DOCSLIB.ORG

Dissociation Mechanisms of Dissolved Alkali Silicates in Sodium Hydroxide

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Dissociation Mechanisms of Dissolved Alkali Silicates in Sodium Hydroxide Dissociation Mechanisms of Dissolved Alkali Silicates in Sodium Hydroxide The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. Citation Dupuis, Romain et al. "Dissociation Mechanisms of Dissolved Alkali Silicates in Sodium Hydroxide." Journal of Physical Chemistry C 124, 15 (March 2020): 8288–8294 © 2020 American Chemical Society As Published http://dx.doi.org/10.1021/acs.jpcc.0c01495 Publisher American Chemical Society (ACS) Version Final published version Citable link https://hdl.handle.net/1721.1/129405 Terms of Use Creative Commons Attribution 4.0 International license Detailed Terms https://creativecommons.org/licenses/by/4.0/ This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited. pubs.acs.org/JPCC Article Dissociation Mechanisms of Dissolved Alkali Silicates in Sodium Hydroxide Romain Dupuis,* Roland Pellenq, Jean-Baptiste Champenois, and Arnaud Poulesquen Cite This: J. Phys. Chem. C 2020, 124, 8288−8294 Read Online ACCESS Metrics & More Article Recommendations *sı Supporting Information ABSTRACT: Recent accelerated simulations of the decondensa- tion of silicates by sodium hydroxide open a window on understanding complex mechanisms of the depolymerization of silicate chains. Herein, complex mechanisms of decondensation that involve two water molecules (or OH− groups) are unveiled. The study of two different solutions, having the same chemical composition but in different concentration, help one to draw more general conclusions on the dissociation mechanism in silicate solutions. We find that the dissociation is not always assisted by single water molecules but that in about 20% of the cases two water molecules (or OH−) are present in the near environment. The results underline the importance to consider explicit water solvent in which water molecules are reactive. I. INTRODUCTION the final products we wanted to synthesize. The first one For a long time, efforts have been done to investigate and (named Zsol) is usually used to synthesize some aluminosi- − · control the silicate chemistry.1 9 It is the base for the licate zeolites. The initial concentrations are [Si] = 2.25 mol −1 + · −1 formation or phase transformation of liquids, gels, and L and [Na ] = 1.31 mol L , which correspond to molar minerals, yet it is unclear how water and silicate chains ratios of SiO2/Na2O = 2.44 and H2O/Na2O = 85. A sodium − interplay at the atomic scale, depending on the chemistry of hydroxide solution ([NaOH] = 1.31 mol·L 1) is added to this the solution and on the shape of the interface.10,11 It is mainly solution in order to study the silicate decondensation process, due to the complexity with experimentally characterizing the as explained by Dupuis et al. in 2019.17 The final 12 structure of silicates in solution. Besides, molecular dynamics concentrations are [Si] = 1.125 mol·L−1 and [Na+] = 1.31 · −1 fi have helped to rationalize the outcomes of experiments. Until mol L ( nal molar ratios are SiO2/Na2O = 1.72 and H2O/ recently, it was also challenging to reproduce the bond Na2O = 85). The second one (named Gsol) is commonly used formation or dissociation by atomistic simulations due to the to synthesize alkali-activated materials as geopolymers. Two high activation energy barrier (a few tenths of an electronvolt) − solutions were characterized by varying the concentration of to make or break Si−O bonds,13 15 but new methods have 14,16,17 sodium hydroxide at fixed silicate and water content ([Si] = See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles. been used to produce reliable silicate structures. This −1 + −1 Downloaded via MASSACHUSETTS INST OF TECHNOLOGY on June 10, 2020 at 18:43:54 (UTC). 5.8 mol·L and [Na ] = 9.66 mol·L , which correspond to opens the paths to study in detail the statistics of the molar ratios of SiO2/Na2O = 1.2 and H2O/Na2O = 11.5, and mechanisms of decondensation for silicate chains. Indeed, − − ff fi [Si] = 5.8 mol·L 1 and [Na+] = 13 mol·L 1, which correspond long-time trajectories o er a large set of con gurations of 9 interest to observe multiple bond-breaking incidents. to molar ratios of SiO2/Na2O = 0.89 and H2O/Na2O = 11.5). In this work, we employ statistical analysis to describe the The NMR spectra corresponding to the two solutions are dissociation mechanisms, triggered by the addition of sodium presented in Figure 1 in the initial state and after hydroxide, that has been reproduced by accelerated molecular decondensation. As usually observed, the mean connectivity dynamics. The loss of connectivity is compared to experiments of the silicate species decreases when the ratio SiO2/Na2O for two different solutions. Both systems