DOCSLIB.ORG

Solute - Solvent

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Solute - Solvent Unit 7.3 Solutions: Solute - Solvent Is snow an aqueous solution? In the winter, the temperature often gets well below the freezing point of water. This condition can create problem in car radiators. If the water freezes, water hoses will break, the engine block can crack, and significant damage can be done to the car. Solute and Solvent When one substance dissolves into another, a solution is formed. A solution is a homogeneous mixture consisting of a solute dissolved into a solvent. The solute is the substance that is being dissolved, while the solvent is the dissolving medium. Solutions can be formed with many different types and forms of solutes and solvents. Types of Solutions Type Solvent Solute Example gas/gas nitrogen oxygen air liquid/gas water carbon dioxide soda pop liquid/liquid water ethylene glycol antifreeze liquid/solid water salts seawater solid/solid iron carbon and chromium stainless steel (alloys) Gas Solutions Our air is a homogeneous mixture of many different gases and therefore qualifies as a solution. Approximately 78% of the atmosphere is nitrogen, making it the solvent for this solution. The next major constituent is oxygen (about 21%), followed by the inert gas argon (0.9%), carbon dioxide (0.04%) and trace amounts of neon, methane, helium, and other gases. Solid-Solid Solutions Solid-solid solutions such as brass, bronze, and sterling silver are called alloys. Bronze (composed mainly of copper with added tin) was widely used in making weapons in times past dating back to at least 2400 B.C. This metal alloy was hard and tough, but was eventually replaced by iron. A turkey timer is an example of an alloy in use. The timer has a plastic casing, B, along with a plastic plunger, A. There is a spring, C, that will push the plunger up, when the turkey reaches the appropriate temperature. In the tip, is a solid solution alloy, D. The alloy holds the plunger down until the turkey reaches the “done” temperature, approximately 165 o F. At that temperature, the alloy melts allowing the spring to push the plunger up., signaling that the turkey is fully cooked. Liquid-Solid Solutions Perhaps the most familiar liquid-solid solution is dental amalgam, used to fill teeth when there is a cavity. Approximately 50% of the amalgam material is liquid mercury to which a powdered alloy of silver, tin and copper is added. Mercury is used because it binds well with the solid metal alloy. However, the use of mercury-based dental amalgam has gone under question in recent years because of concerns regarding the toxicity of mercury. Many filling are now out of a composite resin, which do not contain mercury. We want to focus on solutions where the solvent is water. An aqueous solution is water that contains one or more dissolved substances. The dissolved substances in an aqueous solution may be solids, gases, or other liquids. Examples include vinegar (acetic acid in water), alcoholic beverages (ethanol in water), and liquid cough medicines (various drugs in water). In order to be a true solution, a mixture must be stable. When sugar is fully dissolved into water, it can stand for an indefinite amount of time and the sugar will not settle out of the solution. Further, if the sugar-water solution is passed through a filter it will be unchanged. The dissolved sugar particles will pass through the filter along with the water. This is because the dissolved particles in a solution are very small, usually less than 1 nm in diameter. Solute particles can be atoms, ions, or molecules, depending on the type of substance that has been dissolved. How do you make sure a compound is pure? Solutions are often used to purify compounds. When compounds are synthesized, they often have contaminating materials mixed in with them. The process of recrystallization can be used to remove these impurities. The crystals are dissolved in a hot solvent, forming a solution. When the solvent is cooled the compound is no longer as soluble and will precipitate out of solution, leaving other materials still dissolved. Saturated and Unsaturated Solutions Table salt (NaCl) readily dissolves in water. Suppose that you have a beaker of water to which you add some salt, stirring until it dissolves. So you add more and that dissolves. You keep adding more and more salt, eventually reaching a point that no more of the salt will dissolve no matter how long or how vigorously you stir it. Why? On the molecular level, we know that action of the water causes the individual ions to break apart from the salt crystal and enter the solution, where they remain hydrated (surrounded) by water molecules. What also happens is that some of the dissolved