Introduction
Learning about the scientific method is almost like saying that you are learning how to learn. You see, the scientific method is the way scientists learn and study the world around them. It can be used to study anything from a leaf to a dog to the entire universe. In this lab, we’re going to use the steps of the scientific method to investigate the properties of water; in particular, the rates of evaporation.
Materials Needed:
• 1 measuring cup (250 mL or larger)
• 1 loaf (or similarly shaped) pan that can hold 250 mL of fluid
• 1 coffee mug
• Water
• 2 paper towels
• 2 plastic plates
• Digital camera
Procedures:
Follow the instructions below to complete the two lab experiments. Read over all the directions before you begin. This lab will take at least 5 days to complete. Please be warned that some homework questions are hidden within the laboratory instructions.
Part I: Measuring Evaporation in Kitchen Containers
1. Develop a hypothesis: A hypothesis is a testable answer to a scientific question. It should evaluate the relationship between an independent variable (characteristic or quality that’s unique to the experimental group) and another dependent variable (a quality whose value depends on that of another). This statement can be tested in a controlled experiment, and the results can either support or reject said hypothesis. When a considerable number of related hypotheses are supported, then they can become a theory. Therefore, a theory is an explanation of the natural world which is grounded in experimental evidence.
A. Example: Regular access to fertilizer (independent) increases (implied relationship between both variables) the growth rate (dependent) of potted plants.
2. Develop a prediction: A prediction is a quantitative statement that forecasts the projected results of an experiment. It should include the original hypothesis, and a short description of your experimental model. It utilizes an “If, then” statement to predict what will happen. If the hypothesis is accurate, then the independent variable should measurably impact the dependent variable in a certain way.
A. Example: If regular access to fertilizer increases plant growth, then fertilized plants (experimental group) should grow taller than unfertilized plants (control group).
3. Hypothesis Construction: Before you begin, you should develop a hypothesis. It should be short, and it should assess the relationship between container width (independent) and evaporation rate (dependent). Write down your hypothesis on the line provided below (Hint* Don’t use ambiguous words like affect, impact, or alter).
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4. Prediction Practice: With your hypothesis in-hand, it’s time to predict your experimental results. Which container (loaf pan or coffee mug) should experience a faster evaporation rate? Write down your prediction on the line provided below. Also, use an “If, then” statement for this part. For example: “If wider surface areas ________ evaporation rate, then ________ containers should lose water faster than ________ containers. Please copy this prediction into the first “results section” to receive five points.
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5. Measure out 250mL of water and pour it into the loaf pan.
6. Measure out the same amount of water and pour it into the mug.
7. Place both containers in a sunny place, preferably indoors.
8. Measure the volume of water in each container once a day for five consecutive days. To measure volume, pour the water from the loaf pan back into the measuring cup, record the volume in milliliters (mL), then return the water to the loaf pan. Repeat the process with the mug. Note: Do not measure the depth of the water and don’t spill anything!
9. On each of the five days, take a selfie alongside both of your containers.
10. Table Generation: Use Microsoft Word to illustrate your experimental data with a table. Your table should include the following features: a descriptive title that references both variables (container surface area and water loss), column labels, row labels, and a reference to your measured units (mL). If you’re unfamiliar with table construction, then please follow the provided instructions.
A. Open a Microsoft Word file.
B. Click on the “Insert” heading on the top-lefthand corner of the screen.
C. Click on the “Table” icon and choose an appropriate number of columns (vertical boxes) and rows (horizontal boxes). For this activity, I use six columns by four rows.
D. Fill the data table with accurate information and appropriate labels.
11. Line Graph Construction: Use Microsoft Excel to create a line graph (also called a Figure) showing the rate of evaporation (change in volume over time) with your data from the five days. Your finished product should include the following: “Day of Experiment” as the X-axis, “Volume in mL” as the Y-axis, a descriptive title, and legend. Your legend should include both of your groups (the loaf pan and the coffee cup).
For help building a graph in Excel 2019, watch the video How to Make A Line Graph In Excel 2019 (opens new window).
For help building a graph in Excel 2016, watch the video How to Create A Line Chart In Excel (opens new window).
