DOCSLIB.ORG

Chapter 4 Acids and Bases Read Pages 116-125 on Your Own (Covered in Previous Classes)

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Chapter 4 Acids and Bases Read Pages 116-125 on Your Own (Covered in Previous Classes) CHEM 511 Chapter 4 page 1 of 12 Chapter 4 Acids and Bases Read pages 116-125 on your own (covered in previous classes) Brønsted-Lowry acid: proton donor Brønsted-Lowry base: proton acceptor Typical strong acids? Weak acids? Typical strong bases? Weak bases? Amphiprotic materials? Distribution diagrams CHEM 511 Chapter 4 page 2 of 12 A bit about water, first... Hydrogen bond strength is ~25 kJ/mol, but these are constantly being formed and broken. Water clusters may be formed, such as (H2O)10, which has ice-like structure. At atmospheric pressure, ice crystallizes in a wurtzite structure with oxygen atoms in both Zn and S positions. What is the geometry of Zn and S in wurtzite? For H+ species in water, other clusters are formed. Note the movement of H+ in water: Conductance Hydrated Ion (siemens) diameter (nm) H+ 350 0.90 Na+ 51 0.45 K+ 74 0.30 OH- 192 0.35 Cl- 76 0.30 - NO3 71 0.30 Recall hydrated diameter from the Debye-Hückel Equation...do these numbers make sense? CHEM 511 Chapter 4 page 3 of 12 Characteristics of Brønsted acids Aqua Acid: when an acidic proton is on a coordinated water molecule For comparison HOAc 1.8 10-5 -4 HNO2 4.5 10 -2 H2C2O4 5.9 10 Al3+(aq) 1.4 10-5 Cr3+(aq) 1.6 10-4 Zn2+(aq) 2.5 10-10 Fe2+(aq) 3.2 10-10 Hydroxoacid: the acidic proton is on an -OH group without an oxo (X=O) group Oxoacid: the acidic proton is on an -OH group adjacent to an oxo group The oxidation state can dictate which acid is formed Aqua acid characteristics central atoms have low oxidation states typical of s- and d-block elements metals on left of p-block (Al, In, Ga) Danger!!! Can't always look at aqua acids as an ionic model Good correlation for alkali and alkaline earth metals OK correlation of some d-block metals (Fe2+, Zn2+ , Sc3+, Cr3+) Poor correlation for heavy d-metals and early p-block elements (Hg2+, Sn2+, Tl3+--suggests that there may be covalency to M-O bond CHEM 511 Chapter 4 page 4 of 12 Oxoacid characteristics central atom has a high oxidation number or intermediate oxidation state of p-block element Substituted oxoacids Groups on the central atom can affect acidity Pauling's Rules For an oxoacid: OpE(OH)q, pK ~ 8-5p For each successive pKa value (if polyprotic) increase pKa by 5 CHEM 511 Chapter 4 page 5 of 12 Anhydrous Oxides Acidic oxides either (a) combine with water to release H+ or (b) react with hydroxide Basic oxides either (a) transfer a proton in water or (b) react with an acid In general basic oxides are ionic compounds acidic oxides are covalent compounds Oxides or hydroxides that react with both acids and bases are amphoteric Amphoteric oxides are at the boundary of acidic and basic oxides Circles mean amphoteric oxides in all oxidation states; boxes mean acidic oxides in the highest oxidation states, with amphoteric oxides in lower oxidation states. Amphoterism for d-block elements Most +3/+4 oxidation states for 1st period transition metal oxides higher oxidation states give acidic oxides CHEM 511 Chapter 4 page 6 of 12 Polyoxo compound formation Condensation polymers can form Cation formation: typical of metals. Below are Baes and Mesmer diagrams for Al 3+ -5 3+ 0.1 m Al 1 10 m Al Saturated with Al(OH)3 + As pH is increased, H gets removed until you