contain sodium decreases.9,18 silicates in solution. In particular, we detail how several water − molecules or OH groups could participate in bond Received: February 20, 2020 dissociation. Revised: March 16, 2020 Published: March 25, 2020 II. METHODS II.A. Experimental Samples. The chemical composition of the two sodium silicate solutions were adjusted according to © 2020 American Chemical Society https://dx.doi.org/10.1021/acs.jpcc.0c01495 8288 J. Phys. Chem. C 2020, 124, 8288−8294 The Journal of Physical Chemistry C pubs.acs.org/JPCC Article Figure 1. NMR spectra as a function of the chemical composition for (a) Zsol and (b) Gsol. II.B. Simulated Solutions. In order to study the decondensation of Gsol and Zsol upon the addition of sodium hydroxide, we have first built two structures for the simulation. The stoichiometry and the connectivity of the initial structure have been chosen to be in agreement with the experimental data obtained for Zsol (see Table 1). The two structures that has been simulated are given in Figure 2. The colloidal liquid is composed of 50 SiO4 groups, initially organized in 4 silicate species, 2344 water molecules, and 28 Na+ and OH− groups. The simulation cell size has been set to 42 × 42 × 42 Å3 in order to correspond to the experimental density of 1.135 kg/m3. The system Gsol is composed of 40 SiO groups, initially organized in 14 silicate 4 fi species ranging from monomers to quadrimers, 294 water Figure 2. Snapshot of the original con gurations. Silicon, oxygen, and molecules, and 94 Na+ and OH− groups. The simulation cell sodium atoms are represented in yellow, red, and blue, respectively. The water molecules have been omitted for clarity. size has been set to 30 × 20 × 20 Å3, in agreement with the experimental density that has been measured experimentally (about 1.35 kg/m3). described. The temperature has been controlled using the II.C. Simulation Details. In order to simulate the effect of Nose−́Hoover thermostat.26 Brief-PT runs were simulated adding sodium hydroxide to these two systems, we have used a using the NVT ensemble. If the average distribution of the Qn method based on the parallel tempering (PT) technique, does not evolve for 1000 steps, the convergence is achieved. which consists of replicating the initial state and running For both systems, the convergence has been reached after dynamics at different temperatures in order to enhance energy about 200 ps of PT; note that this does not correspond to real barrier crossing. After 10 steps, if it is energetically favorable, time. The Qn distributions have been compared to nuclear replicas are exchanged.19,20 As detailed by Dupuis et al.,16 in magnetic resonance measurements made after decondensation. brief-PT, the simulation is interrupted regularly (herein every The agreement with the experiments is good for both solutions 1000 steps) and all replica are repopulated with the (see Table 1). In the view of previous works, the brief-PT configuration that has been obtained at the lowest temperature. technique enables one to study decondensation in quantitative A set of 16 temperatures ranging from 300 to 800 K has been agreement with experimental data.16,17 used. II.D. Statistical Analysis. In order to study the In order to account for chemical reactions, we have used the decondensation mechanism, we have proceeded to a statistical reactive force field ReaxFF21 using the parameters given by analysis along the trajectories that have been simulated. In Hahn et al.,22 in which parameters for Na are refitted on the particular, we have developed an algorithm to study the basis of the parameters of Fogarty et al.23 The parameters for mechanism of decondensation (see Figure 3). In this Si/O/H have been previously tested and used to study various algorithm, we are seeking for water molecules or hydroxides silicate systems.16,22,24,25 In particular, it is possible to that enter the near environment during the dissociation, which reproduce the polymerization and depolymerization of silicates defines one event. The environment of the dissociation, as using this set of parameters. Moreover, for silica-base gel shown in Figure 3, is the space defined by the sum of two ffi formation, this set of parameters has shown good e ciency to spheres of radius Rc centered on the position of the two silicon simulate the polymerization of pure silica gels.14 atoms that are being dissociated. After each dissociation, we All simulations have been carried out with LAMMPS code rewound the dynamics and counted the number of events that using the python interface. The time step was set to 0.2 fs to occurred during the last 250 000 steps of the simulation. Since ensure that the dynamics of water molecules is correctly water molecules can be dissociated in the near environment 8289 https://dx.doi.org/10.1021/acs.jpcc.0c01495 J.
