Chemistry
Acid-Base Reactions
Acid-base reactions involve the transfer of protons (H+) from an acid to a base. When an acid and a base react, they form water and a salt. Acids are substances that donate protons, while bases are substances that accept protons. This type of reaction is fundamental in understanding the behavior of many chemical compounds and is important in various industrial and biological processes.
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10 Key excerpts on "Acid-Base Reactions"
- Henry Freiser, Monika Freiser(Authors)
- 1992(Publication Date)
- CRC Press(Publisher)
Chapter 4 Acid Base Equi l i brium THEORIES OF ACIDS AND BASES Of the many theories that have been proposed through the years to explain the properties of acids and bases, the Bf0nsted-Lowry, or proton transfer theory, and the older, more general Lewis theory are most generally useful. The Br0nsted-lowry Theory In 1923 Bf0nsted and Lowry each developed an acid-base theory based on the central role of the proton. They defined an acid as a proton donor and a base as a proton acceptor. Thus, an acid-base reaction is one in which proton transfer occurs, Le., Acid ' Base + H + (4-1) According to this definition, neutral molecules such as H 3 P04 or H 2 0, cations such as NH / , and anions like H 2 P0 4 -all behave as acids, e.g., (4-2) Similarly, cations (H 2 NCH 2 CH 2 NH 3 + ) , anions (HC 2 0 4 -), and neutral mole-cules can all act as bases. Certain substances such as H 2 0 and SH-behave as acids as well as bases, and are called ampholytes or amphiprotic substances. SR ' H + + S = acid base H + + SH-' H 2 S base acid Equation 4-2 is a simplification of the proton transfer reaction that takes place if the reaction is carried out in a solvent such as water. Free protons 53 54 Concepts & Calculations in Analytical Chemistry do not exist in any solvent. The characterization of a substance as an acid or a base must be made in terms relative to the solvent, i.e. water. That is to say, an acid is a substance capable of donating a proton to water, and a base is a substance capable of accepting a proton from water. Reaction 4-2 is therefore more correctly represented as follows: (4-3) The hydrated proton is represented as H 3 0 + . Although it is, strictly speaking, incorrect to write H + to represent a hydrated proton, this is generally accepted for the sake of convenience. Throughout this book, H + and H 3 0 + will be used interchangeably. It is evident from Equation 4-3 that there is a proton transfer from the acid, NH4 + , to the water molecule, H 2 0.
eBook - ePubInorganic Chemistry for Geochemistry and Environmental Sciences
Fundamentals and Applications
- George W. Luther, III(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
Chapter 7 Acids and Bases 7.1 Introduction Acids and bases have been known since before Roman times, for their ability to transform a chemical substance into other chemical forms. For example, sulfuric acid (, oil of vitriol; vitriolic acid) could be produced by the aqueous oxidation of pyrite, which is a common mineral used for many purposes [1]. dehydrates sugar as well as metal hydrates with sometimes dramatic color changes, and also dissolves metals via redox reactions. It is normally the chemical that is produced and sold in greatest quantity in the world each year. The first base was called lye, which was obtained by leaching ashes with water producing potassium hydroxide solution. Lye is a common name for bases, which are used in a variety of purposes including wood degradation into paper or fibers and soap production. 7.2 Arrhenius and Bronsted–Lowry Definitions Common acids such as hydrochloric acid (HCl) and nitric acid were not formally prepared until about the 16th century, so formal definitions of acids and bases similar to bonding theories are relatively new. In 1884, Svante Arrhenius defined an acid as a chemical species that when dissolved in water produced the hydrogen ion,. Although useful, the definition is limited as it does not encompass a large variety of reactions and only considers water as solvent. In 1923, Brønsted and Lowry defined an acid and base reaction as one that involves a hydrogen ion transfer between two reactants. The acid is the hydrogen ion donor (the Brønsted acid) and the base is the hydrogen ion acceptor (the Brønsted base). This definition applies to all solvents and the gas phase. For example, the reaction between HCl and can occur in water as solvent or in the gas phase (an atmospheric reaction) and results in complete transfer to form the hydronium ion,
eBook - PDF- David R. Klein(Author)
- 2020(Publication Date)
- Wiley(Publisher)
In order to prepare ourselves for the study of ionic reactions, it is critical to be able to identify acids and bases. We will learn how to draw Acid-Base Reactions and to compare the acidity or basic- ity of compounds. These tools will enable us to predict when Acid-Base Reactions are likely to occur and to choose the appro- priate reagent to carry out any specific acid-base reaction. 