form Al(OH)3 which precipitates as a gelatinous - mass. Further increasing the pH causes Al(OH)3 to redissolve (1,4 = Al(OH)4 ) CHEM 511 Chapter 4 page 7 of 12 Anion formation Common for early d-block ions or oxides in high oxidation states and non-metal oxides Below are distribution diagrams for Si Phosphorus can form condensation polymers with chains and rings. CHEM 511 Chapter 4 page 8 of 12 Lewis acidity and basicity A Lewis acid is: an electron acceptor A Lewis base is: an electron donor Common examples of Lewis acids 1. Metal and ligand 2. atom with an incomplete octet 3. atoms with ability to rearrange their octet 4. atoms that can expand their octet Group 3A/13 Lewis acids Dimerization of AlCl3 Note this reaction: BX3 + N(CH3)3 X3B-N(CH3)3 Stability of product complex decreases with more electronegative X, BF3 < BCl3 < BBr3 Is this the expected trend with respect to electronegativity of the halogen? Group 4A/14 Not much for C with respect to inorganic chemistry (when considering Lewis acidity) Si (and others) can expand its octet, leading to reactive species CHEM 511 Chapter 4 page 9 of 12 Group 5A/15 (pnictogens) Notable Lewis acid is SbF5 Hard and soft acids and bases - - - - Hard acids bond in order: I < Br < Cl < F and R3P << R3N and R2S << R2O - - - - Soft acids bond in order: F < Cl < Br < I and R2O << R2 S and R3N << R3P Note: Hg2+ binds strongly to I- and weakly F - Note: Al3+ bonds strongly to F- and weakly to Br- Chemical consequences of hard/soft acids/bases? CHEM 511 Chapter 4 page 10 of 12 Solvent Leveling What is the strongest acid observed in water? What is the strongest base in water? Leveling Effect: Inability of a solvent to differentiate among the relative strengths of acids stronger than the solvent's conjugate acid. In all cases, Ka × Kb = Ksolv and pKa + pKb = pKsolv Any acid is leveled if pKa < 0 (i.e., Ka > 1) and any base is leveled if pKb < 0 - Thus, for bases with pKa > pKsolv the base will act like solv CHEM 511 Chapter 4 page 11 of 12 Non-Aqueous solvents Ammonia What reactions have we observed with NH3 previously? In NH3, weak acids may act as strong acids: Precipitation reactions can occur, though lead to differences from water: KCl(aq) + AgNO3(aq) AgCl(am) + KNO3(am) Nitrogen inversion in NH3 Hydrogen Fluoride Both highly reactive AND toxic! Can’t store in glass containers due to reaction with silica—use Teflon, instead. Autoprotolysis pKHF ~11, but the reaction is a bit different than you might expect due to strong hydrogen bonding Only very strong acids can protonate HF... ...otherwise, a weak acid may GET protonated by HF CHEM 511 Chapter 4 page 12 of 12 Sulfuric Acid Autoionization is (surprisingly?) high: pKH2SO4 ~3.6 ...though other reactions also occur: H2SO4 H2O + SO3 + - H2O + H2SO4 H3O + HSO4 SO3 + H2SO4 H2S2O7 + - H2S2O7 + H2SO4 H3SO4 + HS2O7 - Viscosity is a result of hydrogen bonding. Ionic conductivity is very high: how does HSO4 and + H3SO4 move through solution so fast since the solution is so viscous? Boric acid in H2SO4 becomes a powerful acid... - + - H3BO3 + 6H2SO4 [B(HSO4)4] + 3H3O + 2HSO4 K(H2SO4) = 0.4 To make sure water is not present in H2SO4, add SO3 to “scavenge” any water molecules. This gives a chemical called “oleum” or “fuming sulfuric acid”. Superacids Superacids are non-aqueous systems that are many times more acidic (Brønsted) than concentrated aqueous solutions of H2SO4. Created by mixing a strong Brønsted acid with a strong Lewis acid. .
