Theme: Water around us

This paper is the result of five students' comprehensive practical activities. This paper expounds the composition and properties of water, classifies and compares the water in our life, and on this basis, expounds their respective uses. Finally, the water pollution situation and its causes in Zhenjiang section of the Yangtze River basin and the ancient canal basin are analyzed, and the control ideas are put forward preliminarily.

Keywords: water, around water, classification, use, water pollution

Water (H2O) is an inorganic substance composed of hydrogen and oxygen, and it is a colorless and odorless transparent liquid at normal temperature and pressure. Water is one of the most common substances, an important resource for all life, including human beings, and the most important component of organisms. Water plays an important role in the evolution of life.

1 properties of water

1. 1 Physical properties Water is a colorless and odorless transparent liquid at normal temperature and pressure. At 20℃, the thermal conductivity of water is 0.006 J/s? 6? 1cm？ 6? 1K, and the thermal conductivity of ice is 0.023 J/s? 6? 1cm？ 6? 1K, when the density of snow is 0. 1× 103 kg/m3, the thermal conductivity of snow is 0.00029 J/s? 6? 1cm？ 6? 1K at 3.98℃, the maximum density of water is 1× 103kg/m3. When the temperature is higher than 3.98℃, the density of water decreases with the increase of temperature. At 0 ~ 3.98℃, water does not obey the law of thermal expansion and cold contraction, but its density increases with the increase of temperature. At 0℃, the density of water is 0.99987× 103 kg/m3, and the density of ice is 0.9 167× 103 kg/m3. Water is a good solvent, and most inorganic compounds and a few organic compounds are soluble in water.

1.2 chemical properties

1.2. 1 thermal stability of water. Water has strong thermal stability. When water vapor is heated above 2000K, only a small amount will be decomposed into hydrogen and oxygen, but water will be decomposed into hydrogen and oxygen when charged.

2H2O 2H2↑ + O2↑

1.2.2 water reacts with metals. Many active metals can react with water, such as sodium, potassium and iron.

2Na + 2H2O = H2 ↑+ 2NaOH

3Fe + 4H2O Fe3O4 + 4H2

1.2.3 water reacts with nonmetals. A few nonmetals can react with water, such as fluorine gas, chlorine gas and carbon.

Cl2 +H2O HCl + HClO

1.2.4 water and some metal oxides and nonmetallic oxides can react with water. Such as sodium oxide, calcium oxide, carbon dioxide, sulfur dioxide, etc.

Na2O + H2O = 2NaOH

SO2 + H2O H2SO3

1.2.5 reacts with other substances.

NH3 + H2O NH3。 H2O

Calcium chloride+H2O → calcium hydroxide+acetylene

2 Classification of water and its application

2. 1 Ordinary water, heavy water and ultra-heavy water

There are three kinds of nuclides of hydrogen, namely ordinary hydrogen (nucleus 1 proton, also called deuterium), heavy hydrogen (nucleus 1 proton and 1 neutron, also called deuterium) and overweight hydrogen (nucleus 1 proton and 2 neutron, also called tritium). The molecular formula of ordinary water is H2O. Heavy water is also called deuterium oxide or deuterium water, and its molecular formula is D2O. Heavy water is a colorless, odorless and tasteless liquid, but its physical properties are slightly different from ordinary water. For example, the density of heavy water is 1. 1044g/cm3(25℃), while that of ordinary water is 0.9970 1g/cm3(25℃). This is the origin of the name heavy water. The melting point of heavy water is 3.8 1℃, and the boiling point is 10 1.42℃. The solubility of salt in heavy water is less than that in ordinary water. For example, at 25℃, 100g ordinary water can dissolve 35.92gNaCl, while 100g heavy water can only dissolve 30.56gNaCl. Many substances react with heavy water more slowly than ordinary water. Heavy water has an adverse effect on living things. Plant seeds can't germinate when soaked in heavy water, and fish will die quickly in heavy water. Ordinary water contains about 0.0 15% heavy water. When water is electrolyzed, the release speed of common hydrogen (H2) is 6 times faster than that of specific hydrogen (D2), so the heavy water in electrolyzed water residue is enriched. At present, the methods of producing heavy water include electrolysis, rectification and chemical exchange. Heavy water is mainly used as moderator (also called moderator) and coolant in reactors. Deuterium produced during the decomposition of heavy water is an important thermonuclear fuel. In chemistry and biology, heavy water is used as a tracer to study the reaction mechanism. The chemical molecular formula of super heavy water is T2O, and each heavy water molecule consists of two tritium atoms and one oxygen atom. Ultra-heavy water is extremely rare in natural water, and its proportion is less than one billion. The production cost of ultra-heavy water is tens of thousands of times higher than that of water.

2.2 Water in life

2.2. 1 tap water is natural water after filtration, precipitation and disinfection. The main component is water, followed by some ions such as Ca2+, Mg2+ and Cl-. Although the tap water has been treated, there are still traces of bacteria such as Escherichia coli and some other solutes, so the tap water cannot be directly drunk. Tap water is denser than pure water and has no fixed boiling point. Tap water can be drunk after being heated and boiled, and can be directly used as industrial water.

