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Activity: Water and Electrostatic Forces

The polar covalent bonding of hydrogen and oxygen in water results in interesting behavior, such as water’s response to electrostatic forces. In this activity you will explore the electrostatic forces on liquids.
 
Materials
  • Water faucet with running fresh water
    • *Note* If a faucet is not available, you can use two cups and a pin or other sharp object. 
  • Plastic comb (preferably one with many small teeth, like a pocket comb)
Optional
  • glass rod
  • piece of silk or nylon
Procedure
  1. Predict what will happen to the stream of water of when
    1. An electrostatic charge is brought near it.
    2. Record your predictions on Table 3-1 using the terms repel, attract, and no reaction.
  2. 2. Determine what happens when an electrostatic charge is brought near the stream of water. Record your observations in Table 3-1.
    1. Adjust your faucet to make a very thin flow of running water. See Fig. 3-3a.
      1. Alternatively, make a hole in one of the paper cups using the pin.  Adjust the size of the water flow from the hole so that a thin, steady stream comes out.  Use the second cup to catch your flow of water.  See Fig. 3-3b. 
    2. Put an electrostatic charge on a comb by running it through dry, greaseless hair. 
    3. Bring the charged comb near the stream of water. Observe what happens to the water.
  3. Optional. See if you can observe the reaction when a positive (+) electrostatic charge is brought near the stream of water.
    1. Put a positive (+) charge on a glass rod by rubbing it with silk or nylon. Note that positive charges are more difficult to observe, especially in humid environments.
    2. Bring the charged rod near the stream of water. Observe what happens to the water.
    3. Record your results below in Table 3-1.
 
<p>a.</p> <p>b.</p>Fig. 3-3: Determining the apparent charge on water. Part (a) shows the use of a running faucet of water, and part (b) shows the modification using two cups.
 
Table 3-1: Interactions between a flowing stream of water and electrostatic charges
  Movement of Water
Object Predicted Observed
Charged Comb    
Charged Glass Rod    

 

Activity Questions: 
  1. How do your observations of the interaction between the stream of water and electrostatic charge on the comb show that water is a polar substance?
  2. Why might seawater act the same way as water?
  3. How do you think a nonpolar liquid would respond to a charged object if you were able to repeat the experiment (using a stream of nonpolar liquid and observing its reaction to a charged comb)?
  4. In this experiment we used a plastic comb, which tends to take on a negative charge when rubbed on hair. How do you think your observations might have been different if you had used a positively charged item instead of the negatively charged comb?
  5. If you did try to make a positive charge using the glass rod, how do your observations of the interaction between the stream of water and electrostatic charge on the glass rod show that water is a polar substance?
Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.