Load more

Recommended publications
  • Practical Course in General and Inorganic Chemistry III
    Practical course in general and inorganic chemistry III. Common acid-base theories The Arrhenius definition - Dissociation of strong/weak acids and bases - Preparation of salts - The limitations of the Arrhenius acid-base theory The Brønsted-Lowry definition - Relative strengths of Brønsted-Lowry acids and bases - Amphiprotic species (the amphoterism) - Types of acid-base reactions - Structures of different boric acids and borax - Preparation of normal salts - Acid salts The Arrhenius acid-base theory (1884) • Acid : dissociate in aqueous solution form hydrogen + or the later-termed oxonium (H 3O ) ions univalent, strong acid: univalent, weak acid: diprotic, strong acid: diprotic, weak acid: triprotic, weak acid: • Stepwise acid dissociation : 1 Relative strength of inorganic oxoacids (Pauling) − + + Om X(OH) n Om+1X(OH) n−1 H acid anhydride m = 3 very strong acid m = 2 strong acid m = 1 weak acid m = 0 very weak acid Arrhenius-bases and anhydrides • Base : in aqueous solution form hydroxide (OH −) ion(s) and cation(s) univalent, strong base: divalent, strong base: univalent, weak base: divalent, weak base: trivalent, weak base: • Base anhydrides = metal-oxides : derived from the base by subtracting the molecules of water • base anhydrides of strong bases: 2 Preparation of salts (Arrhenius) base + acid = salt + water • Preparation of salt from a strong base: • Preparation of salt from a weak base : • If the acid is partially neutralized: acid salt The limitations of the Arrhenius acid-base theory • Although ammonia is well-known as a
    [Show full text]
  • In This Section and in the Next Section on Redox Chemistry, We Will Often Draw on Fundamental Thermodynamic Concepts
    Prerequisites for Section III (1-2 weeks) • In this section and in the next section on redox chemistry, we will often draw on fundamental thermodynamic concepts. You should recall the meaning of ∆H, ∆S, and ∆G for chemical and physical changes — and try to think about systems using these concepts. • ∆G˚ = –RTln Keq This relationship is central to relating chemical thermodynamics and equilibrium. • ∆G = ∆H – T∆S for a process with a specified T and P • The above two relationships can be combined to provide invaluable guidance in understanding how a chemist can manipulate ∆H or ∆S (say, by making changes in ∆S˚/R –∆H˚/RT solvents or molecular substituents) to dramatically shift equilibria: Keq = e e . At room temperature, RT ≈ 2.5 kJ/mol, so this equation means that, for example, a change in solvent that causes ∆H to shift by only ~ 6 kJ/mol will shift the equilibrium constant for a reaction by a factor of 10 (roughly). Acids and Bases a. Brønsted Acidity — aqueous equilibria, solvent leveling, periodic trends, oxoacids, anhydrous acids and bases, amphoterism, polyoxo ions, nonaqueous solvents • Brønsted acid = proton donor, Brønsted base = proton acceptor + • pH = –log[H ], pKa = –logKa; pKb = –logKb • [H+][H+] = 10–14 in aqueous solutions • pKa + pKb = 14 – for any conjugate acid-base pair in dilute aqueous solution • recall concepts of conjugate acids and bases; strong acids have weak conjugate bases, weak acids have strong conjugate bases • Things that affect acidity and basicity of organic acids and bases: the ability of a conjugate base (acid) to delocalize negative (positive) charge through inductive effects or resonance affects the strength of an acid (base).
