Liquid Cohesion and Surface Tension

Name: ____________________________________

Date: _____________________________________

BIOL 1014 Lab 3 Cohesion of Water                                          

Skill: Liquid Cohesion and Surface Tension

Before starting the lab, fill in the hypothesis on how many drops of water will fit on a penny. You must answer the hypothesis before beginning the lab. The hypothesis prediction is worth four points.

Hypothesis: How many drops of water can fit on one side of a penny? _____

Part A: Perform a CONTROL test for comparison with later results.

Step 1: Rinse a penny in tap water and dry completely. This is your “clean” penny.

Step 2: Place the penny on paper towel.

Step 3: Use an eye dropper to place drops of WATER on the penny (one at a time) until ANY amount of water runs over the edge of the penny. Stop

4: Record the number of drops for that trial in the table.

Repeat Steps 1 - 4 three more times before calculating your average.

Average = Trial 1 + Trial 2 + Trial 3 + Trial 4

            4

Part B: Perform tests with the **Treated Penny. (Instructions for treating penny appear below) 

Treated Penny:   

Step 1 - Start with a “clean” penny. Rinse the penny in tap water and dry completely. Be sure to remove as much residue as possible - without using soap!  

Step 2 – Hold the penny with the tweezers, then dip it into a mixture of ¼ liquid dish soap, ¾ water.  Note brand of liquid dish soap used below.  Allow extra liquid to drip off the penny into the container before proceeding to the next step.

Step 3: Place penny on dry spot on a paper towel. Place drops of PLAIN WATER on the penny (one at a time) until ANY amount of water runs over the edge of the penny.

Step 4: Record your observations and the number of drops for that trial in the table.

Brand of Dish Soap Used in Treatment:  ________________________

Repeat Steps 1 - 4 three more times before calculating the average.

BIOL 1014 Lab 3 Cohesion of Water

Part C: Perform tests with the Alternative Liquid. (Options for alternative liquids are below, please include which liquid you chose in the data table.)

Alternative Liquids: Choose from either rubbing alcohol, vinegar or Windex

Treated Penny:  

Step 1 - Start with a “clean” penny. Rinse the penny in tap water and dry completely. Be sure to remove as much residue as possible - without using soap! 

Step 2: Place the penny on paper towel.

Step 3: Use an eye dropper to place drops of Alternative Liquid on the penny (one at a time) until ANY amount of the liquid runs over the edge of the penny.

Step 4: Record the number of drops for that trial in the table.

Alternative Liquid Chosen: ____________________________

Repeat Steps 1 - 4 three more times before calculating the average.

 Analysis Questions

1. Explain your results from all three parts of the experiment in terms of cohesion and surface tension.  Refer to your text book for information on cohesive and adhesive properties of water.
2. Why are multiple trials of each experiment completed and averages calculated?

1. Provide at least 2 possible reasons for any differences you observed between trials 1-4 within each of the three parts of this lab.