94 CHAPTER 3 Acids and Bases DO YOU REMEMBER? Before you go on, be sure you understand the following topics. If necessary, review the suggested sections to prepare for this chapter. • Identifying Formal Charges (Sections 1.4 and 2.4) • Identifying Lone Pairs (Section 2.5) • Drawing and Interpreting Bond-Line Structures (Section 2.2) • Drawing Resonance Structures (Section 2.10) 3.1 INTRODUCTION TO BRØNSTED-LOWRY ACIDS AND BASES This chapter will focus primarily on Brønsted-Lowry acids and bases. There is also a brief section deal- ing with Lewis acids and bases, a topic that will be revisited in Chapter 6 and subsequent chapters. The definition of Brønsted-Lowry acids and bases is based on the transfer of a proton (H + ). An acid is defined as a proton donor, while a base is defined as a proton acceptor. As an example, con- sider the following acid-base reaction: O Cl Cl Acid (proton donor) O Base (proton acceptor) H H H H H H + + ⊕ ⊝ In the reaction above, HCl functions as an acid because it donates a proton to H 2 O, while H 2 O func- tions as a base because it accepts the proton from HCl. The products of a proton transfer reaction are called the conjugate base and the conjugate acid: + + HCl Acid Cl – Conjugate base Base H 2 O Conjugate acid H 3 O + In this reaction, Cl − is the conjugate base of HCl. In other words, the conjugate base is what remains of the acid after it has been deprotonated. Similarly, in the reaction above, H 3 O + is the conjugate acid of H 2 O. We will use this terminology throughout the rest of this chapter, so it is important to know these terms well.
eBook - ePub- Jeffrey Gaffney, Nancy Marley(Authors)
- 2017(Publication Date)
- Elsevier(Publisher)
− ) when dissolved in water. This definition only held for ionic compounds containing hydrogen or hydroxide ions and did not apply to many acids and bases that we deal with today. Since this early definition of acids and bases was so limited, two more sophisticated and general definitions of acids and bases have since been developed, which are in wide use today. These are known as the Brønsted-Lowry definition and the Lewis definition.In 1923, both J.N. Brønsted of Denmark and Thomas Lowry of England, working independently, defined an acid as a species that can donate a hydrogen ion to a base. A base was defined as a species that can accept a hydrogen ion from an acid. So, a Brønsted-Lowry acid is a proton (H+ ) donor and a Brønsted-Lowry base is a proton (H+ ) acceptor. Both acids and bases are divided into two categories, strong and weak. The Brønsted-Lowry measure of the strength of an acid is determined by the ability of the acid to give up a proton. The measure of the strength of a base is the ability of the base to attract a proton. The relative strength of an acid is often described quantitatively in terms of an acid ionization constant (K a ), which will be covered in detail in Section 5.3 .An acid-base reaction, then, involves the transfer of a proton from an acid to a base to form a new acid and a new base. When an acid loses its proton, it becomes a conjugate base and when a base gains a proton it becomes a conjugate acid . The term “conjugate” comes from Latin and means “joined together .” It particularly refers to things that are joined together in pairs. The Brønsted-Lowry acid-base reaction can be summarized by the generalized chemical equation;HA Acid+B Base→A Conjugate base+HB Conjugate acid(1)So, a conjugate acid is a species formed by the addition of a proton (H+ ) to a base. A conjugate base is a species formed by the removal of a proton from an acid. The acid and its conjugate base as well as the base and its conjugate acid are known as conjugate pairs , whose chemical formulas are related by the gain or loss of a hydrogen ion. Some examples of acids and their conjugate bases are given in Table 5.1 . Notice how the conjugate pairs in Table 5.1
eBook - PDFIntroductory Chemistry
An Active Learning Approach
- Mark Cracolice, Edward Peters, Mark Cracolice(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
1. An acid–base reaction is a transfer of protons; a redox reaction is a transfer of electrons. 2. In both cases, the reactants are given special names to indicate their roles in the transfer process. An acid is a proton source; a base is a proton remover. A reducing agent is an electron source; an oxidizing agent is an electron remover. 3. Just as certain species can either provide or remove protons (e.g., HCO 3 2 and H 2 O) and thereby behave as an acid in one reaction and a base in another, certain species can either remove or provide electrons, acting as an oxidizing agent in one reaction and a reducing agent in another. An example is the Fe 21 ion, which can oxidize Zn atoms to Zn 21 in the reaction Fe 21 saqd 1 Znssd S Zn 21 saqd 1 Fessd Fe 21 can also reduce Cl 2 molecules to Cl 2 ions in another reaction: 2 Fe 21 saqd 1 Cl 2 sgd S 2 Cl 2 saqd 1 2 Fe 31 saqd 4. Just as acids and bases may be classified as stronger or weaker depending on how readily they remove or provide protons, the relative strengths of oxidizing and reducing agents may be compared according to their tendencies to attract or release electrons. 5. Just as most acid–base reactions in solution reach a state of equilibrium, most aqueous redox reactions also reach equilibrium. Just as the favored side of an acid–base equilibrium equation can be predicted from acid–base strength, the favored side of a redox equilibrium equation also can be predicted from oxidizing agent–reducing agent strength. 17.9 The Water Equilibrium Goal 12 Given the hydrogen ion or hydroxide ion concentration of water or a water solution, calculate the other value. In the remaining sections of this chapter, you will be multiplying and dividing expo- nentials, taking the square root of an exponential, and working with logarithms. We will furnish brief comments on these operations as we come to them. For more detailed instructions, see Appendix I, Parts A and C.
