Water Cohesion and

Surface Tension

Take an Educated Prediction(Your hypothesis)

How many paper clips can you fit into the glass before the water runs over?

Actual Amount =

Let’s ExploreProcedureRub a few drops of cooking oil on your hand.

Let water from a faucet (tap) run over your hand then turn off the faucet. What happens?

Wash your hands with soap. Does this make the oil go away?

How it Works!!The water molecules stick together tightly and will

not mix with the oil on your hand. Since water molecules are attracted to each other so strongly, they formed small balls or drops which rolled over your oil coated hand. There is an invisible "skin" of surface tension around each drop.

Soap molecules are attracted to both water and oil. One end of the soap molecule sticks to oil, the other end sticks to water. The soap breaks up the surface tension and keeps the oil drops mixed in with the water so that the oil can wash off your hand.

Water

A drop of water is small, but it is made of even smaller parts called molecules

VocabularyCohesion- Water “sticks” to itself. Water molecules are attracted to each other.

Surface Tension- Water forms strong bonds on its surface. Its called a surface film or skin

SafetySafety Rules:• Never taste chemicals (or other substances)

used for a lab experiment.• Keep lids on all containers when not in use.• Clean up spills immediately.• Clean up your lab area and materials after

an experiment and return materials to their proper location.

Eyedroppers are not to be used as mini water guns!

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

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

Step 1: Rinse a penny in tap water and dry completely.

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.Step 4: Record the number of drops for that

trial in the table.

Part B: Perform tests with the TESTING LIQUID.Step 1: Start with a “clean” penny. Rinse the penny in tap water and

dry completely. Be sure to remove asmuch residue as possible - without using soap!Step 2: Hold the penny with the tweezers provided, then dip it into

the TESTING LIQUID. 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

WATER on the penny (one at a time) untilANY 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.Repeat Steps 1 - 4 three more times before calculating the average.