Color Change Challenge Lab

Color Change Challenge

Objective: Given four different colorless solutions, can you discover the correct sequence of combining the solutions that will result in specific color changes? What is you were given a limited amount of each solution—could you determine the minimum number of steps required to accomplish the goal?

Background: Scientists use many different strategies to solve problems. One such strategy is known as trial and error. The purpose of trial and error is to test multiple possibilities for solving a problem, but not necessarily to find out why the solution works. The term trial and error may lead some to believe that when a test (the trial) leads to an incorrect solution (the error), then the experiment has failed. On the contrary, the experimenter has gained valuable knowledge—learning what does not work!  Trial and error is often used to discover new medicines and is a great strategy for producing new inventions. Thomas Edison (1847-1931), the famous inventor, once said, “I have not failed. I’ve just found 10,000 ways that won’t work.”

            The activity uses the problem-solving strategy of trial and error to identify a series of chemical changes that will result in specific color changes. A chemical change is defined as a change in the composition and properties of a substance. The transformation of original substances (reactants) into new substances (products) as a result of a chemical change is called a chemical reaction.  Both in the natural world and in the laboratory we recognize that a chemical reaction has occurred by observing the appearance of products with physical and chemical properties different from the reactants from which they were made.

Goal: The purpose of this experiment is to mix four solutions labeled A, B, C and D in the correct sequence to produce a series of color changes—from colorless to orange, then to bluish-black, and finally back to colorless again. The testing procedure should be planned in advance to accomplish this goal in the minimum number of steps possible. Keep in mind that you have a limited amount of solution to test.

Pre-Lab Questions:

1. Starting with the four available solutions (A, B, C, D), how many different combinations of any solutions are possible? (Note: adding solution A to solution B will produce the same result as adding solution B to solution A.)

2. What are signs of a chemical reaction? What will you be looking for in your observations?

3. Working with a partner, write a general outline describing an “action plan” of steps to test the possible combinations of solutions. This action plan can be written as specific numbered steps or as a graphic organizer as a flow chart or other diagram. Allow for more than one possible correct sequence.

Procedure:

1. Obtain a testing tray and place it in the center of your work area.

2. Obtain one of the labeled pipets from the pipet holder. Be careful to not squeeze the bulb until you are ready to dispense the solution.

3. Place 5 drops of the chosen solution into one well of the testing tray. Use the diagram of the spot plate in your lab book to record which solution was placed in the first well.

4. Return the pipet to the pipet holder.

5. Following your action plan then select the second pipet and place 5 drops of the second solution into the same well as the first solution. Stir with a clean toothpick. Record the combination on the diagram. For example A + B.

6. Observe any changes in the color and appearance of the mixture and record your observations in the well on the diagram.

7. Continue with the same general procedure for other combinations of two, three, and four solutions until the correct sequence of colored products is obtained—from two colorless reactants to an orange product, then adding another reactant to any orange solutions to produce a bluish black solution, and finally adding the fourth solution to end with a colorless product.

8. Clean your testing tray as needed.

Post-Lab Questions:

1. Write out the order in which the solutions were combined to produce the desired series of color changes—colorless to orange to dark blue and back to colorless. Could there be more than one correct sequence?

2. The number of wells used is an indication of the number of steps that were needed to discover the correct sequence? Do you think the solution could have been discovered in fewer steps? Why or why not?

3. Adding solution A to solution B would produce the same result as adding solution B to solution A. Would reversing the entire order in which the four solutions were mixed (see Question #1) produce the desired series of color changes? Explain.

4. Briefly describe an everyday situation in which trial and error might be used to explain a problem.