Purpose: To observe and explain several unique properties of water: cohesion, adhesion, and surface tension.
Materials: Water, beaker, pipette (dropper), penny, paper towels.
1.Place the penny on the paper towel. Using the pipette, carefully place drops of water on the penny. Observe carefully as you add water.
2.Count the number of drops until the “bubble” bursts. Record the number of drops in a clearly labeled chart.
3.Perform three trials (Repeat steps 1& 2 three times).
4.Calculate the average number of drops from your 3 trials. Record the data in your chart.
Drops of Water:
Trial 1 74
Trial 2 61
Trial 3 56
Conclusions: Water molecules are able to bond to one another in clusters on account of their polar nature; that is why so many drops of water could reside on the single penny. The oxygen in water has a negative charge, while the hydrogen in water carries a positive charge. The hydrogen atoms in water molecules are naturally attracted to the oxygen in other water molecules. This natural pull is what attributes water with its cohesive and adhesive properties.
coherence: the state of cohering or sticking together
surface tension: the contracting force per unit length around the perimeter of a surface is usually referred to as surface tension if the surface separates gas from liquid or solid phases, and interfacial tension if the surface separates two nongaseous phases. Surface tension can also be expressed in units of energy per unit surface area. For practical purposes surface tension is frequently taken to reflect the change in surface free energy per unit increase in surface area.
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