Chemistry
Water in Chemical Reactions
Water plays a crucial role in chemical reactions as a solvent, reactant, or product. It can act as a medium for reactions to occur, participate in hydrolysis reactions, and contribute to acid-base chemistry. Additionally, water's ability to dissolve a wide range of substances makes it essential for many chemical processes.
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11 Key excerpts on "Water in Chemical Reactions"
eBook - ePub- Gene E. Likens(Author)
- 2010(Publication Date)
- Academic Press(Publisher)
Properties of Water
Passage contains an image Chemical Properties of Water
J.H. Aldstadt, III; H.A. Bootsma University of Wisconsin-Milwaukee, Milwaukee, WI, USAJ.L. Ammerman SEAL Analytical, Inc., Mequon Technology Center, Mequon, WI, USAWater is H2 O, hydrogen two parts, oxygen one, but there is also a third thing, that makes it water and nobody knows what it is.—D.H. Lawrence (1929)Introduction
Water is the most abundant molecule on Earth. In spite of being so common, water is quite unusual – from its high melting and boiling points to its tremendous solvating power, high surface tension, and the largest dielectric constant of any liquid. In this article, we present an overview of the chemical properties of water. The phrase ‘chemical property’ is context dependent, which we define in general as a description of the way that a substance changes its identity in the formation of other substances. A universally accepted set of chemical properties does not exist in the same way that there is, more or less, a standard set of physical properties for a given substance. Whereas a given substance has intrinsic physical properties (such as melting point), by our definition chemical properties are clearly tied to change. In addition to reactivity, a substance’s ‘chemical properties’ also typically include its electronegativity, ionization potential, preferred oxidation state(s), coordination behavior, and the types of bonding (e.g., ionic, covalent) in which it participates. Because these properties are extensively studied in general chemistry courses, we will not further discuss them here. Rather, we move beyond the basic general chemistry concepts and focus upon water in a limnologic context – particularly, its bulk fluid structure and aspects of its chemical reactivity in the hydrosphere.In the following pages, we begin by briefly reviewing the molecular structure of water and then discuss models for its structure in ‘bulk’ solution. We then turn our attention to the hydration of ions and an overview of important reactions that involve water, including acid–base, complexation, precipitation, and electron transfer. We conclude with a look at trends in the chemical composition of freshwater that are fundamental to the field of limnology.
eBook - PDFReaction Rate Constant Computations
Theories and Applications
- Keli Han, Tianshu Chu(Authors)
- 2013(Publication Date)
- Royal Society of Chemistry(Publisher)
The application areas outlined above require an understanding of the role of water under conditions ranging from near ambient, which are of interest for biology, biochemistry and medicine, to near critical and supercritical, import-ant for green chemistry technologies and nuclear power engineering. In the first part of this chapter we provide an overview of the physical and solvent properties of water that may influence the mechanism and kinetics of radical reactions. In many applications the role of hydrogen bonding is often ignored because of experimental difficulties in characterising the aqueous so-lution on a microscopic level. Computational tools are less limited. Com-parative molecular simulations have proved to be useful for the generation of a comprehensive view of solvent structure and dynamics depending on the con-ditions of temperature and pressure. In the second part of this chapter the methodology used in simulations to analyse hydrogen bonding is presented. Then we demonstrate how insight into the hydrogen bonding may improve our understanding of the free radical behaviour, providing a guide for experiment and modelling kinetics of radical reactions in water. In the last part we focus on the Noyes relationship and its application to the assessment of rate constants at temperatures that are important for green chemistry technologies and nuclear power engineering. Use of the Noyes equation is advantageous because one can explicitly model solvent effects on diffusion and chemical transformation of reactants. We conclude with a reference to reactions involving water as a reactant. These reactions may significantly affect the chemistry of aqueous systems at high temperatures. Role of Water in Radical Reactions: Molecular Simulation and Modelling 353 15.2 Physical and Solvent Properties of Water The physical and solvent properties of water depend strongly on temperature and pressure.
