Lesson 10:
Properties of Water

 

Other Properties

Surface Tension


In a body of water, hydrogen bonds between water molecules are constantly pulling the molecules in many different directions.  However, at the water's surface, the molecules are only being pulled from side to side and down, with no hydrogen bonds pulling them upwards.  This results in a skin of water at the surface in which the molecules are held together very tightly. 

Surface tension
is a measurement of the amount of force required to break this skin on the surface of water.  Other liquids have a surface tension as well, but the surface tension in water is quite strong due to the hydrogen bonds.  The pictures below show some examples of the results of water's strong surface tension. 
 

Examples of surface tension.

Surface tension is what holds drops of water together in a round shape.  Surface tension allows both water striders and paperclips to float on water even though they are more dense than the water.  In addition, surface tension allows you to fill a cup slightly over the brim with water. 



Capillary Action

Surface tension is also responsible for another phenomena known as capillary action.  Capillary action occurs when water climbs upward through a small space, defying gravity due to the forces of adhesion and surface tension.  The image below shows one example of capillary action - a narrow straw was placed in a cup of water and the water crept upwards through the straw. 
Capillary action

What causes the movement of water during capillary action?  The first factor is adhesion, the attraction between water and another object.  In this case, adhesion attracted the water within the straw to the surface of the straw.  Molecules of water which came in contact with the straw tended to move upward along the inside of the straw, as shown below:

Adhesion pulls water up the sides of the straw

Water's surface tension is so strong that, as water is pulled upward along the straw's walls, the water in between tends to be pulled upward also.  The downward pull of gravity prevents the central water from rising quite as high as the water which is adhered to the straw, so the result is a meniscus, as shown in the first picture in this section. 

Capillary action is important in moving water upwards through small spaces.  Plants depend on capillary action to move water upward from the roots to the leaves.  In the soil, capillary action also tends to move water upward between the soil particles. 





Review

Water has many unique properties, many of which are based on its molecules' ability to form hydrogen bonds.  Water is found at earth's temperatures as a solid, liquid, and gas.  It has a high specific heat capacity and boiling point.  Water is most dense at 39°F.  Water also has a strong surface tension. 





Sources 

Byrd, Deborah, and Eleanor Imster.  "Moon's Day and Night."  Earth and Sky.  April 27, 2002. 

Chaplin, Mark.  2004.  "Water Structure and Behavior."  London South Bank University, London, England. 

Elert, Glenn, ed.  2002.  "Hottest Temperature on Earth." and "Coldest Temperature on Earth."  The Physics Factbook





Assignments

Complete the questions for Assignment 10, which deals with the properties of water explained in this lesson. When you have gotten all the answers correct, print the page and either mail or fax it to the instructor. You may also take the quiz online and directly submit it into the database for a grade.

 


Lab

There are no labs associated with this lesson.



Quiz

Answer the questions in the Quiz 10When you have gotten all the answers correct, print the page and either mail or fax it to the instructor.