    [Show full text]
  • Inorganic Chemistry for Dummies® Published by John Wiley & Sons, Inc
    Inorganic Chemistry Inorganic Chemistry by Michael L. Matson and Alvin W. Orbaek Inorganic Chemistry For Dummies® Published by John Wiley & Sons, Inc. 111 River St. Hoboken, NJ 07030-5774 www.wiley.com Copyright © 2013 by John Wiley & Sons, Inc., Hoboken, New Jersey Published by John Wiley & Sons, Inc., Hoboken, New Jersey Published simultaneously in Canada No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except as permitted under Sections 107 or 108 of the 1976 United States Copyright Act, without either the prior written permis- sion of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 646-8600. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008, or online at http://www.wiley. com/go/permissions. Trademarks: Wiley, the Wiley logo, For Dummies, the Dummies Man logo, A Reference for the Rest of Us!, The Dummies Way, Dummies Daily, The Fun and Easy Way, Dummies.com, Making Everything Easier, and related trade dress are trademarks or registered trademarks of John Wiley & Sons, Inc. and/or its affiliates in the United States and other countries, and may not be used without written permission. All other trade- marks are the property of their respective owners. John Wiley & Sons, Inc., is not associated with any product or vendor mentioned in this book.
    [Show full text]
  • General Chemistry/Properties and Theories of Acids and Bases 1 General Chemistry/Properties and Theories of Acids and Bases
    General Chemistry/Properties and Theories of Acids and Bases 1 General Chemistry/Properties and Theories of Acids and Bases Acid-Base Reaction Theories Acids and bases are everywhere. Some foods contain acid, like the citric acid in lemons and the lactic acid in dairy. Cleaning products like bleach and ammonia are bases. Chemicals that are acidic or basic are an important part of chemistry. Helpful Hint! You may need to refresh your memory on naming acids. Several different theories explain what composes an acid and a base. The first scientific definition of an acid was proposed by the French chemist Antoine Lavoisier in the eighteenth century. He proposed that acids contained oxygen, although he did not know the dual composition of acids such as hydrochloric acid (HCl). Over the years, much more accurate definitions of acids and bases have been created. Arrhenius Theory The Swedish chemist Svante Arrhenius published his theory of acids and bases in 1887. It can be simply explained by these two points: Arrhenius Acids and Bases 1. An acid is a substance which dissociates in water to produce one or more hydrogen ions (H+). 2. A base is a substance which dissociates in water to produce one or more hydroxide ions (OH-). Based on this definition, you can see that Arrhenius acids must be soluble in water. Arrhenius acid-base reactions can be summarized with three generic equations: Svante Arrhenius General Chemistry/Properties and Theories of Acids and Bases 2 An acid will dissociate in water producing hydrogen ions. A base (usually containing a metal) will dissociate in water to product hydroxide ions.
    [Show full text]
  • Complex Ions and Amphoterism
    Chemistry 112: Reactions Involving Complex Ions Page 27 COMPLEX IONS AND AMPHOTERISM his experiment involves the separation and identification of ions using Ttwo important reaction types: (i) the formation of complex ions and (ii) the amphoteric behavior of some metal hydroxides. You have already encoun- tered complex ion formation in the analysis of the silver group ions and in the experiment on metal sulfides, but more needs to be said about this topic as an introduction to this experiment. THE FORMATION OF COMPLEX IONS Although we usually write cation formulas in solution as if they were simple ions, such as Al3+, these ions are actually bound to a number of water mol- ecules arranged around the central ion (see figure below). The water molecules in this case are examples of a much larger class of molecules and ions called ligands that form coordinate covalent bonds with a central metal cation. That is, the bond is of the form L: → Mn+, where L has donated δ+ an otherwise unused lone pair of electrons H As noted in the experiment on the to the electron accepting metal ion. In the 3+ δ+ H O Al silver group ions, a ligand is a Lewis water molecule, there are two lone pairs of •• base (a donor of one or more pairs of electrons on the O atom, and either of these δ− electrons), and the metal ion in the may form a coordinate covalent bond with a complex ion is a Lewis acid (an elec- metal cation. Ligands are often small, polar tron pair acceptor).