eBook - PDFChemistry
Structure and Dynamics
- James N. Spencer, George M. Bodner, Lyman H. Rickard(Authors)
- 2011(Publication Date)
- Wiley(Publisher)
The Brønsted model explains water’s role in acid–base reactions. ● Water dissociates to form ions by transferring an H ion from one mole- cule acting as an acid to another molecule acting as a base. Acid Base ● Acids react with water by donating an H ion to a neutral water molecule acting as a base to form the H 3 O ion. Acid Base ● Bases react with water by accepting an H ion from a water molecule act- ing as an acid to form the OH ion. Base Acid ● Water molecules can act as intermediates in acid–base reactions by gaining H ions from an acid. Acid Base and then losing the H ions to a base. Base Acid Adding these reactions so that species that are on both sides of the equation can- cel gives the overall equation for the acid–base reaction. It is important to recognize that acid–base reactions don’t have to occur in water; they can also occur in the gas phase. Many students encounter this phe- nomenon in their first chemistry courses. When bottles of concentrated hydrochlo- ric acid and concentrated aqueous ammonia are both open at the same time, a white cloud of ammonium chloride often forms in the air above these bottles. 11.6 To What Extent Does Water Dissociate to Form Ions? At 25C, the density of water is 0.9971 g/cm 3 , or 0.9971 g/mL. The concentra- tion of pure water is therefore 55.35 M.
eBook - ePubA Mole of Chemistry
An Historical and Conceptual Approach to Fundamental Ideas in Chemistry
- Caroline Desgranges, Jerome Delhommelle(Authors)
- 2020(Publication Date)
- CRC Press(Publisher)
This is an important result since, later on, H + is replaced by H 3 O + ! Because of the concomitance of the two proposals and their essentially equivalent conclusions, the overall theory is now called the Brönsted–Lowry theory. “The simplest and most adequate definition of acids and bases is given by the scheme A = B + H + where A and B represent acid and base respectively. This scheme indicates that an acid is defined as a substance, which is able to split off H + -ions simultaneously forming a base, and a base as a substance capable of uniting with H + -ions, thus forming an acid.” When the acid–base equilibrium occurs in water or in another solvent, the H + -ions are solvated. Specifically, in water, A + H 2 O = B + H 3 O +. This “is a double acid-basic equilibrium, A and H 3 O + acting as acids, B and H 2 O as bases”. Another consequence is that acids and bases can either be ions or neutral molecules. For instance, if the acid A is a neutral molecule like formic acid HCOOH, then the base B is an anion called formate anion HCCO −. The chemical equation is then HCOOH + H 2 O = HCCO − + H 3 O +. Indeed, the equation is balanced since there are 4H and 3O on both sides of the equation. The charges are also balanced (the neutrality is ensured on both sides). If the base B is now a neutral molecule such as methylamine CH 3 NH 2 then the acid A is, in this case, a cation called methylammonium cation CH 3 NH 3 +. Again, the chemical equation can be written as CH 3 NH 3 + + H 2 O = CH 3 NH 2 + H 3 O +. As we can see, the numbers of C, N and H are the same on both sides of the equation. Also, there is the same charge (+1) on either side of the equation. This means that, in the Brönsted–Lowry theory, an acid and a base work as a pair or, differently put, as conjugates. Indeed, the conjugate base of an acid is what is left after a proton has been removed from the acid. As an example, the acetate ion CH 3 COO − is the conjugate base of acetic acid CH 3 COOH
eBook - PDFChemistry for Today
General, Organic, and Biochemistry
- Spencer Seager, Michael Slabaugh, Maren Hansen, , Spencer Seager, Spencer Seager, Michael Slabaugh, Maren Hansen(Authors)
- 2021(Publication Date)
- Cengage Learning EMEA(Publisher)
(Section 9.5) 6 Write reaction equations that illustrate the characteristic reactions of acids. (Section 9.6) 7 Write reaction equations that represent neutralization reactions between acids and bases. (Section 9.7) 8 Write reaction equations that illustrate various ways to prepare salts, and do calculations using the concept of an equivalent of salt. (Section 9.8) 9 Demonstrate an understanding of the words weak and strong as applied to acids and bases. (Section 9.9) SDI Productions/E+/Getty Images Copyright 2022 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Acids, Bases, and Salts 261 ACIDS, BASES, AND SALTS are among the most common and important sol- utes found in solutions. Until late in the 19th century, these substances were char- acterized by properties, such as taste and color changes induced in certain dyes. Acids taste sour (see Figure 9.1); bases, bitter; and salts, salty. Litmus, a dye, is red in the presence of acids and blue in the presence of bases. These and other obser- vations led to the correct conclusions that acids and bases are chemical opposites and that salts are produced when acids and bases react with each other. Today, acids and bases are defined in more precise ways that are useful when studying their characteristics. 9.1 The Arrhenius Theory Learning Objective 1 Write reaction equations that illustrate Arrhenius acid–base behavior. In 1887, Swedish chemist Svante Arrhenius proposed a theory dealing with electro- lytic dissociation. He defined an acid as a substance that dissociates when dissolved in water and produces hydrogen ions (H 1 ).
