Embedded Files
This lab will go in your lab book. Follow the directions below to complete the lab.
Purpose (put into lab book)
The purpose of this lab is to observe the effect of stress on a system at equilibrium.
Background (read and then answer the questions in your lab book)
Stress is anything that disrupts an equilibrium.
Examples of stress can be changes in pressure, temperature, or amount of a substance (adding or removing a substance).
In order to represent the addition of a substance we draw an arrow pointing downward on the top of the substance. If a substance is removed, we draw an arrow pointing upward on top of the substance.
After a stress is added to an equilibrium, the equilibrium will shift in the forward or reverse direction in order to alleviate the stress.
In order to show the shift in an equilibrium, an arrow is drawn under the reaction either pointing to the left or to the right.
The system at equilibrium you will be studying is:
As you can see above the reactants are pink and the products are blue.
Now answer the following questions in your lab book:
What is stress?
What are two examples of stress?
If you add a substance, how do you show this?
If you remove a substances, how do you show this?
How do you show a reaction is moving in the reverse direction?
Now look at the equilibrium we are studying. If you produce more products, what color will the solution be?
Now look at the equilibrium we are studying. If you produce more reactants, what color will the solution be?
Try this example in your lab book:
An equilibrium shown below is examined. The reactants are pink and the products are clear. It starts as pink and then ammonium chloride is added. The solution turns clear.
First, copy down the equilibrium. Writing pink under the reactant side and clear under the product side.
Second, draw an arrow (in another color) to show we are adding the ammonium ion (that is part of ammonium chloride).
Third, draw an arrow (in another color) across the bottom of the equilibrium to show the color change that occurred.
See me before you continue.
Materials (put in lab book)
Read the procedure below and list all of the materials required to complete this lab. Do not forget to include chemicals and glassware.
Procedure (you do not need to put into your lab book)
Label three test tubes 1-3.
Using the graduated cylinder, measure out 5 mL of the 0.2 M cobalt chloride solution and pour it into test tube 1 and another 5 mL into test tube 2.
Under the fume hood, pour 7 mL of concentrated HCl into test tube 1. Swirl the test tube gently and record observations in your data table. BEFORE CONTINUING COMPLETE THE ENTIRE ROW OF THE DATA TABLE FOR THIS STEP.
Pour approximately half of the contents of test tube 1 into test tube 3.
Add 7 mL of water to test tube 1. Swirl the test tube and record observations in the data table. BEFORE CONTINUING COMPLETE THE ENTIRE ROW OF THE DATA TABLE FOR THIS STEP.
Add 8 mL of 0.10 M silver nitrate to test tube 3. Swirl the test tube gently, and record the results in the data table. BEFORE CONTINUING COMPLETE THE ENTIRE ROW OF THE DATA TABLE FOR THIS STEP.
Measure 10 mL of acetone. Tilt test tube 2 and gently pour the acetone very slowly down the side of the test tube to avoid mixing the acetone and the cobalt solution. It should take you about 2 minutes! This step will not work unless the acetone remains a separate layer. Record results in the data table referring to the top layer only. BEFORE CONTINUING COMPLETE THE ENTIRE ROW OF THE DATA TABLE FOR THIS STEP.
Data (put into lab book)
Click here if you are absent to show pictures from lab.
Note: The Reaction with Arrows column is going to take up a lot of room since you are going to have to write the reaction EACH TIME and draw arrows for each. Click here to see how you should draw the table below in your lab book.
See me before you continue.
Conclusion (put into lab book)
Look at your arrows throughout the lab, look for a pattern and summarize what you see. (DO NOT use the words reactant, product, forward, reverse, left, or right).
Predict the direction shift and the resulting color of the solution if CoCl4-2 is added. (Show the equation and arrows when answering this question.)
Predict the direction shift and the resulting color of the solution if Co(OH2)6+2 is added. (Show the equation and arrows when answering this question.)
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