eBook - ePubThe Science of Water
Concepts and Applications
- Frank R. Spellman(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
3 . The formula shows that this compound is made up of three elements: sodium, carbon, and oxygen. In addition, there are two atoms of sodium, one atom of carbon, and three atoms of oxygen in each molecule.As mentioned, when depicting chemical reactions, chemical equations are used. The following equation shows a chemical reaction that most water/wastewater operators are familiar with: Chlorine gas added to water. It shows the formulas of the molecules that react together and the formulas of the product molecules.+Cl2H 2O → HOCl + HClAs stated previously, a chemical equation tells what elements and compounds are present before and after a chemical reaction. Sulfuric acid poured over zinc will cause the release of hydrogen and the formation of zinc sulfate. This is shown by the following equation:Zn +H 2→SO4+ZnSO4H 2One atom (also one molecule) of zinc unites with one molecule of sulfuric acid and gives one molecule of zinc sulfate and one molecule (two atoms) of hydrogen. Notice that there is the same number of atoms of each element on each side of the arrow. However, the atoms are combined differently.Let us look at another example. When hydrogen gas is burned in air, the oxygen from the air unites with the hydrogen and forms water. The water is the product of burning hydrogen. This can be expressed as an equation:
This equation indicates that two molecules of hydrogen unite with one molecule of oxygen to form two molecules of water.+2H2→O2O2H2Water Solutions
A solution is a condition in which one or more substances are uniformly and evenly mixed or dissolved. A solution has two components: a solvent and a solute. The solvent is the component that does the dissolving. The solute is the component that is dissolved. In water solutions, water is the solvent. Water can dissolve many other substances—given enough time, there are not too many solids, liquids, and gases that water cannot dissolve. When water dissolves substances, it creates solutions with many impurities.Generally, a solution is usually transparent and not cloudy. However, a solution may be colored when the solute remains uniformly distributed throughout the solution and does not settle with time.
eBook - PDFWater in Biological and Chemical Processes
From Structure and Dynamics to Function
- Biman Bagchi(Author)
- 2013(Publication Date)
- Cambridge University Press(Publisher)
7 An essential chemical for life processes: water in biological functions Water molecules play diverse roles in facilitating biological processes that are aided by their unique features mentioned in Chapter 1. The dynamic and spatial heterogeneity in the hydration shell of proteins facilitates many important processes, such as enzyme functions, molecu- lar recognition, and protein association, to name a few. Water plays another role in facilitating drug–DNA intercalation, as discussed below. While some of these actions have been discussed extensively in the literature, the direct participation of water molecules where one of the oxygen–hydrogen bonds is broken and the resulting proton and hydroxyl anion are used as chemicals seems to have escaped much articulation, even though these steps can influence the kinetics of the catalysis pro- cesses profoundly. In fact this is really impressive chemistry because, as we discussed in Chapter 4, the breaking of the oxygen–hydrogen covalent bond to create a hydroxyl anion and a proton is a rare process in bulk water, but this occurs apparently in an effortless manner in enzyme catalysis. We cannot stop without mentioning its inevitable role in photo- synthesis. In this chapter we try to congregate a few specific examples where water plays a role as a direct collaborator in the functioning of the biological world. 7.1 Introduction We all know that water controls chemical and physical changes in the biological world in both direct and indirect fashions. This was recognized long ago by Leonardo da Vinci, who termed water a “vehicle of natural changes”. It is also termed, albeit less poetically, a “lubricant of life”. What, however, was probably not recognized earlier is that water actively and directly participates in (that is, not just mediates or lubricates) a large number of biological processes, making their occurrence possible in the first place.
