What is the water?
Water (H 2 O) is the most abundant substance on earth, formed by hydrogen and oxygen molecules and commonly liquid. It is estimated that 71% of the earth’s surface is covered with water, although it is also frozen in the poles and mountain peaks (such as ice and snow) or in the form of gas (steam) in the atmosphere.
On our planet , water is kept in constant circulation thanks to the water cycle , a cycle of changes in physical state (liquid-gas-liquid) that allows the irrigation of land (rain) and the constant flow of rivers and seas. This cycle is known as the hydrological cycle, and it is vital for atmospheric cooling and climatic stability of the various regions.
Water is the liquid in which the originated life and the universal solvent, ie, which is to some degree in virtually all composite substances, in almost all chemical reactions of the planet.
Water is formed by two hydrogen atoms (H) and an oxygen atom (O) linked by covalent bonds, so that the molecule has a flat triangular shape. In other words, the hydrogen and oxygen atoms are separated from each other approximately 0.96 Angstroms (plus or minus one nanometer – one billionth of a meter) and the angle that their bond lines form is about 104.45 degrees.
In addition, water behaves like a dipole, that is, it has two regions with a certain electric charge. One of them is positive and the other negative.
The fact that water is a dipole is because hydrogen and oxygen are very different atoms from the point of view of electronegativity . This is an atomic property that indicates the way in which an atom attracts the electrons it shares with another in a covalent bond.
In the case of water, oxygen is a very electronegative atom. Hydrogen is a very little electronegative atom. The electrons that share in the two covalent bonds that the water molecule presents are “displaced” to the region occupied by oxygen. This implies that this zone has a little more (a differential) of negative charge, while hydrogens have positive charge differentials. We say that it has load differentials to highlight that water is NOT an electrically charged molecule, water IS NOT AN ION. Water, many others, is a polar molecule. This polarity is fundamental to understand the properties of water, why water behaves chemically as it does and by extension its importance within living beings.
Characteristics of water
The water does not have a certain flavor (or in any case a neutral flavor), so when ingested it will have the taste, in any case, of what is dissolved in it, such as water with sugar or salt.
Water does not have a certain color and lets the light rays pass almost completely, unless there are other substances dissolved in it and they do have a certain color, as occurs in waters rich in organic matter suspended from mangroves, That is cloudy.
In the same way that it does not taste, water also has no smell, except that which remains of those other substances dissolved in it.
Water is a good solvent of most substances (called hydrophilic) except for fats and lipids that do not dissolve or mix in it (hydrophobic). This is what happens when mixing water with oil: the substances remain separated.
Common water is a very good conductor of electricity, since electrically charged molecules (ions) are easily associated with it. That is why most salts are soluble in water. But if all kinds of minerals could be extracted from the water, the resulting liquid (pure water) would rather be an electrical insulator.
Water increases its conductivity if salts or other ionizing materials are added. Its unit is microsiemens per centimeter (?S / cm).
In a state of purity, water molecules behave diamagnetically, that is, they are repelled by intense magnetic fields.
In almost all conditions, water cannot be compressed, a principle used by hydraulic presses. It has a low viscosity (10 -3 Pas at about 20 ° C) and subjected to about 200 atmospheres, it is barely compressed at 1%.
The sound propagates in the water practically without loss, especially the low frequencies of the same. This property is what allows communication via Sonar, a principle copied from the communication of large marine cetaceans.
We can find water in three different states:
Changes in state occur when water passes from one state to another when heated or cooled.
– It goes to the solid state (ice) if it is at 0 ° or less
– It remains in a liquid state (water) between 0 ° and 100 °
– It goes into the gaseous state (water vapor) from 100 °
The main changes of state are: fusion, solidification, evaporation and condensation.
Like many other liquids, water presents a surface tension, a phenomenon in which the water molecules on the surface are attracted to the sides or down by intermolecular forces, offering a minimum surface resistance, as if it were a minimum elastic layer thickness.
This property is used by some insects that walk on the water, or explains why not all the leaves of the trees sink immediately after falling on the surface of a lake.
11. Melting point:
It is the temperature at which the solid and liquid phase coexist in equilibrium at 1 pressure atmosphere. For water, the melting point value is 0 ° C.
Its density is 1 g / cm 3 , that is, 1 cubic centimeter of liquid water weighs 1 gram; but when it is in a solid state (ice) its density is lower, so ice floats in liquid water. This phenomenon is called anomalous water dilation.
The maximum density of pure water is reached at 3.98 ° C and 1 atmosphere of pressure, and corresponds to 1 g / cm 3 .
Water density with temperature.
Density (g / cm 3 )
13. Specific heat
It is the amount of heat energy that is needed to raise the temperature of 1g of water by 1 ° C. The specific heat of water is 1 cal / g ° C.
14. Boiling point
It is the temperature at which the vapor pressure of a liquid is equal to the external atmospheric pressure. For water, the boiling point is 100 ° C.
The boiling point of a liquid depends on the external pressure. For example, at sea level, water boils at 100 ° C; however, if water is boiled on a mountain, the temperature at which it will boil will be lower.
Pure water is not colorless, it has a greenish blue tint in large volumes. The color aesthetically affects the potability of water and affects as a dye of certain products when used in its manufacture.
The color measurements are made by comparison with an arbitrary standard based on Cl2Co cobalt chloride and Cl6PtK2 potassium chloroplatin and is expressed on a scale of Pt-Co units (Hazen units) or simply Pt scale.
It is the difficulty of water to transmit light from suspended, colloidal or very fine materials. They are difficult materials to decant and filter.
The measurement is made by comparison with the turbidity induced by various substances. Devices called turbidimeters of which there are several types are used.
Color, turbidity and conductivity are used as parameters of water quality.