2.2.2 Mineral water Mineral water is unpolluted underground mineral water that naturally gushes out from deep underground or is exposed artificially. Mineral water contains many minerals and trace elements beneficial to human body, such as lithium, strontium, selenium, zinc, bromine and molybdenum. , has a strong physiological function and has a certain health care effect on the human body. In general, the chemical composition, flow rate and water temperature of mineral water are relatively stable within the natural fluctuation range.

2.2.3 Pure water Pure water is made from rivers, lakes and tap water. Through distillation, electrodialysis, ion exchange and reverse osmosis. Sterile purity is achieved through complicated deep purification procedures. Pure water removes all kinds of elements in water to the maximum extent, leaving only water molecules. While removing harmful substances, it also removes beneficial substances, so you can't drink pure water for a long time, but drink it with mineral water.

2.2.4 magnetized water magnetized water is a kind of water obtained by magnetizing water with high-tech superconducting magnets and changing the structure of water molecules. After water is magnetized, its physical and chemical properties have changed greatly, mainly in the increase of conductivity, PH value, density, volatility, dissolved oxygen (DO) and insoluble solubility. Under most magnetic fields, the surface tension of magnetized water increases and the boiling point decreases. Under a few magnetic fields, the surface tension decreases and the boiling point increases. The freezing point of magnetized water has little change. Magnetized water has many uses in production and life because of its different structure and properties from ordinary water. Medically, it has certain stimulation and curative effect on diseases such as hypertension, diabetes, thick blood and kidney calculi. Drinking magnetized water also has a certain effect on eliminating exercise fatigue. The application of magnetized water in industry has the functions of scale prevention, scale prevention, dust removal and improving the strength of concrete. Irrigating crops with magnetized water in agriculture can activate various biological enzymes, enhance the biological activity of enzymes, promote the formation of chlorophyll and improve photosynthesis, thus promoting the growth and development of crops and improving the yield and quality of crops. Using magnetized water to raise fish can enhance the growth, disease resistance and cold resistance of fish.

2.2.5 Superwater heats and evaporates ordinary water into steam in a closed container, and makes the steam condense in a timely capillary (the inner diameter is in the order of nm). The water thus obtained is called super water, and some people call it nano water unscientifically. After treatment, the super-water association structure changed greatly, and a chain-like hexagonal ring structure polymer was formed, and its particle size reached the order of nm. Because of the particularity of super-water structure, it has some properties different from ordinary water: ① its density is 1.4 times that of ordinary water (ρ chao =1.4 ρ pu); ② Its viscosity coefficient is 15 times higher than that of ordinary water (η Chao = 15η Pu) and its volatility is low; ③ The freezing point of super water is-100℃, and it still maintains its characteristics at 700℃. When heated to 900~ 1000℃, it becomes common water, and its characteristics will not change whether it is heated, cooled or stored for a long time at-100~700℃. Superwater has high activity and can easily enter between molecules of other substances. Some substances incompatible with ordinary water, such as fuel oil, can be well dissolved with super water, and water enters between oil molecules, which changes the interaction between molecules and makes the molecular structure more loose. Fuel oil containing a certain proportion of super water has low ignition point and full combustion. On the one hand, it can improve the combustion rate and mechanical efficiency, on the other hand, it can reduce air pollution, which has great economic and social benefits. Using super water as solvent, it can be made into liquid solution at low temperature. According to its low volatility and high viscosity coefficient, it can also be made into volatile and impermeable solution, which is of great use in industry.

2.2.6 Reclaimed water refers to high-quality miscellaneous drainage (excluding feces and kitchen drainage), miscellaneous drainage (excluding feces and sewage) and domestic sewage (wastewater) used by people in life and production, which can reach a certain water quality standard and can be reused in a certain range, and its water quality is between the upper water (clear water) and the lower water (sewage). There are many explanations for "reclaimed water". It is called "reclaimed water" in sewage engineering, "circulating water" or "reclaimed water" in factories, and some people call it "reclaimed water". Generally, water quality is used as a distinguishing sign. The treated reclaimed water quality must meet the following conditions: (1) It meets the hygiene requirements: its indicators mainly include coliform bacteria, total bacteria, residual chlorine, suspended solids, COD, BOD5, etc. (2) Satisfy people's sensory requirements, without unpleasant feelings, and its measurement indicators include turbidity, chromaticity, smell, etc. (3) Meet the requirements of equipment structure, that is, the water quality is not easy to cause serious corrosion and scaling of equipment and pipelines, and its measurement indicators include PH value, hardness, evaporation residue, dissolved substances, etc. The treated wastewater is generally used for flushing toilets, spraying roads, greening, car washing and as supplementary water for cooling water.

2.3 Hard water and soft water

2.3. 1 Soft water contains little or no calcium ions and magnesium ions. Generally, water with hardness below 8 degrees is soft water.

2.3.2 Hard water contains more calcium ions and magnesium ions. Generally, water with hardness higher than 8 degrees is hard water. Hard water will affect the effect of detergent, and heating with hard water will have more scale. Generally speaking, hard water should be softened before it is used in industry.

2.4 Fresh water and salt water

2.4. 1 Fresh water with little or no salt is generally used as domestic water or industrial water.

2.4.2 Salt water contains more salt, such as salt lake water in the north, and some groundwater and seawater are salt water.