Load more

Recommended publications
  • Ionization, Dissociation, and the Investigation of Structure in Small Molecular Models to Develop a Broader Understanding of Gas Phase Ion Chemistry
    Ionization, dissociation, and the investigation of structure in small molecular models to develop a broader understanding of gas phase ion chemistry DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Matthew Bernier Graduate Program in Chemistry The Ohio State University 2014 Dissertation Committee: Professor Vicki Wysocki, Advisor Professor Terry Gustafson Professor Abraham Badu-Tawiah Copyright by Matthew Bernier 2014 Abstract This dissertation focuses on molecular systems in the low-mass range to determine how chemical and structural changes can affect subsequent fragmentation chemistry and protonation site. Each system was investigated using MS analysis and gas-phase ion structural techniques selected from tandem MS (MSMS), hydrogen-deuterium exchange (HDX), ion-mobility (IM), and action infra-red multi-photon dissociation (IRMPD). In Chapter 3, the non-standard amino acid gamma-aminobutyric acid (GABA) was placed into a peptide system to test a mechanism which explained the lack of a3 ions in standard peptide fragmentations. GABA extends the peptide backbone by two methylene units and its insertion into the second position of larger peptides increases the intensity of a3 ion. Using MSMS, it was found that this was a result of blocking common favorable fragmentation pathways. The results demonstrated the use of modified peptides for revealing reasons for how peptides fragment. Chapter 4 focused on a unique set of non-canonical amino acids and their ability to affect the trans/cis nature of adjacent amide bonds in peptide sequences. In solution, 4- R-Flouroproline (R-Flp) is found to favor the trans peptide bond and 4-S-fluoroproline (S- flp) favors the cis bond.
    [Show full text]
  • Drugs and Acid Dissociation Constants Ionisation of Drug Molecules Most Drugs Ionise in Aqueous Solution.1 They Are Weak Acids Or Weak Bases
    Drugs and acid dissociation constants Ionisation of drug molecules Most drugs ionise in aqueous solution.1 They are weak acids or weak bases. Those that are weak acids ionise in water to give acidic solutions while those that are weak bases ionise to give basic solutions. Drug molecules that are weak acids Drug molecules that are weak bases where, HA = acid (the drug molecule) where, B = base (the drug molecule) H2O = base H2O = acid A− = conjugate base (the drug anion) OH− = conjugate base (the drug anion) + + H3O = conjugate acid BH = conjugate acid Acid dissociation constant, Ka For a drug molecule that is a weak acid The equilibrium constant for this ionisation is given by the equation + − where [H3O ], [A ], [HA] and [H2O] are the concentrations at equilibrium. In a dilute solution the concentration of water is to all intents and purposes constant. So the equation is simplified to: where Ka is the acid dissociation constant for the weak acid + + Also, H3O is often written simply as H and the equation for Ka is usually written as: Values for Ka are extremely small and, therefore, pKa values are given (similar to the reason pH is used rather than [H+]. The relationship between pKa and pH is given by the Henderson–Hasselbalch equation: or This relationship is important when determining pKa values from pH measurements. Base dissociation constant, Kb For a drug molecule that is a weak base: 1 Ionisation of drug molecules. 1 Following the same logic as for deriving Ka, base dissociation constant, Kb, is given by: and Ionisation of water Water ionises very slightly.
