CHEM 113 1nd Edition Lecture 17 Outline of Last Lecture I. Equilibrium problemII. Clicker QuestionIII. Synthesis of AmmoniaIV. Biosynthesis of isoleucine from threonineOutline of Current Lecture o Arrhenius Acid-Base Equilibriao Strong and Weak Acidso Strong and Weak Baseso Acid Dissociation Constanto Autoionization of watero The pH ScaleCurrent LectureChapter 18: Acid-Base Equilibria- Arrhenius Acid-Base definitiono These definitions classify substances in terms of their behavior with watero An acid is a substance with H in its formula that dissociates to produce H3O+o A base is a substance with OH in its formula that dissociates to yield OH-o When an acid reacts with a base, they undergo neutralization Meaning the H+ from the acid and the OH- from the base form H2O For this reaction, no matter how strong or weak the base or acid is, delta H is always -55.9 kJ per mole of water formed.- Strong and Weak acidso A strong acid dissociates completely into ions in water.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. This means in a dilute solution of a strong acid there will be no molecules of that acid remaining. For these reactions, K for concentration is extremely largeo A weak acid dissociates slightly to form ions in water In a dilute solution of a weak acid, most of its molecules will be undissociated. For these reactions, K is a very small value Figure 18.1 depicts this relationship.o Classifying the Relative Strengths of Acids Strong acids include- The hydrohalic acids, HCl, HBr and HI- The oxoacids in which the number of O atoms exceeds the number of ionizable protons by two or moreo Ex. HNO3, H2SO4, HClO4 Weak acids include- The hydrohalic acid HF- Acids in which H is not bonded to O or to a halogen (ex. HCN)- Oxoacids in which the number of O atoms equals or exceeds to number of ionizable protons by one (ex. HClO, HNO2)- Carboxylic acids, which have the general formula RCOOH, where Rrepresents another element or moleculeo Classifying the Relative Strengths of Bases Strong bases include- Water-soluble compounds containing O2- or OH- ions- The cations are usually those of the most active metals- M2O or MOH, where M= Group 1A metal (Li, Na, K, Rb and Cs)- MO or M(OH)2 where M= Group 2A metal (Ca, Sr, and Ba) Weak bases include- Ammonia (NH3)- Amines, which have the general formula - The common structural feature is an N atom with a lone electron pair.o Sample problem 18.1, requires you to be familiar with these ideas- The Acid Dissociation Constant, o This value of K indicates the strength of an acid.o It is still solved the same way The concentrations of products over reactants The physical state rule still applies for this equation, meaning all reactantsand products must be in either an (aq) or (g) state in order to be included in the equation.o A stronger acid means a high [H3O+} and therefore a larger Kao A weaker acid means a lower percentage of dissociation and therefore a smaller Ka- Autoionization of Water o Water dissociates very slightly into ions in an equilibrium process known as autoionization or self-ionization This process takes two H2O molecules and turns them into an H3O+ molecule and an OH- moleculeso The Ion-Product constant for water, Kw The autoionization of water is described quantitatively by an equilibrium constant  Because the concentration of H2O remains essentially constant, we multiply Kc by [H2O]^2 to obtain a new equilibrium constant Notice that one H3O+ ion and one OH- ion form for each H2O molecule that dissociates. Therefore in pure water we find that  This autoinization affects aqueous acid-base chemistry in two major ways- 1). A change in [H3O+] causes an inverse change in [OH-] and vice versa.- 2). Both ions are present in all aqueous systems.o Therefore we can define the terms acidic and basic in terms of the relative concentrations of H3O+ and OH- ionso Note that if you know the value of Kw at a particular temperature and the concentration of one of the two ions, you can find the concentration of the other. For example here is how you would manipulate the equation to find [OH-] Sample problem 18.2 requires the use of this idea- The pH Scaleo pH= -log[H3O+] The pH of a solution indicates its relative acidity The higher the pH, the lower the [H3O+] and the less acidic the solutiono pOH= -log[OH-] This is expressing the hydroxide ion concentration Acidic solutions have a higher pOH than basic solutionso pK=-logK This represents the equilibrium constant A low pK corresponds the a high Ko This represents the relationship among pH, pOH and pK.- Things to noteo The sum of pH and pOH is pKw for any aqueous solution at any temperature and pKw equals 14.00 at 25 Co Sin Kw is a constant, the values of pH,pOH, [H3O+] and [OH-] are interrelated If [H3O+] increases, [OH-] decreases and vice versa If pH increases, pOH decreases and vice