Week 1 Experiment Answers PDF

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WEEK 1 EXPERIMENT ANSWER SHEET Please submit to the Week 1 Experiment dropbox no later than Sunday midnight.

SUMMARY OF ACTIVITIES FOR WEEK 1 EXPERIMENT ASSIGNMENT   

Experiment 1 Exercise 1 – The Scientific Method Experiment 1 Exercise 2A – pH of Common Solutions Experiment 1 Exercise 2B -- pH and Buffers

Experiment 1 Exercise 1: The Scientific Method Be sure that you have read over the introductions to this week’s Experiments activities before starting. When ready, open the following website: Glencoe/McGraw Hill. No date. The Scientific Method http://www.glencoe.com/sites/common_assets/science/virtual_labs/ES01/ES01.html

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)

Updated October 2013

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 (2 pts). If the compost pile contains a lot of green and brown materials as well as plenty of water and aeration, it will become efficient. 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 (2 pts) Brown to Green Balance

Water Concentration

Number of Turns per Month

Experiment 1

50/50

40-60

4

High

Experiment 2

25/75

0-100

0

Low

Experiment 3 (Optional)

Questions Updated October 2013

Efficiency (High, Medium, Low)

2. Was your prediction correct? If not, why do you think so (2 pts)? My prediction was correct. I added the same amount of green and brown materials as well as plenty of water and air which led to the results that I predicted. 3. Write an alternative hypothesis regarding an alternative compost pile design (2 pts). If I add 25% brown materials and 75% green materials, while adding the minimum amount of water and air, then the compost pile will be inefficient. 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 (2 pts)? The result was a low efficiency level for the compost pile.

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 1 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 pts). hemi c al c ompoundt hatr el eas esH+ The definition of acid according to our textbook is: ”Ac

( hydr ogeni ons)t oas ol ut i oni scalled an acid.” (Reece, Eric J. Simon; Jean L. Dickey; Jane B. P31) An example of an acid would be lemon juice.

Updated October 2013

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. (2 pts). According to our textbook: “ Abas e( oral k al i )i sacompoundt hatac c ept sH+i onsand r emov est hem f r om as ol ut i on. ”(Reece, Eric J. Simon; Jean L. Dickey; Jane B. P31 An example of a base would be bleach. Open the pH simulation below to begin: Glencoe/McGraw Hill. No date. pH of Common Solutions http://www.glencoe.com/sites/common_assets/science/virtual_labs/E22/E22.html 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 (6 pts). Substance

Predicted pH

Explanation for Prediction

Measured pH

1

Stomach acid

2

Needs to be acidic to break down food

2

2

Tomato

5

Slightly acidic but not as much as lemon

4

3

Oven cleaner

10

Contains alkali to clean

Orange juice

8

More acidic than tomato but less than lemon

4

Pure water

7

This is what our body contains most of

7

Vinegar

5

Used for cleaning but also safe for consumption

3

4 5 6

Optional additional solutions 7 8 9 10 11 Updated October 2013

13

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 (1 pts)? Stomach acid, tomato and vinegar 4. Which of your substances tested are considered a base (1 pts)? Oven cleaner and orange juice. 5. What surprised you most about your results in this activity (1 pts)? I thought that orange juice would be more of an acid based off the fact that its an acidic fruit.

Experiment 1 Exercise 2B: Buffers Before beginning, answer the following question: Question Updated October 2013

1. What is a buffer and briefly, how do they work? Cite your source (2 pts)? The buffer is described in our textbook as: “substances that minimize changes in pH by accepting H+ when that ion is in excess and donating H+ when it is depleted.” (Reece, Eric J. Simon; Jean L. Dickey; Jane B. P32) They work by adding hydrogen ions when the Ph level is becoming too acidic and adding hydroxide ions when it is becoming more of a alkali base. This is done to try and maintain homeostasis in the solution.

Procedure Watch the following simulation and answer the questions after watching. https://www.youtube.com/watch?v=ZLKEjXbCU30

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 (4 pts). The green bar drops and the purple bar rises when hydrogen ions are added to the solution. This is because the buffer resisted the change by removing the H+ from the solution in order to maintain homeostasis.

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 (2 pts)? When the HCl is added, the acidic levels rise because of the buffer reaction. I know this because the bar for the acetic acid rises.

4. What will happen to the pH if HCl is added after all of the acetate is used up? (1 pts)? If the HCl is added after the acetate is used up, it will become purely acetic acid since there is no longer any acetate to buffer.

5. What is formed when sodium hydroxide is added and how does this affect the pH (4 pts)? The sodium hydroxide reacts with the acid component of the buffer and causes the pH level to become more alkali base.

Week 1 Experiment Grading Rubric Updated October 2013

Component

Expectation

Experiment 1 Exercise 1

Demonstrates an understanding of the Scientific Method and an ability to apply it (Table 1, Questions 1-3)

10 pts

Experiment 1 Exercise 2A

Demonstrates an understanding of pH and how it applies to your everyday life (Table 2, Questions 1-5).

13 pts

Experiment 1 Exercise 2B

Demonstrates an understanding of pH and the effect of buffers (Questions 1-5)

13 pts

TOTAL

Updated October 2013

Points

36 pts...