    [Show full text]
  • Gas-Phase Ion Chemistry: Kinetics and Thermodynamics
    Gas-Phase Ion Chemistry: Kinetics and Thermodynamics by Charles M. Nichols B. S., Chemistry – ACS Certified University of Central Arkansas, 2009 A thesis submitted to the Faculty of the Graduate School of the University of Colorado in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Chemistry and Biochemistry 2016 This thesis entitled: Gas-Phase Ion Chemistry: Kinetics and Thermodynamics Written by Charles M. Nichols has been approved for the Department of Chemistry and Biochemistry by: _______________________________________ Veronica M. Bierbaum _______________________________________ W. Carl Lineberger Date: December 08, 2015 A final copy of this thesis has been examined by all signatories, and we find that both the content and the form meet acceptable presentation standards of scholarly work in the above mentioned discipline. Nichols, Charles M. (Ph.D., Physical Chemistry) Gas Phase Ion Chemistry: Kinetics and Thermodynamics Thesis directed by Professors Veronica M. Bierbaum and W. Carl Lineberger Abstract: This thesis employs gas-phase ion chemistry to study the kinetics and thermodynamics of chemical reactions and molecular properties. Gas-phase ion chemistry is important in diverse regions of the universe. It is directly relevant to the chemistry occurring in the atmospheres of planets and moons as well as the molecular clouds of the interstellar medium. Gas-phase ion chemistry is also employed to determine fundamental properties, such as the proton and electron affinities of molecules. Furthermore, gas-phase ion chemistry can be used to study chemical events that typically occur in the condensed-phase, such as prototypical organic reactions, in an effort to reveal the intrinsic properties and mechanisms of chemical reactions.
    [Show full text]
  • Arrhenius Theory of Dissociation • Dissociation Happens Spontaneously When Ionic (Soluble) Compounds Dissolve in H2O
    Arrhenius Theory of Dissociation • Dissociation happens spontaneously when ionic (soluble) compounds dissolve in H2O. • The more ions are present (i.e. the better it dissociates), the more electricity is conducted. http://antoine.frostburg.edu/chem/senese/101/reactions/slides/sld006.htm Classification of electrolytes • Strong – soluble ionic substances (salts), mineral acids, bases – Acids: HCl, HBr, HI, HNO3, H2SO4, HClO4 – Bases: LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, Ba(OH)2 • Weak – carboxylic acids, amines • Non-electrolytes – most organic compounds • The words “strong” and “weak” refer only to how well something dissociates and forms ions, NOT if it is dangerous, reactive, etc. Determining concentrations of ionic solutions • For the [ ] of ions, we need to consider both the formula and whether or not it dissociates completely (strong electrolyte) What is stoichiometry? • (Probably) the most important topic in chemistry! • This is the basis for many subsequent chapters • Related to the amount of a species or substance • Sometimes referred to as the mathematics of chemistry Some definitions • Molar mass (aka molecular weight) – sum of atomic masses (weights) for all the atoms in a given molecule. – Use the periodic table and the molecular formula to determine this • Formula mass (formula weight) – sum of the masses for all the ions in a given formula unit The periodic table An Important Interpretation • The stoichiometric coefficients that are present in a balanced chemical reaction are related to the ratios of reactants and products in a chemical reaction • This ratio is only in terms of moles (or molecules), BUT NOT mass! Example • The final step in the production of nitric acid involves the reaction of nitrogen dioxide with water; nitrogen monoxide is also produced.
    [Show full text]
  • Na2co3(S) → 2 Na (Aq) +
    Bellevue College CHEM& 121 Experiment: Ionic Solutions (Electrolyte Solutions)* Introduction Molecular compounds are made up of molecules, while ionic compounds are made up of ions. Ions are different from molecules, as they have a charge. In an ionic compound, the number of positively charged cations and negatively charged anions are such that charges are balanced. For example, in the diagram below, note that there are two sodium cations (+1) to balance the charge of each carbonate anion (-2). Many ionic compounds dissolve in water; many do not. If an ionic compound dissolves in water, it separates into individual charged ions. For example, when the soluble compound sodium carbonate dissolves in water, the partial negatively charged side of the polar water molecules surround the positively charged sodium ions, while the partial positively charged side of the polar water molecules surround the negatively charged carbonate ions. The resulting solution is composed of separate sodium ions and carbonate ions surrounded by water molecules. O H H H H O Na+ H Na+ O H 2– H Na+ CO H 2– O 3 O CO 3 H O H H H Na+ 2– CO Na+ 3 The following chemical equation communicates how the soluble ionic compound, sodium carbonate, separates into sodium ions, and carbonate ions. The notation “(aq)” means “aqueous” or that the ion is dissolved in water. Note that water is not written as a reactant, but over the reaction arrow. H2O + 2- Na2CO3(s) à 2 Na (aq) + CO3 (aq) Once ionic compounds are dissolved, the ions in solution may undergo further chemical reactions with other substances, including neutralization, precipitation, oxidation-reduction, and other reactions.
