Chapter16 Acids and Bases SY 1 13 19 CHAPTER 16 Acids and Bases Figure to come Collection of household acids and bases Effect of acids on fish Incorporate pH Include molecular models Chapter 16 16 1 Introduction to Acids and Bases 16 2 Amphiprotic Properties of Water 16 3 Acid and Base Strength 16 4 Estimating the pH of Acid and Base Solutions 16 5 Acid Base Properties of Salts Hydrolysis 16 6 Molecular Structure and Control of AcidBase Strength Caption to come Chapter In Context This chapter continues our discussion of chemical equilibria applying the concepts and techniques developed in Chapter 15 to the chemistry of acids and bases In upcoming chapters we will continue to study chemical equilibria as it applies to acid base reactions buffers and the chemistry of sparingly soluble compounds Acids and bases control the properties of substances all around us This goes beyond chemistry to almost all areas of science and technology Some examples include Biology Can food cook at room temperature Ceviche is a dish prepared by marinating fish in a citrus solution usually containing lime or lemon juice The acidic nature of the marinate cooks the fish by denaturing proteins leaving the flesh firm and opaque as if it had been cooked using heat All proteins are affected by exposure to strong acids or bases including enzymes specialized proteins that catalyze metabolic reactions For example two of the enzymes that help break down food proteins during digestion are active under very different conditions Pepsin the digestive enzyme secreted in the stomach is most active under the very acidic conditions found in the stomach pH 1 5 and is completely inactive when the pH is above 6 Trypsin another digestive enzyme is found in the intestines and is most active under basic conditions pH 7 7 and completely inactive under the strongly acidic conditions found in the stomach Environmental Studies Studies have shown that even a small change in the pH of a lake or river can kill plants and animals Most trout species cannot reproduce if the pH drops below 5 and a pH less than 4 5 will kill adult trout Strongly acidic conditions in lakes and rivers also affect the concentration of metal ions in the water such as aluminum High aluminum concentrations affect fish by clogging their gills resulting in death by suffocation In Your Home Did you ever wonder why ammonia is found in so many cleaning products Most household cleaners contain bases such as ammonia sodium hydroxide or ethanolamine that help dissolve acidic greasy solids Acidic cleaning products will remove lime and rust stains basic metal oxides and hydroxides 16 1 Chapter Goals Use the Br nsted Lowry acid and base definitions Understand the consequences of water autoionization Apply the principles of aqueous equilibria to acids and bases in aqueous solution Identify the acid base properties of aqueous salt solutions Recognize the influence of chemical structure and bonding on acidbase properties Chapter16 16 1 Acids and Bases SY 1 13 19 Introduction to Acids and Bases OWL Opening Exploration 16 1 Acidity Basicity of Household Chemicals Acids and bases are important components in household products industrial processes and in environmental and biological systems As shown in OWL Activity 16 1 many of the items you might find in your home are acids and bases We begin our study of acids and bases where we left off in Chapter 5 with the Arrhenius acid and base definitions Arrhenius Acid Flashback 5 XX Acids and Bases A substance containing hydrogen that when dissolved in water increases the concentration of H ions A substance containing the hydroxide group that when dissolved in water increases the concentration of OH ions Arrhenius Base The Br nsted Lowry definition is a broader description of the nature of acids and bases This definition allows us to define a larger number of compounds as acids or bases and to describe acid base reactions that take place in solvents other than water such as ethanol or benzene for example Ammonia NH3 is not an Arrhenius base its formula does not contain a hydroxide group but it is defined as a Br nsted Lowry base when it accepts a proton from an acid such as HCl Br nsted Lowry Acid Br nsted Lowry Base A substance that can donate a proton H ion A substance that can accept a proton H ion The Lewis acid base definitions are broader still and are often used to describe reactions that take place in the gas phase For example borane BH 3 is acting as a Lewis acid when it accepts a lone pair from a Lewis base such as ammonia NH3 Lewis Acid Lewis Base A substance that can accept an electron pair A substance that can donate an electron pair Most of the acid base reactions we will study take place in aqueous solution so we will use the Br nsted Lowry definitions when referring to acids and bases The chemistry of Lewis acids and bases will be discussed in Chapter 18 OWL Concept Exploration 16 2 Br nsted Lowry Acids and Bases Simple Acids and Bases A Br nsted Lowry acid base reaction involves the transfer of a proton from an acid to a base For example in the following reaction H transfer Flashback 15 1 The Principle of Microscopic Reversibility HF aq NH3 aq F aq NH4 aq acid base a proton H is transferred from the acid HF the proton donor to the base NH 3 the proton acceptor When viewed from the reverse direction 16 2 15 XX Microscopic Reversibility Chapter16 Acids and Bases SY 1 13 19 H transfer HF aq NH3 aq F aq NH4 aq base acid a proton is transferred from the acid NH4 to the base F The overall equilibrium is represented as HF aq NH3 aq F aq NH4 aq H H F ACID donates H to NH3 N H H H F BASE accepts H from NH3 N H base accepts H from NH4 H H acid donates H to F The acid in the forward reaction HF and the base in the reverse reaction F differ only by the presence or absence of H and are called a conjugate acid base pair The other conjugate acid base pair in this reaction is NH 4 NH3 Because the Br nsted Lowry definitions are based on the donating or accepting a proton every Br nsted Lowry acid has a conjugate base every Br nsted Lowry base has a conjugate acid and every Br nsted Lowry acid base reaction involves two conjugate acid base pairs H H H F acid Chapter Goals Revisited Use the Br nsted Lowry acid and base definitions Identify conjugate acid base pairs H H F base N H H H N H H acid base H H EXAMPLE PROBLEM Acid base conjugate pairs a What is the conjugate acid of the iodate ion IO 3 What is the conjugate base of formic