Which of your substances tested are considered an acid

Question

Experiment Exercise 1: The Scientific Method

Scenario

You have been tasked to design the most efficient compost pile possible; one that can take organic waste material and quickly break it down into a form that can be applied as mulch. A compost pile typically involves:

• Green materials (e.g., fresh grass clippings, fresh leaves)
• Brown materials (e.g., dried grass, twigs, hay, dried leaves)
• Water
• Aeration

The efficiency of a compost pile is measured by how quickly organic matter is decomposed and this efficiency is dictated by the proper combination of the components listed above. Unfortunately, you do not know where to begin! Fortunately, you have a compost simulator that will allow you test a variety of compost designs before you have to construct your actual compost pile.

The purpose of this exercise is to use the Scientific Method to determine the best design for the most efficient compost pile. Note that the parameters that can be varied (using the slider bar) in our simulator are:

• Brown to Green Balance: 100% Green material, 100% Brown material or a combination of both
• Water Concentration: 0 to 100% water
• Number of turns per Month: 0 to 8 turns per month (the greater the number of turns the greater the aeration)

Hypothesis

We will start with the hypothesis that "an efficient compost pile needs lots of green material, a lot of water and a lot of aeration to be efficient".

Question

1. Based on the on the hypothesis above and knowing the design parameters, write a reasonable prediction if the hypothesis is correct. Be sure to word it as an "If...then" statement.

Procedure

A. Conduct an experiment (Experiment 1) to test the hypothesis above using the simulation program.

a. Set the design criteria using the sliders for Brown to Green Balance, Water Concentration and Number of Turns per month. Be sure to use settings based on the hypothesis; this is what you are testing.

b. Record your design criteria in Table 1 below for Experiment 1.

c. Click on the Calendar (Sept 1) in the simulation to start the experiment. When complete, record the Efficiency Meter reading.

Table 1. Design criteria and experiment results

	Brown to Green Balance	Water Concentration	Number of Turns per Month	Efficiency (High, Medium, Low)
Experiment 1
Experiment 2
Experiment 3 (Optional)

Questions

2. Was your prediction correct? If not, why do you think so?

3. Write an alternative hypothesis regarding an alternative compost pile design.

4. Conduct another Experiment (Experiment 2) to test your new hypothesis using new design criteria (Click Reset to start over). Enter the necessary information in Table 1 above. What was the result of Experiment 2?

Optional

If your second design was still not very efficient, conduct another Experiment and record your design criteria and results in the Table above.

Experiment Exercise 2A: pH of Common Solutions

Be sure that you have completed your text book readings, have read through the online lecture and have read the introductory material for the Week 1 Experiment before starting. First, answer the following questions:

Questions

1. What is the definition of an acid? Your definition should include more than just a pH range. Provide one example of an acid. Cite your sources.

2. What is the definition of a base? Your definition should include more than just a pH range. Provide one example of a base. Cite your sources.

Procedure

A. Record the six substances shown across the top of the screen in Table 2 below (e.g., antacid, shampoo, battery acid, soft drinks...).

B. Enter a predicted pH value for each solution and a brief explanation for your choice.

Table 2. Predicted and measured pH values and your explanations.

	Substance	Predicted pH	Explanation for Prediction	Measured pH
1
2
3
4
5
6
Optional additional solutions
7
8
9
10
11
12

C. Next, use the pH paper to measure the pH of each of the six solutions.

a. Click on the lose end of pH paper and drag into the first test tube.

b. It should change color. Drag the piece of paper over to the dispenser and use the color chart to estimate the pH. Record the measured pH in the Table above.

c. Use the up and down arrows beneath the name of the substance and set the value to the one you determined using the pH paper.

d. Repeat this procedure for the remaining five substances.

D. When you have recorded your pH values and set the counter to indicate the measured pHs, click on Check to see how you did. If necessary, retest any solutions you got wrong.

E. This simulation has twelve different solutions. Feel free to test them all if you would like. This is not required though! Click on Reset if you are interested.

F. When you are done testing the pHs, answer the questions below.

Questions

3. Which of your substances tested are considered an acid?

4. Which of your substances tested are considered a base?

5. What surprised you most about your results in this activity?

Experiment Exercise 2B: Buffers

Before beginning, answer the following question:

Question

1. What is a buffer and briefly, how do they work? Cite your source?

Procedure

Open the buffer simulation below to begin (if necessary, copy the web address and past it into your browser). Be sure your speakers are turned on.

A. Listen to the Introduction. If you need to listen to it again, reload the page.

B. Next, click on the Add Strong Acid, H+ button. Pay attention to the bars in the graph. They correspond to the level of the components in the beaker. You will need to watch them carefully.

Questions

2. Why does the green bar in the graph drop? Why does the purple bar in the graph rise? Explain what is occurring chemically.

3. In the simulation shown, what happens to the pH in the beaker when HCl is added? How do you know this based on what you see in the graph?

4. What will happen to the pH if HCl is added after all of the acetate is used up?

Procedure (continued)

C. Next, click on the Add Strong Base. OH-.

Question

5. What is formed when sodium hydroxide is added and how does this affect the pH?