Properties of Water
Water covers about three fourths of the surface of the earth? It is ubiquitous. It is also one of the simplest yet most important molecules in living systems. It makes up from 50 to 95 percent of the weight of living organisms. The cytoplasm of a cell is a water-based solution that contains a variety of ions, salts, and molecules which make life ‘happen.’ Water is literally involved in every facet of life.
The simplicity of the water molecule belies the complexity of its properties. Based on its small size and light weight, one can predict how it should behave, yet it remains liquid at a much higher temperatures than expected. It also boils and freezes at much too high, or low, of a temperature for a molecule of its size. Many of these unexpected properties of water are due to the fact that water molecules are attracted to each other like small magnets (cohesion). This attraction results in turn from the structure of the water molecule and the characteristics of the atoms it contains.
Each molecule of water is made up of two atoms of hydrogen connected to one atom of oxygen, as shown below. This summarized in the familiar formula, H2O.
Figure 3. Formation of a Water Molecule
Hydrogen in water will take on a partial positive charge and why oxygen will take on a partial negative charge. This causes a water molecule to be polar, having opposite + and – charges on each end of the molecule. These partial charges cause water molecules to ‘stick’ to each other like magnets. The ‘stickiness’ in this particular case is due to ‘hydrogen bonding‘. In this case, hydrogen bonding involves the attraction between the positively charged hydrogen atom of one water molecule and the negatively charged oxygen atom of another water molecule. As no electrons are actually shared however, hydrogen bonds are much weaker than covalent bonds – they easily break and easily form again.
Water is everywhere. It’s in the air we breathe. It’s in our sink faucets, and it’s in every cell of our body. Water is an unusual substance with special properties. The properties of water help to answer several questions such as:
In this first lab, we will investigate the properties of water in an attempt to understand how water behaves in relation to both our bodies and the environment. Through a set of experiments, the unique properties of water and its consequent importance to living things will become apparent.
chromatography paper strips
|Once you have completed this exercise you should be able to:|
|1.||Describe the polarity of a water molecule and explain how that polarity affects the properties of water.|
|2.||Explain why water climbs the inside of a thin glass capillary but not a thin plastic capillary.|
|3.||Explain why water climbs a paper strip.|