eBook - PDFSoil and Water Chemistry
An Integrative Approach, Second Edition
- Michael E. Essington(Author)
- 2015(Publication Date)
- CRC Press(Publisher)
207 5 Soil Water Chemistry Soil water, or the aqueous phase, is arguably the most important phase in the soil. Almost all chemi-cal reactions in the soil are mediated by or occur in the soil solution. Some of the more important types of chemical reactions that occur in soil water, affecting the fate and behavior of substances in the environment, are hydration–hydrolysis, acid–base, oxidation–reduction, and complexation. The soil solution mediates many of the reactions that control the retention of substances by soil solids, such as precipitation–dissolution, adsorption–desorption, and ion exchange. The extent to which these mobility- and retention-controlling reactions occur is dictated by substance behavior in soil water. The soil solution is also the principal phase in which substances move in and through the soil. It is for these reasons that considerable emphasis is placed on understanding the processes that occur in the soil solution, as well as the ability to predict how these processes will impact substance fate and behavior. 5.1 NATURE OF WATER Water is a highly reactive substance and an exceedingly effective solvent. It is a compound that has a high dielectric constant , which is a measure of a solvent’s ability to overcome the attraction between a dissolved cation and an anion. The dielectric constant may also be defined as the ability to oppose the electrical attraction between ions of opposite charge. This definition is illustrated mathemati-cally in the expression F Z Z r = uni239B uni239D uni239C uni239E uni23A0 uni239F uni239B uni239D uni239C uni239E uni23A0 uni239F + -ε 2 1 (5.1) where F is the force of attraction between ions of opposite charge of magnitude Z – and Z + that are separated by a radius of r in a solution having a dielectric constant of ε . The force of attraction between two oppositely charged ions will be less in solvents that have high dielectric constants, relative to solvents that have low dielectric constants.
- Shu Kobayashi(Author)
- 2014(Publication Date)
- Thieme Chemistry(Publisher)
The main limitation that has prevented a more widespread industrial use of water as a solvent for organic reactions is the poor solubility of many organic reactants. However, the same property makes water a suitable solvent for biphasic catalysis, where the substrates and products constitute the organic phase and water contains the catalyst (see, for example, Section 7.1). This setup ensures facile separation between catalyst and products. The re- cently discovered special effects related to “on water” reactions (see Section 2.8.5) further expands the scope of water as a green solvent for chemical reactions. 2.9 Epilogue Water may be a tiny molecule, but it has a huge impact on life and on chemistry. Water harbors a large collection of anomalous properties that are the source of lasting amaze- ment and wonder. Through the efforts of many scientists, water is slowly revealing its se- crets and our understanding of water and the processes occurring therein is continuously improving. Partly building on these developments, the interest in water as a reaction me- dium is increasing. However, despite its reputation as an environmentally benign solvent, the use of water as a medium for organic chemistry is still not as widespread as it could be. The high reactivity of water constitutes a major limitation. In addition, the poor solubility of nonpolar molecules is often a reason for many synthetic chemists to avoid water. Yet the same poor solubility may also be an advantage, accelerating reactions that lead to a reduction of hydrophobic surface area during the activation process. Furthermore, under heterogeneous conditions, “on water” reactions may be accelerated, most likely as a result of activation through hydrogen bonding at the interface between the organic phase and water. For both types of water-promoted reactions the scope is not yet fully charted and many opportunities for further development exist.
eBook - ePubGreen Solvents, Volume 5
Reactions in Water
- Paul T. Anastas(Author)
- 2014(Publication Date)
- Wiley-VCH(Publisher)
1 The Principles of and Reasons for Using Water as a Solvent for Green Chemistry Ronald Breslow1.1 Introduction
Chemical reactions used to manufacture important compounds such as medicinals are essentially always carried out in solution, and this is also true of the research work that is used to invent the new compounds and to develop appropriate ways to manufacture them. In the past, continuing into the present, the solvents used are normally volatile organic compounds (VOCs), and these pose an environmental problem. Their vapors can contribute to the greenhouse effect that causes global warming, and in some cases the solvent vapors can catalyze the destruction of the ozone layer that protects the Earth and its living inhabitants from short-wavelength ultraviolet solar radiation. The vapors may also be toxic to humans, plants, or animals, or they may cause diseases.The liquids themselves can be a problem. If they are released into the earth, rivers or the ocean, they can cause direct environmental damage, while also slowly releasing their vapors. In principle, the solvents can be completely captured and purified for reuse during manufacturing, but it is difficult to prevent some loss to the environment. Hence there is interest in using environmentally benign liquids as the solvents in chemical reactions.One possibility is supercritical carbon dioxide, which is a liquid under pressure and which has attractive solvent properties. However, unless it is completely contained and reused, it will release gaseous carbon dioxide, a greenhouse gas. Thus interest has increasingly turned to water as the solvent for chemical reactions.Water is the solvent in which biochemical reactions are performed in Nature, and it is environmentally benign. However, it is a good solvent only for organic chemicals that have polar groups, such as alcohols and carboxylic acids. This may not be an insuperable problem. Over 20 years ago we reported that the special selectivities seen in water solution (see below) were also seen in some water suspensions, where one soluble component reacted with one that was poorly soluble [1, 2]. We pointed out that such suspensions in water could well be generally more practical ways to use water in manufacturing [2]. Recently, Sharpless and co-workers described a remarkable acceleration of a reaction in such a suspension, which they called reactions ON water [3, 4]. The large reported rate effect was seen in only one particular case, but even without a large acceleration the selectivities that we describe below could perhaps make suspensions in water a practical way for the environmentally benign properties of water to be generally useful even with insoluble reaction components.