    [Show full text]
  • Chapter 3: Solution Chemistry
    Previous Chapter Table of Contents Next Chapter Chapter 3: Solution Chemistry Section 3.1: Solubility Rules (For Ionic Compounds in Water) Section 3.1.1: Introduction Solubility is defined as the ability of a compound to dissolve in a solvent, here, in water. Different compounds have different solubility in water. Here, we will only deal with ionic compounds since a number of simple rules exist to decide whether specific ions impart solubility or not. For example, NaCl dissolves very easily in water while CaCO3 dissolves only very sparingly. Molecular compounds can also exhibit a wide range of solubility in water (for example sugar is very soluble in water, while oil and gasoline are not). The discussion of solubility of molecular compounds is however postponed until Chapter 10 where we study “Intermolecular Forces and Liquid Properties”. Section 3.1.2: Solubility Rules for Chlorides, Bromides and Iodides All chloride, bromide and iodide ionic compounds are soluble in water except those containing silver(I), mercury(I), lead(II) and copper(I). Section 3.1.3: Dissociation of Chlorides, Bromides and Iodides Practice making chloride, bromide and iodide compounds with main group and transition metals and learn whether these compounds are soluble and if so, what species form upon dissolution in water. Section 3.1.4: Solubility Rules for Acetate, Chlorate, Perchlorate, Nitrate and Hydroxide Compounds All acetate, chlorate, perchlorate and nitrate ionic compounds are soluble in water. All group 1 hydroxide compounds are soluble in water. Magnesium, calcium, strontium and barium hydroxides are only slightly soluble. All other hydroxides are insoluble in water.
    [Show full text]
  • Acid Dissociation Constant and Related Thermodynamic Quantities for Triethanolammonium Ion in Water from 0 to 50 °C
    JOURNAL OF RESEARCH of the National Bureau of Standards- A. Physics and Chemistry Vol. 64A, No.4, July- August 1960 Acid Dissociation Constant and Related Thermodynamic Quantities for Triethanolammonium. Ion in Water From o to 50 °C l Roger G . Bates and Guy F. Allen (February 25, 1960) Earlier studies of the dissociation constants of monoethanolammoniu m and diethanolam­ monillm ions and the thermodynamic constants for t he dissociation processe have been supplemented by a simi lar study of triethanolammonium ion from 0° to 50° C. The dis­ sociation constant (II. bh) is gi ven by the formula - log K b,, = 1341.l6j T + 4.6252 - 0.0045666T where T is in degrees Kelvin. The order of acidic strcngths of the ions is as folloll"s: Tri­ ethanolamm.onium> diethallolammonium> rnonethanolammooium. Conversely, rnono­ ethanolamine is the strongest of the three bases. The thermodyna mic constants for the dis ociation of one mole of triethanolammonium ion in the standard state at 25° C are as fol lows: Heat contcnt change (6H O) , 33,450 joule mole-I; entropy change (6S0) , - 36.4 joule deg- I mole-I; heat-capaeit.v cha nge (6C;), 52 joule deg-I mole-I. 1. Introduction standard changes of heat content, entropy, and heat capacity accompanying the dissociation process have t The dissociation of positively charged weak acids been computed from the temperature coefficient of ( is . 1111 isoclectric proce s, occurring without the the dissociation constant. As cxpected, triethanol­ creation of new electrostatic charges. There should amine is It weak:er base than diethanolamine, which f therefore be no significant electrostatic contribution is, in turn, weaker thfm monoeLhanolamine.
