Chem 113 1st Edition Lecture 25Outline of Last Lecture I. Reactions of acids and bases in waterII. Relative strengths of some acids and basesOutline of Current Lecture III. What makes a base weak?IV. Resonance stabilization of (-) chargeV. Size of an ion: also a delocalization of chargeVI. Electronegativity as a last resortVII. Assessing Acidity/BasicityVIII. pH and the autoionization of waterCurrent LectureI. What makes a base weak?a. Delocalization of charge via resonance offers the best stabilizationi. The (-) charge is spread over multiple atomsb. The size of the ion offers the next best stabilizationi. The basicity of (-) ions decreases as you go down a groupc. Electronegativity is the last thing to consider and is used to differentiate the basicity of ions with smaller sizesi. The basicity of (-) ions decreases as you move left to right across a periodII. Resonance stabilization of (-) chargea. The smaller the value of Ka, the weaker the acidb. Delocalization charge by resonance means the negative charge can be distributeddifferently throughout the atom’s resonance structuresThese 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.c. The strongest bases have the least amount of resonance structures, the charge is the most localizedIII. Size of an ion: also a delocalization of chargea. The larger the size of a (-) ion, the less basic it isi. HBr>HCl>HF1. Most to least acidicii. F->Cl->Br-1. Most to least basic2. Fluoride ion is the smallest atom in the seriesIV. Electronegativity as a last resorta. The acidity of hydrogens increases as you go left to right across a periodi. F-H>HO-H>H2N-H>H3C-H (Most to least acidic)1. Bond energies do not correlate with the hydrogen’s acidityii. H3C->H2N->HO->F- (Most basic to least basic)1. Pauling electronegativity increases as a base’s strength decreasesV. Assessing Acidity/Basicitya. The highest Ka value means it’s the most acidicb. The highest Kb value means it’s the most basicVI. pH and the autoionization of watera. Water dissociates very slightly into ions in an equilibrium process known as autoionization or self-ionizationb. Acts as an acid and a base with itselfc. The ion-product constant for water (Kw)i. In Kc=[H3O+][OH-]=1.0x10-14ii. Both ions are present in all aqueous systemsiii. The water ionization equilibrium is a special kind of equilibrium and is referred to specifically as
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