eBook - ePubNatural Water Remediation
Chemistry and Technology
- James G. Speight(Author)
- 2019(Publication Date)
- Butterworth-Heinemann(Publisher)
Rapaport, 1983 ). In liquid water there is much disorder, but the attractive forces between molecules are strongly evident. The energy required to separate the molecules is indicated by the high heat of vaporization of water, and in another way by its high surface tension. Liquid water has some of the properties of a polymer. The presence of dissolved ions in water changes some of its physical properties, notably its ability to conduct electricity. The dipolar nature of the water molecule, however, is an important factor in the behavior of the solute ions as well as the solvent.The dipolar water molecules are strongly attracted to most mineral surfaces, form sheaths arranged in an orderly pattern around many forms of dissolved ions, and insulate the electrical charges on the ions from other charged species. The effectiveness of water as a solvent is related to such activities. Its effectiveness in weathering rocks is also increased by the ability of this cohesive liquid to wet mineral surfaces and penetrate into small openings.2 The hydrosphere
The hydrosphere (often referred to as the aquasphere) is generally defined by geochemists as the vapor, liquid, and solid water present at and near the land surface, and its dissolved constituents. Water vapor and condensed water of the atmosphere are usually included, but water that is immobilized by incorporation into mineral structures in rocks is usually not thought of as part of the hydrosphere. In fact, in the processes of the hydrological cycle on the Earth, connecting hydrosphere with atmosphere, lithosphere and biosphere (Fig. 3.2 ) the chemical composition of water is formed. Interacting with all the components of the natural landscape and being influenced by natural and man-made factors, water, a universal solvent, is enriched by a wide variety of different substances in gaseous, solid and liquid states that create an enormous variability of natural water types from the perspective of their chemical composition.Fig. 3.2
eBook - PDFEnvironmental Science and Technology
A Sustainable Approach to Green Science and Technology, Second Edition
- Stanley E. Manahan(Author)
- 2006(Publication Date)
- CRC Press(Publisher)
water is the ultimate green chemical compound. Although the chemical formula of water is simple and the H Although the chemical formula of water is simple and the H 2 O molecule is O molecule is small, the behavior of this unique substance is unusual and complex. The special small, the behavior of this unique substance is unusual and complex. The special properties of water are because of its molecular structure and the interaction of properties of water are because of its molecular structure and the interaction of water molecules with each other. These aspects of water are discussed along with its water molecules with each other. These aspects of water are discussed along with its chemical properties in Chapter 5. But at this point, several things need to be empha-chemical properties in Chapter 5. But at this point, several things need to be empha-sized regarding the water molecule. The formation of the water molecule from atoms sized regarding the water molecule. The formation of the water molecule from atoms of hydrogen and oxygen were shown in Figure 3.6. Rather than showing the water of hydrogen and oxygen were shown in Figure 3.6. Rather than showing the water molecule as a linear structure of H–O–H, it was illustrated with the two H atoms molecule as a linear structure of H–O–H, it was illustrated with the two H atoms forming an angle on the same “side” of the O atom. The reason for this structure forming an angle on the same “side” of the O atom. The reason for this structure is that the outer shell of eight electrons in the O atom of H is that the outer shell of eight electrons in the O atom of H 2 O is composed of four O is composed of four pairs of electrons, two pairs of which are in the covalent bonds between the H and O pairs of electrons, two pairs of which are in the covalent bonds between the H and O atoms and two pairs of which are not involved in bonds. It turns out that such pairs atoms and two pairs of which are not involved in bonds.
eBook - ePubWater Is ...