    [Show full text]
  • A General Mechanism for Competitor-Induced Dissociation of Molecular Complexes
    ARTICLE Received 28 Apr 2014 | Accepted 9 Sep 2014 | Published 24 Oct 2014 DOI: 10.1038/ncomms6207 A general mechanism for competitor-induced dissociation of molecular complexes Thayaparan Paramanathan1,2,3,w, Daniel Reeves2,3, Larry J. Friedman1, Jane Kondev2,3 & Jeff Gelles1,2 The kinetic stability of non-covalent macromolecular complexes controls many biological phenomena. Here we find that physical models of complex dissociation predict that competitor molecules will, in general, accelerate the breakdown of isolated bimolecular complexes by occluding rapid rebinding of the two binding partners. This prediction is largely independent of molecular details. We confirm the prediction with single-molecule fluore- scence experiments on a well-characterized DNA strand dissociation reaction. Contrary to common assumptions, competitor-induced acceleration of dissociation can occur in biologically relevant competitor concentration ranges and does not necessarily imply ternary association of competitor with the bimolecular complex. Thus, occlusion of complex rebinding may play a significant role in a variety of biomolecular processes. The results also show that single-molecule colocalization experiments can accurately measure dissociation rates despite their limited spatiotemporal resolution. 1 Department of Biochemistry, Brandeis University, PO Box 549110, Waltham, Massachusetts 02454-9110, USA. 2 Materials Research Science and Engineering Center (MRSEC), Brandeis University, PO Box 549110, Waltham, Massachusetts 02454-9110, USA. 3 Department of Physics, Brandeis University, PO Box 549110, Waltham, Massachusetts 02454-9110, USA. w Present address: Department of Physics, Bridgewater State University, Bridgewater, Massachusetts 02325, USA. Correspondence and requests for materials should be addressed to J.K. (email: [email protected]) or to J.G. (email: [email protected]).
    [Show full text]
  • Electrochemistry Solutions of Electrolytes Dissociation of Water Dissociation of Water and the Acidity Constant Ph of Strong
    1/28 2/28 Electrochemistry co04 Solutions of electrolytes co04 Subject of electrochemistry: strong electrolyte: (almost) completely ionizes (dissociates) no uncharged molecules in the solution dissociation (solutions of electrolytes, melts of salts) H2SO4, KOH, Ca(OH)2, NaCl, BaSO4,... conductivity not necessarily to max. degree: 100 % partially 2 phenomena at interfaces s/l (electrolysis, galvanic cells) H2SO4 H+ + HSO4 2 H+ + SO4 → − → − weak electrolyte: contains neutral (not dissociated) molecules Conductors: organic acids and bases, NH3,H2O, . electrons (or holes) are moving: standard states: solvent (water): ; in dilute 1 • water = metals, graphite, graphene, semiconductors c st ions: [ ] ( = γc/c ) ions are moving (or jumping): dissociation constant = equilibrium constant of the dissociation reaction solutions of electrolytes , molten salts, ionic liquids + CH3 COOH CH3 COO− + H both electrons and ions are moving: → + NH3 + H2O NH4 + OH− plasma → + (COOH)2 HOOC-COO− + H → pH log = log10, p = log − γ + =1 c + c + H H H ? + ? + pH = log H+ = log = log = log[H ] = log{H } cst mol dm 3 − − − − − − 3/28 4/28 Dissociation of water co04 Dissociation of water and the acidity constant co04 Dissociation of water: Acidity constant (ionization constant) Ka is common in tables = equilibrium con- + stant of deprotonisation, often given as pKa H2O H + OH− → acids: dissociation constant of the acid Ionic product (autoionization constant) of water Kw: + H+ OH cH+ cOH . CH3 COOH CH3 COO + H Ka = Kd K − − H+ OH 1.00 10 14 25 C − w = st 2 [ ][ −] = − ( ◦ ) → H2O ≈ (c ) ≡ × bases: dissociation constant of the conjugated acid Equivalently (at 25 C): ◦ NH4+ NH3 + H+ (Ka) ( 1) pH + pOH = pKw = 14 more accurate 13.997 → × − H O H+ OH K 1 2 + − ( w) (+ ) → × depends on temperature: pK (100 C) = 12.29 w ◦ NH H O NH + OH K K /K heavy water: pK (25 C) = 14.87 3 + 2 4 + − d = w a w ◦ → (isotopic effect: D is more strongly bound) Example.
