Questions
Do different liquids have different degrees of surface tension?
What effect do dissolved substances have on the surface tension of water?

Materials
 

penny	dropper	rubbing alcohol
table salt	water	liquid detergent
other solutions?

Procedure

1. Predict how many drops of water a penny will hold on its face.  Write down your prediction in your lab notebook.
2. Each student gets a penny.  Put it on a piece of paper towel and add water drop-wise.  Try to keep the drop size as constant as possible.  Count the number of drops until the water drips off the penny.  Record your observations in your lab notebook.
3. Repeat steps 1 and 2 with the following:
1. a solution of 6 mL water and 1 mL alcohol
2. a solution of 5 mL water and 2 mL alcohol
3. a solution of 5 mL water and a few grams of salt
4. a solution of 5 mL water and 0.5 g of salt
5. a solution of 10 mL water and a small drop of liquid dish detergent

1. Which liquids have the strongest surface tension?  The weakest?  How do you know?
2. How do dissolved substances affect the surface tension of water?
3. Did you find any relationship between the ability of a penny to hold more liquid and the shape the liquid takes as more is added?

[Surface Tension score sheet][MHS Chem page]