Chemistry

Water cycles


After the earth formed, its surface cooled, clouds and rain formed. From the rains the rivers, lakes, seas, oceans and groundwater formed.

Clouds form by evaporating liquid water, which always returns to Earth in the form of rain, snow or hail. Then it evaporates again and thus forms the water cycle.

The larger the water exposure surface, the higher the evaporation level. Water vapor, when cooled, can also form the fog (fog), that is, that "cloud" that forms near the ground. Soil water is absorbed by plant roots. Through perspiration, plants eliminate water in the vapor state to the environment, especially through the leaves.

And in the food chain, plants, through fruits, roots, seeds and leaves, transfer water to their consumers. In addition to what is ingested by food, animals obtain water by drinking it directly. They return water to the environment by sweating, breathing, and eliminating urine and feces. This water evaporates and returns to the atmosphere. On our planet, the water cycle is permanent.

In this cycle, rain is crucial not only for its return to Earth, but also for its distribution in different parts of the planet. It redistributes all the moisture of the earth. It does not always come clean, as during its evaporation. Depending on where it falls, sometimes rainwater can become contaminated, especially in polluted cities. Even so, it can be reused by most plants and animals. On average, each water molecule goes through this cycle every ten to fifteen days. There are molecules that remain in the oceans for over 1500 years.

Component separation

In nature, it is very difficult to find pure water. The water that covers our planet is largely in the oceans and seas. We call this type of water saltwater because it contains a large amount of salts dissolved in it, such as sodium chloride (NaCl) or table salt. But there are also rivers, streams, lakes and groundwater, which we call freshwater, this name is due to the presence of a small amount of dissolved salt and not because the water is really sweet.

How to separate components from water?

Water is made up of two hydrogen atoms and one oxygen. We can use the voltmeter to separate these components.

This device is made of 3 or 4 large batteries connected in series, a bottle of water, some lemon juice, two test tubes filled with this mixture and two pieces of electrical cord. Lemon juice helps in the passage of electric current. When this current begins to circulate bubbles form in the tubes. These bubbles are hydrogen gas and oxygen gas, which are invisible gases and therefore difficult to identify.

The tube that contains the smallest volume of water is the one with hydrogen gas, since the formula of water is always two atoms of H to one of O. so hydrogen is double. This process of separating the components of a substance through the electric current is called electrolysis, in this case, electrolysis of water.

How to test these gases?

The gases involved in the experiment (hydrogen and oxygen) have different properties. So it's easier to check which gas is in each pipe.

Hydrogen gas is combustible and therefore can be burned. If we remove the tube we believe to be hydrogen and put a lit matchstick, there should be a small explosion. So in this tube is the hydrogen gas.

Oxygen gas is oxidizing, that is, it causes combustion (burning). If this procedure is done on the tube that may contain oxygen, we should note that the ember will be “revived” by rekindling the toothpick. So in this tube contains oxygen.

As we have seen, pure water is hardly found in nature. This water contains only H molecules.2O. Usually we find water with dissolved salts, gases and impurities.

Potable water: is the appropriate drinking water. It must be crystal clear, ie colorless and clear; odorless (odorless) and tasteless (tasteless); free of impurities (microbes and toxic substances). It may contain some dissolved salts and gases in small quantities. Some impurities can be removed with the aid of a household filter.

Mineral water: is water that contains dissolved mineral salts. They are beneficial to the human being. This water can be classified according to the minerals that compose it. In Brazil, there are many sources of mineral water, called Hydromineral Resorts.

- sulphurous water - Aguas de São Pedro (SP), Araxá and Poços de Caldas (MG), Dorizon (PR).
- bicarbonated water - Águas de Prata (SP) and Salutaris (RJ).
- chlorinated water - Caldas do Cipó (BA).
- carbogasous and ferruginous water - Lambari, Caxumbu and São Lourenço (MG).
- bicarbonate-chlorinated water - Iraí (RS).

Thermal water: is water that contains minerals and comes out of the soil at high temperature (geyser). In Brazil, there are also several sources of thermal water, such as in Goiás, where the water temperature can reach 40 ° C. The thermal water bath is very good for health.

Distilled water: is water obtained by distillation, which is a homogeneous mixture separation method, ie it contains only one phase.