    [Show full text]
  • Complex Ions and Amphoterism
    Chemistry 112: Reactions Involving Complex Ions Page 27 COMPLEX IONS AND AMPHOTERISM his experiment involves the separation and identification of ions using Ttwo important reaction types: (i) the formation of complex ions and (ii) the amphoteric behavior of some metal hydroxides. You have already encoun- tered complex ion formation in the analysis of the silver group ions and in the experiment on metal sulfides, but more needs to be said about this topic as an introduction to this experiment. THE FORMATION OF COMPLEX IONS Although we usually write cation formulas in solution as if they were simple ions, such as Al3+, these ions are actually bound to a number of water mol- ecules arranged around the central ion (see figure below). The water molecules in this case are examples of a much larger class of molecules and ions called ligands that form coordinate covalent bonds with a central metal cation. That is, the bond is of the form L: → Mn+, where L has donated δ+ an otherwise unused lone pair of electrons H As noted in the experiment on the to the electron accepting metal ion. In the 3+ δ+ H O Al silver group ions, a ligand is a Lewis water molecule, there are two lone pairs of •• base (a donor of one or more pairs of electrons on the O atom, and either of these δ− electrons), and the metal ion in the may form a coordinate covalent bond with a complex ion is a Lewis acid (an elec- metal cation. Ligands are often small, polar tron pair acceptor).
    [Show full text]
  • Articles That May Namic Light Scattering Measurements Related the Upper Freez- Account for Cloud Glaciation at Moderate Supercooling
    Atmos. Chem. Phys., 20, 3291–3315, 2020 https://doi.org/10.5194/acp-20-3291-2020 © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License. Protein aggregates nucleate ice: the example of apoferritin María Cascajo-Castresana1,2,3, Robert O. David3,4, Maiara A. Iriarte-Alonso2, Alexander M. Bittner2,5, and Claudia Marcolli3 1División de Salud, TECNALIA, Parque Tecnológico, Paseo de Mikeletegi, 2, 20009 Donostia, Spain 2CIC nanoGUNE, Tolosa Hiribidea, 76, 20018 Donostia, Spain 3Department of Environmental System Sciences, Institute for Atmospheric and Climate Science, ETH Zurich, 8092 Zurich, Switzerland 4Department of Geosciences, University of Oslo, Oslo, 0315, Norway 5Ikerbasque, Basque Foundation for Science, Ma Díaz de Haro 3, 48013 Bilbao, Spain Correspondence: Claudia Marcolli ([email protected]) Received: 24 September 2019 – Discussion started: 7 October 2019 Revised: 10 February 2020 – Accepted: 17 February 2020 – Published: 20 March 2020 Abstract. Biological material has gained increasing atten- −4 to −11 ◦C and a lower one from −11 to −21 ◦C. Dy- tion recently as a source of ice-nucleating particles that may namic light scattering measurements related the upper freez- account for cloud glaciation at moderate supercooling. While ing range to ice-nucleating sites residing on aggregates and the ice-nucleation (IN) ability of some bacteria can be related the lower freezing range to sites located on misfolded cage to membrane-bound proteins with epitaxial fit to ice, little is monomers or oligomers. The sites proved to persist during known about the IN-active entities present in biological ma- several freeze–thaw cycles performed with the same sam- terial in general.
    [Show full text]
  • Buffer Solution Adapted from WIKI
    技 术 资 料 集 锦 NO：20140924 Buffer solution in Biology adapted from WIKI A buffer solution (more precisely, pH buffer or hydrogen ion buffer) is an aqueous solution consisting Acids and bases of a mixture of a weak acid and its conjugate base, or vice versa. Its pH changes very little when a small amount ofstrong acid or base is added to it and thus it is used to prevent changes in the pH of a solution. Buffer solutions are used as a means of keeping pH at a nearly constant value in a wide variety of chemical applications. Many life forms thrive only in a relatively small pH range so they utilize a buffer solution to maintain a constant pH. One example of a buffer solution found in nature is blood. pH Acid–base reaction Contents Acid–base titration Acid-base extraction Dissociation constant 1 Principles of buffering Acid dissociation constant 2 Applications Acid strength o 2.1 Simple buffering agents Acidity function o 2.2 "Universal" buffer mixtures Buffer solutions o 2.3 Common buffer compounds used in biology Proton affinity 3 Buffer capacity Self-ionization of water 4 Calculating buffer pH Amphoterism o 4.1 Monoprotic acids Acid types o 4.2 Polyprotic acids 5 See also Brønsted 6 References Lewis 7 External links Mineral 0510 81819585 | 189 51576701 | QQ: 2642 166682 | [email protected] 1 无锡天演生物技术有限公司 | 江苏省无锡市智慧路 33 号 7 栋 601 室 技 术 资 料 集 锦 NO：20140924 Organic Strong Superacids Principles of buffering Weak Simulated titration of an acidified solution of a weak acid (pKa = Base types 4.7) with alkali.
