Since the electronegativity of the oxygen atom is higher than that of the hydrogen atom (2.1) according to the Pauling scale (3.5), the oxygen atom carries a partial negative charge; while the hydrogen atom carries a partial positive charge, water is therefore a polar molecule with a dipole moment of 1.84 Debye. Water can therefore form intermolecular hydrogen bonds. These factors lead to a strong intermolecular bonding force, which, in addition to the capillary property, explains the occurrence of the large surface tension of water. The surface tension of water explains the phenomenon that light insects can remain on the water surface and droplets can form, while the capillary property, which refers to the tendency of water to rise against gravity to the top of a thin capillary tube, is an important and vital property for vascular plants such as trees
Water is a good polar solvent and is often referred to as a "universal solvent." Water-soluble chemicals are hydrophilic substances such as salts, sugars, acids, alkalis, and some gases such as oxygen and carbon dioxide. Chemicals that are immiscible with water (such as fats (oils, greases, etc.)), on the other hand, are constant boiling (aziotropic mixture), but water does not mix with most organic oils because the latter form a lower density layer that floats on the water
surface
The value of the boiling point of water depends (as is the case for all liquids) on the value of the surrounding atmospheric pressure. For example, pure water boils at sea level at 100°C, while it boils at 68°C at the summit of Mount Everest (8,848m above sea level). When soluble substances are dissolved in water, the boiling point of water increases and its freezing point decreases.
The value of the specific heat capacity of water is 4181.3 J / (kg K), which is a relatively high value compared to other chemical compounds, and its heat of evaporation is also high (2257 kJ / kg). These high values are due to hydrogen bonds between water molecules. These high values contribute to making the Earth's climate moderate by absorbing large variations and fluctuations in temperature.
Water has a density of 1000 kg/m3 (equivalent to 1 g/mL) at 4°C, while ice has a density of 917 kg/m3. The density of water has a maximum value at 3.98 °C, after which it tends to decrease, unlike most other pure substances, whose density increases when its temperature decreases. The decrease in the density value is due to the open, non-compact structure of ice, which begins to form gradually in water with a low temperature (below 3.98 °C), as there is not enough thermal energy to secure the random movement directions of the molecules, which leads to their alignment at the molecular level, but with an open structure. regular, which leads to an increase in the general volume of the liquid; Therefore, between the two temperatures of 3.98 °C and 0 °C, the volume increases with the decrease in temperature. Water expands to occupy a volume greater than 9% of the volume of ice, so the density of ice will be less than the density of water, so ice floats on the surface of liquid water, as is the case in icebergs.
Pure water has a weak electrical conductivity, but it increases when a small amount of an ionic substance such as sodium chloride is dissolved.
When sufficient energy is applied to the water that exceeds the amount of standard heat of formation, which amounts to 285.8 kilojoules / mol (15.9 megajoules / kg), then the separation of the water molecule into its components of hydrogen and oxygen occurs, and this is what happens when a high voltage of electric current is applied under certain conditions to obtain the phenomenon of decomposition waterproof electrophoresis. The energy required to separate water into hydrogen and oxygen through electrolysis or other means exceeds the energy obtained from the interaction of the two mentioned elements. The electrolysis of water can be done at a tutorial level with a Hoffmann hydrolysis machine ;
2H2O=2H2+O2
Water is classified chemically as hydrogen oxide, which is formed when hydrogen or any compound containing it burns with oxygen, and it is an explosive mixture. Chemical elements more electronegative than hydrogen such as lithium, sodium, calcium, potassium, and cesium can displace hydrogen from water, forming corresponding hydroxides.
The water is described as hard when the percentage of mineral salts in the water is high, especially calcium (Ca+2) and magnesium (Mg+2) salts, in addition to some dissolved salts of bicarbonate and sulfate. On the other hand, non-hard water is described as “soft water”, and its definition varies according to the country, as it has a concentration of salts lower than 100 mg/l in the United Kingdom, and less than 60 mg/l in the United States of America. This feature is of importance in industry in particular, especially in boilers when evaporating, and it also has an impact on health, so it is usually subject to a softening process
A water detection reaction can be carried out by conventional inorganic methods, whereby water stains the white anhydrous copper sulfate salt to blue, and the paper impregnated with the anhydrous cobalt chloride salt turns from blue to red on contact with water. Analytically, the amount of water is determined using the Karl-Fischer method.
Acid Neutral: Water is a chemically neutral liquid, as its pH or alkaline level is 7, and this means that water cannot be considered an acidic or basic substance, because it is a chemically neutral substance.