ions collide back again with the crystal and remain there. Recrystallization is the process of dissolved solute returning to the solid state. At some point the rate at which the solid salt is dissolving becomes equal to the rate at which the dissolved solute is recrystallizing. When that point is reached, the total amount of dissolved salt remains unchanged. Solution equilibrium is the physical state described by the opposing processes of dissolution and recrystallization occurring at the same rate. The solution equilibrium for the dissolving of sodium chloride can be represented by one of two equations. NaCl (s) NaCl (aq) While this shows the change of state back and forth between solid and aqueous solution, the preferred equation also shows the dissociation that occurs as an ionic solid dissolves. +1 -1 NaCl (s) Na (aq) + Cl (aq) When the solution equilibrium point is reached and no more solute will dissolve, the solution is said to be saturated. A saturated solution is a solution that contains the maximum amount of solute that is capable of being dissolved. At 20°C, the maximum amount of NaCl that will dissolve in 100 mL of water is 36.0 g of NaCl. If any more NaCl is added past that point, it will not dissolve because the solution is saturated. What if more water is added to the solution instead? Now more NaCl would be capable of dissolving in the additional solvent. An unsaturated solution is a solution that contains less than the maximum amount of solute that is capable of being dissolved. When 30.0 grams of NaCl is added to 100 mL of water, it all dissolves, forming an unsaturated solution. When 40.0 grams is added, 36.0 grams dissolves and 4.0 grams remains undissolved, forming a saturated solution. How can you tell if a solution is saturated or unsaturated? If more solute is added and it does not dissolve, then the original solution was saturated. If the added solute dissolves, then the original solution was unsaturated. A solution that has been allowed to reach equilibrium but which has extra undissolved solute at the bottom of the container must be saturated. How does a hot or a cold pack work? In the picture, a thermal pack is applied to the back. Small packs can be used either for heating or cooling, depending on the material used. A heat pack contains a supersaturated solution of material such as sodium acetate. The solution is clear until a small metal trigger is activated. The sodium acetate then crystallizes out of solution and generates heat in the process. Supersaturated Solutions Some solutes, such as sodium acetate, do not recrystallize easily. Suppose an exactly saturated solution of sodium acetate is prepared at 50°C. As it cools back to room temperature, no crystals appear in the solution, even though the solubility of sodium acetate is lower at room temperature. A supersaturated solution is a solution that contains more than the maximum amount of solute that is capable of being dissolved at a given temperature. The recrystallization of the excess dissolved solute in a supersaturated solution can be initiated by the addition of a tiny crystal of solute, called a seed crystal. The seed crystal provides a nucleation site on which the excess dissolved crystals can begin to grow. Recrystallization from a supersaturated solution is typically very fast. Rock candy is often made this way. Summary A solution is a homogeneous mixture of a solute in a solvent. A solute is the material present in the smaller amount in the solution. It is being dissolved. A solvent is the material present in the larger amount in the solution. It is doing the dissolving. Saturated solutions contain the maximum amount of solute that can be dissolved. Unsaturated solutions contain less than the maximum amount of solute that can be dissolved. Supersaturated solutions contain more than the maximum amount of solute that can be dissolved. This is done by heating the solution. A supersaturated solution can recyrstallize when a seed crystal is added to the solution. Review 1. What is a solution? 2. What is the solute? 3. What is the solvent? 4. Why is nitrogen the solvent in air? 5. Why is the preferred equation for solution equilibrium of NaCl an equilibrium between solid NaCl and ions? 6. What will happen if a saturated solution of NaCl that also contains solid NaCl, has more water added? 7. How do we know a solution is supersaturated? Answers 1. A solution is a homogeneous mixture consisting of a solute dissolved into a solvent. 2. The substance in the smaller amount in the solution. It is the substance that is dissolved. There can be more than one solute. 3. The substance in the greatest amount in the solution. It is the substance that does the dissolving. 4. Nitrogen is in the greatest amount in the air.