The Indispensability of Water in Society and Life
- Seth B Darling, Seth W Snyder(Authors)
- 2018(Publication Date)
- WSPC(Publisher)
In addition to all of these extraordinary physical properties of water that result in large part from its polarity, water’s polar nature also makes it a phenomenally effective solvent. That is, water is capable of dissolving a breathtaking variety of different substances; it is, in fact, often called the “universal solvent.” Those materials that are attracted to water (and therefore are likely to dissolve well) are anthropomorphically called “hydrophilic” (water-loving) and those that are not are called “hydrophobic” (water-fearing). When ionic or polar molecules such as acids, salts, sugars, or alcohols encounter water, many water molecules surround them with the negatively charged oxygen sides of water attracting the positively charged components of the solute and the positively charged hydrogen sides attracting the negative components. Dissolved molecules are therefore said to be “hydrated” by a shell of water molecules. It is even possible to get small amounts of some non-polar substances such as carbon dioxide or gasoline to dissolve in water via a process where water either induces mild polarity in the solute or there is a gain in entropy (greater dispersal of the solute molecules relative to the pure materials) from the dissolution process. Since the Big Bang, nature strives to increase entropy. Water’s unique ability to dissolve so many different substances is critical for life. Our bodies, like those of all living things, contain many thousands of different chemicals — each solvated in water. Wherever water goes, whether through the soil and rocks, through our bodies, or through the atmosphere, it grabs other substances and takes them along for the ride. Such action carries valuable minerals and nutrients to sustain life and reshape the world around us, but it has an unfortunate flip side — water is also extremely easy to pollute.Let’s take a look at some examples of the universal solvent in action and its central importance. One of the non-polar substances that can dissolve in water, although only in relatively low concentrations (just a few milligrams per liter), is oxygen (O2
eBook - PDF- Fatih Yildiz(Author)
- 2009(Publication Date)
- CRC Press(Publisher)
While there is ongoing research to achieve improvements in the methods of water analysis [19,20], recent interest is also forwarded to the economic aspects of water determination in foodstuffs [21]. 1.3 WATER AS A SOLVENT Water is a good solvent for most biomolecules, which are generally charged or polar compounds. The form and function of biomolecules in an aqueous environment are governed by the chemistry of Direct methods Indirect methods Determination of water in foods Physical methods Dessication to achieve an equilibrium Distillation Oven drying Infrared, halogen, and microwave drying Chemical methods Combined methods Calcium carbide and calcium hydride methods Karl fischer titration Evaporation and Karl Fischer titration Evaporation and diphosphorus pentoxide method Densimetry, polarimetry, refractometry, and electrical property measurements Use of water activity tables NMR spectroscopy NIR spectroscopy MW spectroscopy FIGURE 1.1 Methods for determining water content of foods. (Based on Isengard, H.-D., Food Control , 12, 395, 2001.) 6 Advances in Food Biochemistry their component atoms and the effect of water molecules surrounding them. The polar and cohesive properties of water are especially of importance for its solvent characteristics. The introduction of any substance to water results in altered properties for the substance and water itself. The degree and type of alteration is dependent on the molecular and electronic struc-ture, ionization characteristics, size, and stereochemistry of the solute. The substance introduced into water, depending on these properties, will be dissolved, dispersed, or suspended. Water dissolves small molecules such as salts, sugars, or water-soluble vitamins to form “true solutions” which may either be ionic or molecular. When different chemical and biochemical materials are introduced into water, there is a rise in the boiling point and viscosity and a decrease in the freezing point and surface tension.
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