According to the distribution and composition of hydrogen isotopes, in addition to the common “light” form, the water molecule can be in the form of heavy water when the hydrogen isotope is deuterium in the first place in the water molecule (D2O), and it can also be in the form of superheavy water when tritium replaces the hydrogen in water molecule (T2O).
Basic uses :
1- household uses:
Irrigation is the most important water use in agriculture and is essential for food production. Water withdrawals for crop irrigation can account for up to 90% of total withdrawals in some developing countries, and even in developed countries the percentage of water withdrawals for irrigation reaches a significant percentage, such as in the United States of America, where the percentage of freshwater withdrawals for irrigation is about 30%.
The importance of awareness of the rational use of water resources has increased in recent decades, especially with the increase in the number of people on the planet and their need for water for drinking and irrigation for food, which has necessitated the development of methods such as drip irrigation. Urban sprawl and increasing water demand in other sectors, such as alternative energy production (biofuels), have led to talk of peak water. Water demand is expected to increase even more in the future than it does today to ensure sufficient food supplies as the world's population increases, estimated to reach 9 billion people by 2050.
In 2007, an agricultural water management assessment was conducted by the International Water Management Institute in Sri Lanka to determine whether the world has enough water to feed the growing global population. The assessment process was based on the availability of water resources in that year that can be used in agriculture around the world, and it specifically presented locations that suffer from water scarcity, as it was determined that one-fifth of the world's population, or more than 1.2 billion people, live in areas that suffer from material scarcity. For water, where there is not enough water to meet all necessary needs. It also found that 1.6 billion people worldwide live in areas of economic water scarcity, as lack of investment and weak economies make it impossible for government agencies in these areas to meet the demand for water. The report concluded that continuing the current pace of food production and the use of irrigation water to grow crops will eventually lead to crises in many regions of the world, and that this can be avoided if farmers increase their efficiency and productivity by reducing waste as much as possible through rationalization and the use of modern irrigation methods.
2- Industry :
Water is of great importance in industry and has many applications. Water is mainly used as a coolant and medium in heat exchangers because it is abundant and has a high heat capacity, whether for cooling or heating. Cold water can be obtained from available natural sources such as a flowing river, a nearby lake or from the sea. Heating water for heat transfer is an effective process in which the water evaporates and condenses due to its high evaporating temperature. However, one of the disadvantages of using steam is the corrosion of metallic materials used in industry, such as steel and copper, when untreated water is used. In all cogeneration plants, water is used as a fluid to transfer heat in a closed loop between the boiler, turbines and condenser. It is also used as a heat conductor in cooling towers. In nuclear power plants and reactors, water is used simultaneously as a neutron moderator and as a coolant.
In the chemical industry, water has many important applications in the form of solvents or chemical reagents. It is also used in various chemical processes as a reaction medium in general and, in particular, for cleaning and rinsing (usually with detergents or alkaline solutions), for dissolving, for extraction and for recrystallization. Water is also used as a medium for electrolysis and electroplating, as well as for the production of batteries.
In various technical processes, water is used as a medium for binding and forming gypsum and cement, as well as for splitting, cutting and cleaning under high pressure, and as a pressure transmission medium in some hydraulic applications.
Water energy is used to generate electricity in the form of hydropower, which is the power generated by water when it drives turbines connected to an electricity generator. Hydropower is one of the clean renewable energy sources, usually obtained through the construction of dams on rivers.
3- Trade and transportation:
The crossing of waters is used for the transportation of goods and travel. In the past, voyages by ship for research and trade purposes were an important means of crossing the great distances between the seas. Nowadays, travel is limited by large ships for tourist purposes, while most shipping traffic currently serves commercial purposes. Some waterways are characterized by a strategic location that gives them great commercial importance, such as the Suez Canal and the Panama Canal.
Currently, the use of water as a commodity is included, as in some areas commercial rights to springs and streams containing fresh mineral or groundwater are acquired and bottled in glass or plastic bottles and sold in the form of bottled water, which may sometimes be carbonated (sparkling). The use of bottled water is most common in countries suffering from a shortage of natural freshwater resources, which has led to the spread of the concept of "water privatization."
With the scarcity of water resources and the compulsion of developing countries to export agricultural products that require freshwater for irrigation, the concept of virtual water, which indicates the amount of water used to produce a particular agricultural crop, emerged. For example, an average of 1,600 cubic meters of water is needed to produce one ton of wheat. This concept highlights the need to know the choice of the type of agricultural crops and to classify them into those that should be grown and exported and those that should be imported.
1 Comments
THANK
ReplyDeletePost a Comment
If you like the encyclopedia platform, do not forget to leave us a nice comment