Load more

Recommended publications
  • Homework 5 Solutions
    SCI 1410: materials science & solid state chemistry HOMEWORK 5. solutions Textbook Problems: Imperfections in Solids 1. Askeland 4-67. Why is most “gold” or “silver” jewelry made out of gold or silver alloyed with copper, i.e, what advantages does copper offer? We have two major considerations in jewelry alloying: strength and cost. Copper additions obviously lower the cost of gold or silver (Note that 14K gold is actually only about 50% gold). Copper and other alloy additions also strengthen pure gold and pure silver. In both gold and silver, copper will strengthen the material by either solid solution strengthening (substitutional Cu atoms in the Au or Ag crystal), or by formation of second phase in the microstructure. 2. Solid state solubility. Of the elements in the chart below, name those that would form each of the following relationships with copper (non-metals only have atomic radii listed): a. Substitutional solid solution with complete solubility o Ni and possibly Ag, Pd, and Pt b. Substitutional solid solution of incomplete solubility o Ag, Pd, and Pt (if you didn’t include these in part (a); Al, Co, Cr, Fe, Zn c. An interstitial solid solution o C, H, O (small atomic radii) Element Atomic Radius (nm) Crystal Structure Electronegativity Valence Cu 0.1278 FCC 1.9 +2 C 0.071 H 0.046 O 0.060 Ag 0.1445 FCC 1.9 +1 Al 0.1431 FCC 1.5 +3 Co 0.1253 HCP 1.8 +2 Cr 0.1249 BCC 1.6 +3 Fe 0.1241 BCC 1.8 +2 Ni 0.1246 FCC 1.8 +2 Pd 0.1376 FCC 2.2 +2 Pt 0.1387 FCC 2.2 +2 Zn 0.1332 HCP 1.6 +2 3.
    [Show full text]
  • Chapter 15: Solutions
    452-487_Ch15-866418 5/10/06 10:51 AM Page 452 CHAPTER 15 Solutions Chemistry 6.b, 6.c, 6.d, 6.e, 7.b I&E 1.a, 1.b, 1.c, 1.d, 1.j, 1.m What You’ll Learn ▲ You will describe and cate- gorize solutions. ▲ You will calculate concen- trations of solutions. ▲ You will analyze the colliga- tive properties of solutions. ▲ You will compare and con- trast heterogeneous mixtures. Why It’s Important The air you breathe, the fluids in your body, and some of the foods you ingest are solu- tions. Because solutions are so common, learning about their behavior is fundamental to understanding chemistry. Visit the Chemistry Web site at chemistrymc.com to find links about solutions. Though it isn’t apparent, there are at least three different solu- tions in this photo; the air, the lake in the foreground, and the steel used in the construction of the buildings are all solutions. 452 Chapter 15 452-487_Ch15-866418 5/10/06 10:52 AM Page 453 DISCOVERY LAB Solution Formation Chemistry 6.b, 7.b I&E 1.d he intermolecular forces among dissolving particles and the Tattractive forces between solute and solvent particles result in an overall energy change. Can this change be observed? Safety Precautions Dispose of solutions by flushing them down a drain with excess water. Procedure 1. Measure 10 g of ammonium chloride (NH4Cl) and place it in a Materials 100-mL beaker. balance 2. Add 30 mL of water to the NH4Cl, stirring with your stirring rod.
