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5.3. Water properties

Water properties

Although you probably haven't started studying chemistry yet, you probably know that the formula for water is H2O. Water is made up of molecules made up of two hydrogen atoms (H) bonded to one oxygen atom (O). Although the electrical charge of each water molecule is neutral, it presents a dipolar structure, in such a way that it presents a somewhat negative charge in the zone of the oxygen atom, and a positive charge where the hydrogens are.

There is an attraction between these positive charges and other negative charges of other molecules and bonds called "hydrogen bonds" are produced. These bonds make the water in a liquid state at room temperature and not in a gaseous state as would be expected.

Water is colorless, odorless,  tasteless, incompressible, and in addition to these characteristics, we are going to deal with some of the properties of water due to its chemical structure:

Politicians and science:  Cristina Fernández de Kirchner, former president of Argentina, almost knows the formula for water .

Video: Properties of water (Amoeba sisters)

Water has thermoregulatory function

Water has a high specific heat. That is, it takes a lot of heat to increase its temperature, compared to other substances. It is capable of absorbing a lot of heat without hardly increasing its temperature. This is because the energy is used to break hydrogen bonds, not to increase the temperature by molecular agitation. Thus, it heats up and cools down more slowly than other liquids.

This property makes it have a thermoregulatory function, being a thermal stabilizer, keeping the body's temperature relatively constant, despite environmental fluctuations. For example, when we regulate our temperature with sweat.

In the same way, it also attenuates temperature variations, and the temperature of coastal areas are milder than those of inland areas. Its effect can also be seen in the sea ​​breezes that, during the day, the air that is on the continent warms up more, rises, and is occupied by the cooler air mass that is over the sea.

Water has a higher density in the liquid state than in the solid state

Normally, when we heat an object, it expands, and when we cool it, it contracts. But with water this does not happen. When the temperature drops, it freezes and expands.

The temperature at which water has the greatest density is 4°C. If the temperature drops, the water molecules are ordered and their volume increases, so their density decreases. This makes the ice (solid state) float on top of liquid water because it is less dense and there may be life below in aquatic ecosystems. The ice acts as a thermal insulator and prevents life from existing in the polar areas under water.

Water has great solvent power

Water, in addition to being very abundant on Earth, is the universal solvent, the one that can dissolve more substances. The polarity of its water molecules allows it to react with ions and electrically charged molecules, as well as other polar substances.

In nature we will not find pure water, H2O, but it is with a certain amount of salts in solution. Sea water still has a higher concentration of salts, with chlorine ions, sodium, calcium, magnesium, etc. Although not visible to the naked eye, salt becomes visible when the water in the salt pans evaporates.

The great solvent capacity of water allows it to perform two important functions:

  • Transport function: Water is the main means of transport for organisms (bloodraw and processed sap).
  • Metabolic and biochemical function: In the water, the biochemical reactions typical of life take place (which are carried out between molecules dissolved in water).

Water is a conductor of electricity

Although pure water is not a good conductor of electricity because it is neutral, in nature, water contains dissolved ions that make it a conductor of electricity. This allows electrical potentials to be created inside and outside the cells, necessary for muscle contraction, for example.

Although electricity can be very dangerous for living beings, it can also be used to revive the heart in case of cardiac arrest.

Water has high cohesive strength and adhesion

Water molecules have a strong attraction to each other and to other substances, which gives them some characteristic properties:

  • Water is highly incompressible.
  • Water has a structural function, it maintains the volume and shape of the cells.
  • Water has a high surface tension. It allows some organisms to move on the water without sinking.
  • The water rises by capillarity, so it can rise through the cracks, through the conductive vessels of the plants (sap).

Insecto zapatero posado sobre el agua

These properties and many others make water the most extraordinary substance in the world.

Experiment with some properties of water

  • Why do you think that part of the water we drink is used to produce sweat?
  • Why do the cubes melt when we put them in a glass of water?
  • Put a tablespoon of sugar or salt in a glass of water. Remove it and explain what happened.
  • Pour water into a glass and, being very careful not to spill over the edge, fill it as much as you can. Observe the surface of the water. Explain why the water is above the rim of the glass.
  • When we drink a drink with water and insert a straw into the glass, we can see that the level of the liquid inside the straw is above the level of the glass. Why?

Surface tension of water

Do you want to see a motorcycle running on water?