- Frederick Bettelheim, William Brown, Mary Campbell, Shawn Farrell(Authors)
- 2019(Publication Date)
- Cengage Learning EMEA(Publisher)
240 | Chapter 8 Acids and Bases Copyright 2020 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 8.6 Properties of Acids and Bases Today’s chemists do not taste the substances they work with, but 200 years ago they routinely did so. That is how we know that acids taste sour and bases taste bitter. The sour taste of lemons, vinegar, and many other foods, for example, is due to the acids they contain. A. Neutralization The most important reaction of acids and bases is that they react with each other in a process called neutralization. This name is appropriate be-cause, when a strong corrosive acid such as hydrochloric acid reacts with a strong caustic base such as sodium hydroxide, the product (a solution of ordinary table salt in water) has neither acidic nor basic properties. We call such a solution neutral. Section 8.9 discusses neutralization reactions in detail. B. Reaction with Metals Strong acids react with certain metals (called active metals) to produce hydrogen gas, H 2 , and a salt. Hydrochloric acid, for example, reacts with magnesium metal to give the salt magnesium chloride and hydrogen gas ( Figure 8.1 ). 1 Mg( s ) Magnesium MgCl 2 ( aq ) Magnesium chloride H 2 ( g ) Hydrogen 2HCl( aq ) Hydrochloric acid 1 The reaction of an acid with an active metal to give a salt and hydrogen gas is a redox reaction (Section 4.4). Both the acid and the salt formed are ion-ized in aqueous solution.
- Peter V. Hobbs(Author)
- 2000(Publication Date)
- Cambridge University Press(Publisher)
5 Acids and bases Very early in the history of chemistry many substances were designated as acids, bases, and salts. Acids have a sour taste (e.g., citric acid gives lemon juice its sour taste); they dissolve certain metals; and they also dissolve carbonate minerals to produce carbon dioxide. Bases have a bitter taste (e.g., sodium carbonate); they feel slippery when touched; and they react with many dissolved metal salts to form precipitates. However, the most striking characteristic of bases is their ability to neutralize the properties of acids; when a base reacts with an acid a salt is produced. The French chemist Lavoisier thought that all acids contain oxygen (the word oxygen means acid former in Greek). However, it was sub-sequently found that many acids contain no oxygen (e.g., hydrochloric acid, HC1), but that they all contain hydrogen. Acids and bases figure prominently in the equilibrium of aqueous solu-tions, where they significantly enhance the electrical conductivity of water. In this chapter, we will explore some of the important properties of acids and bases in aqueous solutions. This will lead us to a discussion of several theories of acids and bases. 5.1 Some definitions and concepts Equation (4.22) is valid for aqueous solutions as well as for pure water. A solution for which [H + (aq)] = [OH~(aq)] is said to be neutral; thus, pure water is neutral. If [H + (aq)] > [OH~(aq)] the solution is said to be acidic. If [OH(aq)] > [H + (aq)] the solution is said to be basic. Exercise 5.1. If 0.02 mole of hydrochloric acid is dissolved in 1L 1 of water, what are the concentrations of H + (aq) and OH(aq) ions I in the solution at 25°C? I 83 84 Acids and bases Solution. Hydrochloric acid is a gas under normal conditions, but it is a strong electrolyte that dissolves in water to form equal numbers of H + (aq) and Q(aq).
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