PART 2: Simulating Evaporation from Leaves
1. Develop a hypothesis: Our previous activity assessed the relationship between container width and evaporation rate (process of turning from liquid into vapor). As liquid water encounters warm air, atmospheric energy is absorbed into hydrogen bonds. This added energy breaks the bonds, causing water to shift from its liquid state to its gaseous one. As you would expect, a wider container (loaf pan) has more surface area exposure than a deeper one (coffee cup). As a result, more energy is absorbed per second and more water is vaporized. Use what you learned from Part One to hypothesize and predict your next endeavor. Which leaf morphology will experience a faster evaporation rate: a broad leaf or one that is needle-shaped? Please copy your prediction into the second “results section” to receive five points.
2. Place a paper towel flat onto a plastic plate. This represents a tree’s flat, broad leaf.
3. Tightly roll up one paper towel lengthwise on another plastic plate. This represents the needle-shaped leaf.
4. Pour 25 mL (0.1 cup) of water evenly over each paper towel.
5. Observe both paper towels: How wet does each paper towel look and feel? Record your observations in the labeled space below.
6. Take a picture of your setup; your face must be visible in this image. Paste your picture into the labeled space below.
7. Place both plates in a sunny spot. Leave for three hours.
8. After three hours, observe the paper towels again. Record your observations.
Part I Results
A. Copy your initial prediction (“If, then statement”) from Part I and paste it beneath this sentence.
B. Results Section: What did you observe over the five days? Did your data support or reject your initial hypothesis? You are encouraged to cite your collected data within this answer.
Analysis Questions:
1. From which container did water evaporate faster: the loaf pan or the mug (Experiment 1)? Use your graph and experimental evidence to explain your answer.
2. Which paper towel retained more water after three hours (Experiment 2)? Reference your original hypothesis here.
3. A hypothesis can be supported (by experimental evidence), but it cannot be “proven”. What does it mean?
4. Define the following terms in your own words: independent variable (1), dependent variable (2), controlled variables (3), experimental group (4), level of treatment (5), and control group (6)?
5. What is the difference between a hypothesis and a scientific theory? Please explain in your own words.
Experimental Design Quiz:
Use the following information to answer questions one through five Biologists noticed that rock climbers compress and dislodge soil from cracks and crevices as they climb. To determine if rock climbing negatively impacted land snail populations on cliffs, researchers surveyed rock cracks and crevices for snails. They studied heavily used climbing routes and areas that were never climbed. Snail densities on heavily used climbing routes were much smaller (20%) than areas with no climbing (McMillan et al. 2003).
1. Develop a reasonable prediction (If…then statement) around their experimental hypothesis.
2. Which is the control group from this investigation?
3. What is the experimental group from this investigation?
4. What is the independent variable from this investigation?
5. What is the dependent variable from this investigation?
Grading Rubric:
Part I Hypothesis and Prediction: 0 – 5
Student failed to generate a prediction for Part I = 0
Student generated an inaccurate prediction (didn’t address surface area or water volume) = 2.5
Student successfully generated an experimental prediction for Part I which included both variables of interest = 5
Part II Hypothesis and Prediction: 0 – 5
Student failed to generate a prediction for Part II = 0
Student generated an inaccurate prediction (didn’t address surface area or water volume) = 2.5
Student successfully generated an experimental prediction for Part II which included both variables of interest = 5
Data Table: 0 – 15
Student failed to generate a data table or another meaningful graphic for Part I = 0
Student generated an illustrative graphic (figure, histogram, or scatterplot), but he/she didn’t provide a table = 5
Student provided a data-rich table, but it didn’t include labels and titles = 10
Student provided a data-rich table with all the required labels and titles = 15
Figure (Graph): 0 – 15
Student failed to generate a line graph for Part I = 0
Student generated an illustrative graphic (histogram of some sort), but he/she didn’t provide a line graph = 5
Student illustrated his/her data with a line graph, but it was missing something (labels, titles, units, and a legend) = 10
Student illustrated his/her data with an exemplary line graph. The figure had all relevant titles and labels = 15
Observations: 0 – 5
Student failed to describe his/her observations from Part II.
Student adequately described his/her observations from Part II.
Analysis Questions: 0 – 20
Each question is worth 4% credit. A student that accurately answers all five questions would receive full credit.
Experimental Design Quiz: 0 – 20
Each question is worth 4% credit. A student that accurately answers all five questions would receive full credit.
Photo documentation: 0 – 15
Students are required to provide six captioned images for this assignment. This includes five pictures from Part I and one picture from part II. A student that fails to upload any images would not receive credit.
Students that provide six images without captions would only receive half credit
Students that provide six captioned images, but the captions are incomplete would receive partial deductions
Students that provide six accurately, captioned images would receive full credit