    [Show full text]
  • Self-Assembly of a Colloidal Interstitial Solid Solution with Tunable Sublattice Doping: Supplementary Information
    Self-assembly of a colloidal interstitial solid solution with tunable sublattice doping: Supplementary information L. Filion,∗ M. Hermes, R. Ni, E. C. M. Vermolen,† A. Kuijk, C. G. Christova,‡ J. C. P. Stiefelhagen, T. Vissers, A. van Blaaderen, and M. Dijkstra Soft Condensed Matter, Debye Institute for NanoMaterials Science, Utrecht University, Princetonplein 1, NL-3584 CC Utrecht, the Netherlands I. CRYSTAL STRUCTURE LS6 In the main paper we use full free-energy calculations to determine the phase diagram for binary mixtures of hard spheres with size ratio σS/σL = 0.3 where σS(L) is the diameter of the small (large) particles. The phases we considered included a structure with LS6 stoichiometry for which we could not identify an atomic analogue. Snapshots of this structure from various perspectives are shown in Fig. S1. FIG. S1: Unit cell of the binary LS6 superlattice structure described in this paper. Note that both species exhibit long-range crystalline order. The unit cell is based on a body-centered-cubic cell of the large particles in contrast to the face-centered-cubic cell associated with the interstitial solid solution covering most of the phase diagram (Fig. 1). II. PHASE DIAGRAM AT CONSTANT VOLUME 3 In the main paper, we present the xS − p representation of the phase diagram where p = βPσL is the reduced pressure, xS = NS/(NS + NL), NS(L) is the number of small (large) hard spheres, β = 1/kBT , kB is the Boltzmann constant, and T is the absolute temperature. This is the natural representation arising from common tangent construc- tions at constant pressure and the representation required for further simulation studies such as nucleation studies.
    [Show full text]
  • Solid Solution Softening and Enhanced Ductility in Concentrated FCC Silver Solid Solution Alloys
    UC Irvine UC Irvine Previously Published Works Title Solid solution softening and enhanced ductility in concentrated FCC silver solid solution alloys Permalink https://escholarship.org/uc/item/7d05p55k Authors Huo, Yongjun Wu, Jiaqi Lee, Chin C Publication Date 2018-06-27 DOI 10.1016/j.msea.2018.05.057 Peer reviewed eScholarship.org Powered by the California Digital Library University of California Materials Science & Engineering A 729 (2018) 208–218 Contents lists available at ScienceDirect Materials Science & Engineering A journal homepage: www.elsevier.com/locate/msea Solid solution softening and enhanced ductility in concentrated FCC silver T solid solution alloys ⁎ Yongjun Huoa,b, , Jiaqi Wua,b, Chin C. Leea,b a Electrical Engineering and Computer Science University of California, Irvine, CA 92697-2660, United States b Materials and Manufacturing Technology University of California, Irvine, CA 92697-2660, United States ARTICLE INFO ABSTRACT Keywords: The major adoptions of silver-based bonding wires and silver-sintering methods in the electronic packaging Concentrated solid solutions industry have incited the fundamental material properties research on the silver-based alloys. Recently, an Solid solution softening abnormal phenomenon, namely, solid solution softening, was observed in stress vs. strain characterization of Ag- Twinning-induced plasticity In solid solution. In this paper, the mechanical properties of additional concentrated silver solid solution phases Localized homologous temperature with other solute elements, Al, Ga and Sn, have been experimentally determined, with their work hardening Advanced joining materials behaviors and the corresponding fractography further analyzed. Particularly, the concentrated Ag-Ga solid so- lution has been discovered to possess the best combination of mechanical properties, namely, lowest yield strength, highest ductility and highest strength, among the concentrated solid solutions of the current study.
