Name______________________________
Observing the Surface Properties of Water
Background
Water is such a common substance that we tend to take it for granted
unless a serious problem like a flood or water shortage occurs. But in science we
can learn a lot about water. As familiar as water is to you in your daily life, you
have probably let the observation of the way in which water particles affect each
other go unnoticed. Today you will be exploring the surface properties of water.
Equipment
- Dropper bottle of water
- A small piece of aluminum foil
- Pencil
- Plastic medicine cup
- 4 test tubes
- 1 test tube rack
- Oil
- Paper clip
- Petroleum jelly
- A piece of string
- Soap
- Salt
- Sugar
- Water
Procedures
1. Use a medicine dropper to add a single drop of water to a small, flat
piece of aluminum foil. Observe the drop from the side, and then draw
what it looks like.
2. How must water particles on the surface of the drop be reacting with each
other to produce this effect?
3. Add a second drop of water so that it is close to the first drop but not
touching it. With the point of a pencil, move one of the drops slowly
toward the other until both drops just barely touch. What happens as the
drops touch?
4. Why do you think this took place?
Drop of water
5. Fill the plastic cup with water until the level is exactly even with the rim
of the cup. Using a medicine dropper, slowly add more water until the
water finally begins to overflow. Draw the surface of the water just
before it began to overflow. Why do you think the water particles were
able to stay together for so long before spilling over the edge of the cup?
6. Tie the string to one end of the paper clip. Cover the paper clip with a
thin film of petroleum jelly. Hold the paper clip lengthwise with your
thumb and index finger, carefully place it on the edge of the cup. Use the
string to gently pull the paper clip off of the edge into the middle of the
cup. Why do you think the paper clip was able to float on the surface of
the water?
7. The skinlike property of the water’s surface, produced by the sticking
together of water particles, is called surface tension. Add one or two
drops of soap to the cup of water while the paper clip is still floating on
the surface. What happens?
8. How must the soap have changed the way in which the water’s surface
particles stick to one another?
9. Add 10 ml of water to each test tube. Add 2 drops of oil to one test tube, 2
drops of vinegar to the second test tube, 0.5 g of salt to the third test tube,
and 0.5 g of sugar to the last test tube. Gently mix the contents of each
test tube by covering the top with your thumb or with parafilm and
inverting several times. Record your observations below.
Conclusions
1. Some insects have the ability to walk, without sinking, on the top of pond
water. What must be true about these insects if this is possible?
2. Commercial laundries sometimes release their soapy waste water into
nearby ponds and streams. How could a study of water-walking insects
help to detect soap pollution?
3. On a rainy day, how can you identify a car that has been recently waxed
and polished?
Why do you think this happens?
4. Why should it be an advantage for plants to have leaves with shiny, waxy
upper surfaces when there is a heavy rain?