about any observations or datacollected during the lab.

Report Requirements

This section contains key information that must be included inyour typed report.

1. Define the problem in a manner that is clear andinsightful.

1. Identify the strategies and procedures used during thelab.

2. Clear hypothesis statement and other potential solutions that identify anyrelevant contextual factors (i.e. real-worldcosts).

3. Clear presentation of data including any tables or other figures that are relevant to understanding your stated conclusions at the end of the report. Include anyrelevant calculations performed during thelab.

4. Clearly stated results and discussion of possible improvements to theprocedure.

5. Conclusive statements arguing in favor of yourfindings.

Note: All reports will be graded using the rubric embedded within the course.

Here are some questions to consider as you write your report:

1. Does my problem statement makesense?

1. Have I summarized my strategies/procedures well enough to be replicated by anoutsider?

2. Did I have a valid hypothesis at the start of the lab? Have I expressed this in myreport?

3. Do my tables and/or graphs makesense?

4. Are my conclusions valid based on my supplieddata?

5. Did I thoroughly summarize my laboratory experience in a concise, factual way suchthat the reader can understand my processes and findings in the conclusion sectionalone?

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