    [Show full text]
  • 101 Lime Solvent
    Sure Klean® CLEANING & PROTECTIVE TREATMENTS 101 Lime Solvent Sure Klean® 101 Lime Solvent is a concentrated acidic cleaner for dark-colored brick and tile REGULATORY COMPLIANCE surfaces which are not subject to metallic oxidation. VOC Compliance Safely removes excess mortar and construction dirt. Sure Klean® 101 Lime Solvent is compliant with all national, state and district VOC regulations. ADVANTAGES • Removes construction dirt and excess mortar with TYPICAL TECHNICAL DATA simple cold water rinse. Clear, brown liquid • Removes efflorescence from new brick and new FORM Pungent odor stone construction. SPECIFIC GRAVITY 1.12 • Safer than muriatic acid on colored mortar and dark-colored new masonry surfaces. pH 0.50 @ 1:6 dilution • Proven effective since 1954. WT/GAL 9.39 lbs Limitations ACTIVE CONTENT not applicable • Not generally effective in removal of atmospheric TOTAL SOLIDS not applicable stains and black carbon found on older masonry VOC CONTENT not applicable surfaces. Use the appropriate Sure Klean® FLASH POINT not applicable restoration cleaner to remove atmospheric staining from older masonry surfaces. FREEZE POINT <–22° F (<–30° C) • Not for use on polished natural stone. SHELF LIFE 3 years in tightly sealed, • Not for use on treated low-E glass; acrylic and unopened container polycarbonate sheet glazing; and glazing with surface-applied reflective, metallic or other synthetic coatings and films. SAFETY INFORMATION Always read full label and SDS for precautionary instructions before use. Use appropriate safety equipment and job site controls during application and handling. 24-Hour Emergency Information: INFOTRAC at 800-535-5053 Product Data Sheet • Page 1 of 4 • Item #10010 – 102715 • ©2015 PROSOCO, Inc.
    [Show full text]
  • Solvent Effects on the Thermodynamic Functions of Dissociation of Anilines and Phenols
    University of Wollongong Research Online University of Wollongong Thesis Collection 1954-2016 University of Wollongong Thesis Collections 1982 Solvent effects on the thermodynamic functions of dissociation of anilines and phenols Barkat A. Khawaja University of Wollongong Follow this and additional works at: https://ro.uow.edu.au/theses University of Wollongong Copyright Warning You may print or download ONE copy of this document for the purpose of your own research or study. The University does not authorise you to copy, communicate or otherwise make available electronically to any other person any copyright material contained on this site. You are reminded of the following: This work is copyright. Apart from any use permitted under the Copyright Act 1968, no part of this work may be reproduced by any process, nor may any other exclusive right be exercised, without the permission of the author. Copyright owners are entitled to take legal action against persons who infringe their copyright. A reproduction of material that is protected by copyright may be a copyright infringement. A court may impose penalties and award damages in relation to offences and infringements relating to copyright material. Higher penalties may apply, and higher damages may be awarded, for offences and infringements involving the conversion of material into digital or electronic form. Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong. Recommended Citation Khawaja, Barkat A., Solvent effects on the thermodynamic functions of dissociation of anilines and phenols, Master of Science thesis, Department of Chemistry, University of Wollongong, 1982.
    [Show full text]
  • Solvent-Tunable Binding of Hydrophilic and Hydrophobic Guests by Amphiphilic Molecular Baskets Yan Zhao Iowa State University, [email protected]
    Chemistry Publications Chemistry 8-2005 Solvent-Tunable Binding of Hydrophilic and Hydrophobic Guests by Amphiphilic Molecular Baskets Yan Zhao Iowa State University, [email protected] Eui-Hyun Ryu Iowa State University Follow this and additional works at: http://lib.dr.iastate.edu/chem_pubs Part of the Chemistry Commons The ompc lete bibliographic information for this item can be found at http://lib.dr.iastate.edu/ chem_pubs/197. For information on how to cite this item, please visit http://lib.dr.iastate.edu/ howtocite.html. This Article is brought to you for free and open access by the Chemistry at Iowa State University Digital Repository. It has been accepted for inclusion in Chemistry Publications by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Solvent-Tunable Binding of Hydrophilic and Hydrophobic Guests by Amphiphilic Molecular Baskets Abstract Responsive amphiphilic molecular baskets were obtained by attaching four facially amphiphilic cholate groups to a tetraaminocalixarene scaffold. Their binding properties can be switched by solvent changes. In nonpolar solvents, the molecules utilize the hydrophilic faces of the cholates to bind hydrophilic molecules such as glucose derivatives. In polar solvents, the molecules employ the hydrophobic faces of the cholates to bind hydrophobic guests. A water-soluble basket can bind polycyclic aromatic hydrocarbons including anthracene, pyrene, and perylene. The binding free energy (−ΔG) ranges from 5 to 8 kcal/mol and is directly proportional to the surface area of the aromatic hosts. Binding of both hydrophilic and hydrophobic guests is driven by solvophobic interactions. Disciplines Chemistry Comments Reprinted (adapted) with permission from Journal of Organic Chemistry 70 (2005): 7585, doi:10.1021/ jo051127f.
