Experiment 1: Using the Scientific Method
This experiment will allow you to demonstrate your understanding of the scientific method. Did you know that water tends to form beads or drops. This ability of water molecules to stick together, a property known as surface tension, is due to the mutual attraction of water molecules. One side of each water molecule has a slight positive charge; the other side has a slight negative charge. The attraction of two molecules is maintained by a hydrogen bond. The high surface tension of water forms a kind of ''skin'' on the surface.
Preliminary Procedures
Read through the entire lab TWICE. Formulate a mental picture of what you will be doing before you start. If you have any questions before you proceed, go to the Student Portal and seek out the answers and/or contact technical support. You can reach technical support by phone at 1-888-ESL-Kits (1-888-375-5487) or by email at.
You should also make your work space free from clutter and distractions. Following good laboratory safety procedures and protocols, e.g. wearing the appropriate clothing, tying back your hair, wearing safety glasses, and following the procedure steps carefully, etc., helps to insure both reliable, as well as reproducible, results.
Procedure
1. Rinse the penny in tap water.
2. Thoroughly dry the penny with a paper towel.
3. Put the penny heads side up on a clean, dry, flat surface.
4. Fill your 100 mL beaker with 50 mL of tap water.
5. Predict the number of drops that you think will fit onto the head of the penny in Table 3: Trial #1.
6. Use a pipette to draw up 2 mL of water and carefully drop individual drops of water onto the head of the penny.
7. Count the number of drops until the water spills over the edge of the penny.
8. Record the actual number of drops in Table 3: Experimental Results for Trial 1.
9. Repeat Steps 6 - 8 for a total of five trials. Make sure you thoroughly dry your penny between trials.
10. In the Data Analysis section, calculate how accurate your predictions were for each trials. Record your results in Table 3: Percent Error.
11. Clean up your work area, and complete the Post-Lab questions.
Table 3: Number of Drops of Water that Fit on a Penny
|
Trial
|
Predicted # of Drops
|
Actual # of Drops
|
% Error
|
|
1
|
|
|
|
|
2
|
|
|
|
|
3
|
|
|
|
|
4
|
|
|
|
|
5
|
|
|
|
|
Average
|
N/A
|
|
|
Data Analysis
To complete the last column in Table 3, determine how accurate your hypothesis was as compared to your actual data. This can be calculated using the percent error formula:
Making a Bar Graph
Using the data from Table 3, create a bar graph in the following way:
1. Determine the labels of each axis. We have two pieces of data: experimental results, which are the actual number of drops of water that you counted from five different trials. The dependent variable is the variable that is completely unchanged by any outside factor. The dependent variable, will reside on the x-axis. This means that the experimental results will reside on the y-axis.
2. Determine the range of the data. Your x-axis should be labeled 1, 2, 3, 4, 5 (for the 5 trails that you conducted). The range for the actual number of drops (experimental results on the y-axis) should start at zero and go up to include the maximum number of drops that you counted. Remember to evenly space your numbers on the y-axis, e.g. 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50.
Put it all together and draw your bars to signify the number of drops that you counted in each trial.
You may wish to perform this step using a graphing program.
Hint: The Y-Axis should be labeled Experimental Results. The X-Axis should be labeled Trial Number.
Post-Lab Questions
1. Why did you perform more than one trial?
2. What are the benefits of repeated trials?
3. Take a picture of your Bar Graph and send it to your instructor with your Post-Lab Questions.