CHEM 251 1st Edition Lecture 19 Outline of Last Lecture I. Clicker QuestionII. Solar FuelsIII. The Fisher-Tropsch ProcessIV. Future Synthetic FuelsOutline of Current Lecture V. Clicker QuestionsVI. Solvent and Acids in WaterVII. Bronsted Acid/BaseCurrent LectureVIII. Clicker Questionsa. What solvent would you recommend for removing grease stains from a shirt?i. Water, benzene, ammonia, tetrachloroethyleneii. “perc” = dominant solvent used in dry cleaningb. which class of solvent will have lowest pKa for NH3?i. Non-polar, polar aprotic, polar proticIX. Solvent and Acids in Watera. Solvent: liquid that can dissolve chemical reagentsb. Nonpolar: solvent through dispersion forcesi. Good for nonpolar covalent small moleculesii. Ex: hexanes, diethyl etheriii. Good at dissolving fats and oilsc. Polar aprotic: solvation through dispersion forces, polarization, and cation stabilizationi. Good for some polar covalent small molecules and some ionic latticesii. Ex: acetonitrileiii. Lewis bases that coordinate to cationsd. Polar protic: solvation through polarization, cation stabilization, and anion stabilization (H bond)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.i. Good for ionic lattices, sometime unable to dissolve non-polar small moleculesii. Good for hydrophilic materialsiii. Ex: water, alcohols, aminesiv. The lattice enthalpy overcome by separate stabilization of cation and anionv. Cations stabilized by ion-dipole interactions (dative lone pair donation)vi. Anions stabilized by hydrogen-bonding from the protic part of the solventvii. Note that ionic bonds are broken-a dissociation event is also occurringviii. Water versus ammonia – different performance of polar protic solventsix. An acid is a substance that produces H3O+ (in water) or NH4+ (in ammonia)x. Acidity scales can be derived for any solvent (even aprotic)xi. Acidity limited by pKa of the acid [pKa(H3O+) = –1.74, pKa(NH4+) = 9.25]xii. A “leveling effect” is observed when acids stronger than the pKa of the acidic form of the solvent are employed: strong acids are all equally acidicbecause they completely protonate the solvente.f. More polar solvents, especially polar protic solvents: good at solubilizing ionsg. Non-polar solvents, especially aprotic solvents: good for neutral small moleculesX. Bronsted Acid/Basea. Acid: donates H+b. Base: accepts H+c.d. Acid strength can be rationalized by:i. Electronegativity: how much the conjugate base wants negative chargeii. Resonance stabilization: how much resonance is present in conjugate baseiii. Bond strengths: How strong the H–A bond is (weaker are more
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