    [Show full text]
  • I. the Nature of Solutions
    Solutions The Nature of Solutions Definitions Solution - homogeneous mixture Solute - substance being dissolved Solvent - present in greater amount Types of Solutions SOLUTE – the part of a Solute Solvent Example solution that is being dissolved (usually the solid solid ? lesser amount) solid liquid ? SOLVENT – the part of a solution that gas solid ? dissolves the solute (usually the greater liquid liquid ? amount) gas liquid ? Solute + Solvent = Solution gas gas ? Is it a Solution? Homogeneous Mixture (Solution) Tyndall no Effect? Solution Is it a Solution? Solution • homogeneous • very small particles • no Tyndall effect • particles don’t settle • Ex: •rubbing alcohol Is it a Solution? Homogeneous Mixture (Solution) Tyndall no Effect? yes Solution Suspension, Colloid, or Emulsion Will mixture separate if allowed to stand? no Colloid (very fine solid in liquid) Is it a Solution? Colloid • homogeneous • very fine particles • Tyndall effect • particles don’t settle • Ex: •milk Is it a Solution? Homogeneous Mixture (Solution) Tyndall Effect? no yes Solution Suspension, Colloid, or Emulsion Will mixture separate if allowed to stand? no yes Colloid Suspension or Emulsion Solid or liquid particles? solid Suspension (course solid in liquid) Is it a Solution? Suspension • homogeneous • large particles • Tyndall effect • particles settle if given enough time • Ex: • Pepto-Bismol • Fresh-squeezed lemonade Is it a Solution? Homogeneous Mixture (Solution) Tyndall no Effect? yes Solution Suspension, Colloid, or Emulsion Will mixture separate if allowed to stand? no yes Colloid Suspension or Emulsion Solid or liquid particles? solid liquid Suspension (course solid in liquid) Emulsion (liquid in liquid) Is it a Solution? Emulsion • homogeneous • mixture of two immiscible liquids • Tyndall effect • particles settle if given enough time • Ex: • Mayonnaise Pure Substances vs.
    [Show full text]
  • Chapter 18 Solutions and Their Behavior
    Chapter 18 Solutions and Their Behavior 18.1 Properties of Solutions Lesson Objectives The student will: • define a solution. • describe the composition of solutions. • define the terms solute and solvent. • identify the solute and solvent in a solution. • describe the different types of solutions and give examples of each type. • define colloids and suspensions. • explain the differences among solutions, colloids, and suspensions. • list some common examples of colloids. Vocabulary • colloid • solute • solution • solvent • suspension • Tyndall effect Introduction In this chapter, we begin our study of solution chemistry. We all might think that we know what a solution is, listing a drink like tea or soda as an example of a solution. What you might not have realized, however, is that the air or alloys such as brass are all classified as solutions. Why are these classified as solutions? Why wouldn’t milk be classified as a true solution? To answer these questions, we have to learn some specific properties of solutions. Let’s begin with the definition of a solution and look at some of the different types of solutions. www.ck12.org 394 E-Book Page 402 Homogeneous Mixtures A solution is a homogeneous mixture of substances (the prefix “homo-” means “same”), meaning that the properties are the same throughout the solution. Take, for example, the vinegar that is used in cooking. Vinegar is approximately 5% acetic acid in water. This means that every teaspoon of vinegar contains 5% acetic acid and 95% water. When a solution is said to have uniform properties, the definition is referring to properties at the particle level.
