Chemistry lab

EXPERIMENT 2: 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 attrac- tion 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.

PROCEDURE

1. Rinse the penny in tap water.

2. Thoroughly dry the penny with a paper towel.

3. Put the penny head-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 1, Trial 1 on the Experiment 1 Data

Sheet.

6. Use a pipette to draw up 2 mL of water, and carefully drop individual drops of water onto 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 1, Trial 1 on the Data Sheet.

9. Repeat Steps 5–8 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 trial. Record your results in Table 1,

% Error column on the Data Sheet.

11.Clean up your work area, and complete the Post-Lab questions.

Experiment Inventory

Materials Graph Paper

*1 Penny

*Tap Water

*1 Paper Towel

*Camera (Camera phone is fine)

Labware 100 mL Beaker

Pipette

Experiment 2Using the Scientific Method

Note: You must provide the materials listed in *red.

DATA ANALYSIS

To complete the last column in Table 1, determine how accurate your hypothesis was compared to your actual data. This can be calculated using the percent error formula:

MAKING A BAR GRAPH

Using the data from Table 1, create a bar graph of your experimental results in the following way:

1. Determine the labels of each axis. We have two pieces of data: the actual number of drops of water that you counted, and the trial number (total of five). The independent variable is the variable that is completely unchanged by any out- side factor, and it will reside on the x-axis. The dependent variable is what you measured in the experiment, and it will go on the y-axis.

2. Determine the range of the data. Your x-axis should be labeled 1, 2, 3, 4, 5 (for the five trials 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).

3. 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 “Number of Drops.” The x-axis should be labeled “Trial Number.”