    [Show full text]
  • Acid Base Equilibrium Pretest
    Name: ________________________ Class: ___________________ Date: __________ ID: A Acid Base Equilibrium PreTest Multiple Choice Identify the choice that best completes the statement or answers the question. 1. If a reaction is reversible, what are the relative amounts of reactant and product at the end of the reaction? a. no reactant; all product b. no product; all reactant c. some product; some reactant d. The relationship between reactants and products cannot be determined. 2. What happens to a reaction at equilibrium when more reactant is added to the system? a. The reaction makes more products. b. The reaction makes more reactants. c. The reaction is unchanged. d. The answer cannot be determined. 3. Which of the changes listed below would shift the following reaction to the right? 4HCl(g) + O2 (g) 2Cl2 (g) + 2H2 O(g) a. addition of Cl2 b. removal of O2 c. increase of pressure d. decrease of pressure 4. What is the effect of adding more water to the following equilibrium reaction? CO2 + H2 O H2 CO3 a. More H2 CO3 is produced. b. CO2 concentration increases. c. The equilibrium is pushed in the direction of reactants. d. There is no effect. 8 5. In an equilibrium reaction with a Keq of 1 10 , the ____. a. reactants are favored b. reaction is spontaneous c. the products are favored d. reaction is exothermic 7 6. The Keq of a reaction is 4 10 . At equilibrium, the ____. a. reactants are favored b. products are favored c. reactants and products are present in equal amounts d. rate of the forward reaction is much greater than the rate of the reverse reaction 7.
    [Show full text]
  • Chapter 16 Acid-Base Equilibria • Acids and Bases
    Chapter 16 Chapter 16 Acid-Base Equilibria • Acids and bases are found in many common substances and are important in life processes. • Group Work: Make a list of some common acids and bases. How do we know which is which? • There are several models for what constitutes an acid or a base -- three models to be discussed. 16.1 Acids and Bases: A Brief Review • Acid: Base: • tastes sour tastes bitter • stings skin feels slippery • corrosive to metals • releases CO2 from carbonates • turns litmus red turns litmus blue • turns phenolphthalein colorless turns phenolphthalein pink • React together to form a salt with loss of the characteristic acid/base properties Arrhenius Theory • Acid: substance that produces H+ in aqueous solution • Base: substance that produces OH- in aqueous solution • Not realistic: H+ has a radius of 10-13 cm, which gives a very concentrated charge, so + + + it associates with H2O as H(H2O)4 , which we usually simplify to H3O or H (aq) – – – • OH is also associated with H2O as OH(H2O)3 which we usually write as OH (aq). • Limited to aqueous solutions, but we find acid-base behavior with other solvents as well. 16.2 Bronsted-Lowrey Acids and Bases • Acid: donates a proton to another substance • Base: accepts a proton from another substance • Acids: + - HCl(aq) + H2O(l) ! H3O (aq) + Cl (aq) + + NH4 (aq) + H2O(l) ! H3O (aq) + NH3(aq) • Bases: - + NH3(aq) + H2O(l) ! OH (aq) + NH4 (aq) 2- - - CO3 (aq) + H2O(l) ! OH (aq) + HCO3 (aq) Acid-Base Neutralization Reaction • Transfer of a proton (hydrogen ion) Conjugate Acids and Bases • Pair of substances differing only by one H+ 16-1 Chapter 16 + - • HF(aq) + H2O(l) ! H3O (aq) + F (aq) acid 1 base 2 acid 2 base 1 • Acid-Base Neutralization + - • H3O (aq) + OH (aq) ! H2O(l) + H2O(l) acid 1 base 2 acid 2 base 1 • Write a balanced equation showing how the following substances behave as acids in water and identify the conjugate acid-base pairs.