    [Show full text]
  • Chapter 4 Solution Theory
    SMA5101 Thermodynamics of Materials Ceder 2001 Chapter 4 Solution Theory In the first chapters we dealt primarily with closed systems for which only heat and work is transferred between the system and the environment. In the this chapter, we study the thermodynamics of systems that can also exchange matter with other systems or with the environment, and in particular, systems with more than one component. First we focus on homogeneous systems called solutions. Next we consider heterogeneous systems with emphasis on the equilibrium between different multi-component phases. 4.1 WHAT IS A SOLUTION? A solution in thermodynamics refers to a system with more than one chemical component that is mixed homogeneously at the molecular level. A well-known example of a solution is salt water: The Na+, Cl- and H2O ions are intimately mixed at the atomic level. Many systems can be characterized as a dispersion of one phase within another phase. Although such systems typically contain more than one chemical component, they do not form a solution. Solutions are not limited to liquids: for example air, a mixture of predominantly N2 and O2, forms a vapor solution. Solid solutions such as the solid phase in the Si-Ge system are also common. Figure 4.1. schematically illustrates a binary solid solution and a binary liquid solution at the atomic level. Figure 4.1: (a) The (111) plane of the fcc lattice showing a cut of a binary A-B solid solution whereby A atoms (empty circles) are uniformly mixed with B atoms (filled circles) on the atomic level.
    [Show full text]
  • Solid-Liquid Partition Coefficients, Rcjs: What's the Value and When Does It Matter?
    Radioprotection - Colloques, volume 37, Cl (2002) Cl-225 Solid-liquid partition coefficients, rCjs: What's the value and when does it matter? M.I. Sheppard and S.C. Sheppard ECOMatters, 24 Aberdeen Avenue, P.O. Box 430, Pinawa, Manitoba ROE 1L0, Canada Abstract. Environmental risk assessments binge on our ability to predict the fete and mobility of radionuclides and metals in terrestrial soils and aquatic sediments. Solid-solution partitioning (the Kd approach), despite its shortcomings, has been used extensively. Much attention has been devoted to grooming the existing key compendia for values applicable for each nuclear risk assessment carried out worldwide. This appears to be an important task. For example, soil Kd values for a single nuclide can vary over several orders of magnitude, yet the soil Kd value is the most important parameter in the soil leaching model. Similarly, plant uptake depends primarily on the nuclide present in solution phase. Despite this apparent sensitivity, our experience has shown that risk assessors dwell too much on the precision of the Kd value for all nuclides. This paper discusses the effect of the Kd value on the resulting soil concentration during leaching and identifies those radionuclides and assessment conditions where a precise value is required. Only those radionuclides that typically have a soil Kd value of 10 LAg or less (Tc, CL I, As) need be accurately described for timeframes of up to 10,000 years for desired soil model prediction outcomes (soil concentrations within two-fold). 1. INTRODUCTION Environmental risk assessments of radionuclides and metals are key to acceptance and sustainability of industrial progress and the disposal of industry's wastes, particularly in the nuclear and imriing and metal smelting industry.
    [Show full text]
  • Chemical Equilibrium and Reaction Modeling of Arsenic and Selenium in Soils
    3 Chemical Equilibrium and Reaction Modeling of Arsenic and Selenium in Soils Sabine Goldberg CONTENTS Inorganic Chemistry of As and Se in Soil Solution .......................................... 66 Methylation and Volatilization Reactions ......................................................... 66 Precipitation-Dissolution Reactions .................................................................. 68 Oxidation-Reduction Reactions .......................................................................... 68 Adsorption-Desorption Reactions ..................................................................... 69 Modeling of Adsorption by Soils: Empirical Models ...................................... 70 Modeling of Adsorption by Soils: Constant Capacitance ModeL................ 72 Summary................................................................................................................ 86 References ............................................................................................................... 87 High concentrations of the trace elements arsenic (As) and selenium (Se) in soils pose a threat to agricultural production and the health of humans and animals. As is toxic to both plants and animals. Se, despite being an essential micronutrient for animal nutrition, is potentially toxic because the concentra­ tion range between deficiency and toxicity in animals is narrow. Seleniferous soils release enough Se to produce vegetation toxic to grazing animals. Such soils occur in the semiarid states of the western United
    [Show full text]