    [Show full text]
  • Electrochemistry
    33Unit Objectives ElectrElectrochemistrochemistryy After studying this Unit, you will be able to • describe an electrochemical cell and differentiate between galvanic Chemical reactions can be used to produce electrical energy, and electrolytic cells; conversely, electrical energy can be used to carry out chemical reactions that do not proceed spontaneously. • apply Nernst equation for calculating the emf of galvanic cell and define standard potential of the cell; Electrochemistry is the study of production of • derive relation between standard electricity from energy released during spontaneous potential of the cell, Gibbs energy chemical reactions and the use of electrical energy of cell reaction and its equilibrium to bring about non-spontaneous chemical constant; transformations. The subject is of importance both • define resistivity (ρ), conductivity for theoretical and practical considerations. A large ( ) and molar conductivity (¥ ) of κ m number of metals, sodium hydroxide, chlorine, ionic solutions; fluorine and many other chemicals are produced by • differentiate between ionic electrochemical methods. Batteries and fuel cells (electrolytic) and electronic conductivity; convert chemical energy into electrical energy and are • describe the method for used on a large scale in various instruments and measurement of conductivity of devices. The reactions carried out electrochemically electrolytic solutions and can be energy efficient and less polluting. Therefore, calculation of their molar study of electrochemistry is important for creating new conductivity; technologies that are ecofriendly. The transmission of • justify the variation of sensory signals through cells to brain and vice versa conductivity and molar and communication between the cells are known to conductivity of solutions with have electrochemical origin. Electrochemistry, is change in their concentration and therefore, a very vast and interdisciplinary subject.
    [Show full text]
  • Water Kit© Ph Lesson
    . .where molecules become real TM Water Kit © pH Lesson Objectives Students will: • Create a physical representation of the autoionization of water using the water kit. • Describe and produce a physical representation of the dissociation of a strong acid and a strong base. + - • Associate a high hydronium ion (H3O ) concentration with low pH and a high hydroxide ion (OH ) concentration with a high pH. • Demonstrate how the structure of an amino acid is affected by the pH of the environment into which it has been placed. Materials • 1 Water Kit© cup per small group • 1 copy of this packet per person Water Dissociation The water kit may also be used to introduce the concepts of water dissociation (autoionization) and pH to students. A small percentage of water molecules (about 1 in 10,000,000) break apart in pure water at room temperature. Positively charged hydrogen ions (H+) and negatively charged hydroxide ions (OH-) are formed in this dissociation. Remove two water molecules from the water cup. Begin the dissociation of water by pulling off a hydrogen from one of the water molecules. Sketch the model representation of the first step in the dissociation of water. + + - H (aq) OH (aq) H2O(l) + - H2O(l) H (aq) + OH (aq) When water dissociates, one of the hydrogen nuclei leaves its electron behind with the oxygen atom to become a hydrogen cation (H+). The hydrogen ion is not stable and bonds to the oxygen atom of a + second unionized water molecule to form a hydronium ion (H3O ). Sketch the model representation of the next step in the dissociation of water with hydronium ion formation.
    [Show full text]
  • Chapter 16 Acid-Base Equilibria
    Chapter 16 Acid-Base Equilibria Learning goals and key skills: + + Understand the nature of the hydrated proton, represented as either H (aq) or H3O (aq) Define and identify Arrhenuis acids and bases. Define and identify Bronsted-Lowry acids and bases, and identify conjugate acid-base pairs. Relate the strength of an acid to the strength of its conjugate base. Understand how the equilibrium position of a proton transfer reaction relates the strengths of acids and bases involved. + - Describe the autoionization of water and understand how [H3O ] and [OH ] are related + - Calculate the pH of a solution given [H3O ] or [OH ] Calculate the pH of a strong acid or strong base given its concentration Calculate Ka or Kb for a weak acid or weak base given its concentration and the pH of the solution Calculate pH of a weak acid or weak base or its percent ionization given its concentration and Ka or Kb. Calculate Kb for a weak base given Ka of its conjugate acid, and similarly calculate Ka from Kb. Predict whether and aqueous solution of a salt will be acidic, basic, or neutral Predict the relative strength of a series of acids from their molecular structures Define and identify Lewis acids and bases. 1 Acids and Bases Arrhenius -An acid is a substance that, when dissolved in water, increases the concentration of hydrogen ions. -A base is a substance that, when dissolved in water, increases the concentration of hydroxide ions. Brønsted-Lowry -An acid is a proton donor. -A base is a proton acceptor. Acids and bases may be inorganic (7 strong acids, 8 strong bases) or organic (acids have –COOH group): • HCl, HNO3 H2SO4, HBr, HI, HClO3, HClO4 • AOH (A = Li, Na, K, Rb, Cs); A(OH)2 (A = Ca, Sr, Ba) What happens when an acid dissolves in water? • Water acts as a Brønsted-Lowry base and abstracts a proton (H+) from the acid.
    [Show full text]