    [Show full text]
  • View in (B) Highlights the View Window for the Optical Microscope
    )ORULGD6WDWH8QLYHUVLW\/LEUDULHV 2021 Chemical Garden Membranes in Temperature-Controlled Microfluidic Devices Qingpu Wang and Oliver Steinbock This is the final accepted manuscript, and the publisher's version of record can be found at https://doi.org/10.1021/acs.langmuir.0c03548 Follow this and additional works at DigiNole: FSU's Digital Repository. For more information, please contact [email protected] Chemical Garden Membranes in Temperature- Controlled Microfluidic Devices Qingpu Wang and Oliver Steinbock* Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306-4390, USA ABSTRACT: Thin-walled tubes that classically form when metal salts react with sodium silicate solution are known as chemical gardens. They share similarities with the porous, catalytic materials in hydrothermal vent chimneys and both structures are exposed to steep pH gradients that, combined with thermal factors, might have provided the free energy for prebiotic chemistry on early Earth. We report temperature effects on the shape, composition, and opacity of chemical gardens. Tubes grown at high temperature are more opaque indicating changes to the membrane structure or thickness. To study this dependence, we developed a temperature-controlled microfluidic device which allows the formation of analogous membranes at the interface of two co-flowing reactant solutions. For the case of Ni(OH)2, membranes thicken according to a diffusion-controlled mechanism. In the studied range of 10-40 °C, the effective diffusion coefficient is independent of temperature. This suggests that counteracting processes are at play (including an increased solubility) and that the opacity of chemical garden tubes arises from changes in internal morphology. The latter could be linked to experimentally observed dendritic structures within the membranes.
    [Show full text]
  • Equilibrium of Brønsted-Lowry Reactions
    Equilibrium of Brønsted-Lowry reactions + - • Acids - + [H ][A ] HA + H2O A + H3O K = a [HA] + - + - [BH ][OH ] • Bases B + H2O BH + OH K = b [B] • There is an inverse relationship between the strength of an acid (base) and its conjugate base (acid) • Chemical reactions always proceed from a stronger acid (base) to a weaker acid (base). Quantification of Acid/Base Strength • Typically equilibrium constants vary dramatically (from <10-10 to >1010) • Chemists thus look at the logarithms + pK = -log K pH = -log[H ] a a pK b = -log Kb – Note that pH is not the same as pKa! http://www.wonderwhizkids.com/popups/13040.html Equilibrium calculations involving acids and bases • Typically calculations involve weak acids or bases, as well as dilute solutions • This means that the degree of dissociation x (how many ions are formed) will be small • Rule of thumb: x will be small if [HA]/Ka > 100 for acids, or if [B]/Kb > 100 for bases Example • Calculate the pH of a 1.00M solution of acetic -5 acid (CH3COOH) given a Ka of 1.8X10 . Solution • Although it may not seem obvious at first, there are really two (competing) acid-base reactions here because there are two components in the mixture – acetic acid and water. To decide which one will dominate, we need to look at the Ka’s. -5 Ka = 1.8X10 -14 Kw = 1.0X10 • Because Ka is so much larger than Kw, we can ignore the + small amount of H3O generated by the autoioniZation of water. Solution • Set up the ICE box for the reaction + - CH3COOH H2O H3O CH3COO Initial 1.00 0 (10-7) 0 Change -x x x Equilibrium1.00-x x x • Set up the expression for Ka and substitute the appropriate values Solution • This is a quadratic equation that must be solved for x.
    [Show full text]