CH 221 1st Edition Lecture 5Outline of Last Lecture I. Ethane, Ethene, EthyneII. Bonds in:a. Ammoniumb. WaterIII. Bond StrengthIV. ElectronegativityV. Acids and Basesa. Ka and pKaOutline of Current Lecture VI. More Acids and Basesa. Alcoholsb. Aminesc. Pronated AminesVII. Protonated Alcohol and Carboxylic AcidsVIII. Lewis DefinitionsIX. Strength of Acids and BasesCurrent LectureVI. pH= -log[+¿H¿] indicates that the concentration of protons in a solution pH= -log[+ ¿H3O¿].Carboxylic acids are the most common organic acids such as acetic acid and formic acid. a. Alcohols: CH3OHmethyl alcohol pKa= 15.5 (methynol)CH3CH2OHethyl alcohol pKa= 15.9 (ethylnol)b. Amines: CH3NH2 methylamine pKa= 40NH3ammoniapKa= 36c. Protonated Amines: +¿CH3NH3¿ protonated methylamine pKa= 10.7+¿CH3CH2NH3¿protonated ethylamine pKa= 11.0VII. Protonated alcohols and carboxylic acids are much more acidic than their counterparts. Protonated methyl alcohol has a pKa of -2.5, protonated ethyl alcohol has a pKa of -2.4, and protonated acetic acid has a pKa of -6.1. Alcohols can behave as either an acid or base. The curved arrows in some reactions point from the electron donor to the electron acceptor. A 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.carboxylic acid also acts as both an acid and a base and has reactions very similar to those of alcohols. VII. Lewis definitionsAcids- the species that accepts a share in an electron pairBases- the species that donates a share in an electron pair. All Bronsted acids are Lewis acids and all Bronsted bases are Lewis bases. An amine can behave as either an acid or a base much like alcohols and carboxylic acids. IX. In reactions, the stronger acid behaves as the acidEx. HCl + H2O the hydrochloric acid is stronger therefore acts as the acidNH3 + H2O The water acts as the acid because its acidity is stronger than that of ammoniaEquilibrium favors the formation of weaker acids. Electronegativity has an effect on the pKa values which in turn effects the pH.Relative Electronegativity C < N < O < FWhen atoms are the same size, the strongest acid has its hydrogen attached to the most electronegative atom. Relative Acidity CH4<NH3<H2O< HFThe stronger the acid, the weaker its conjugate base and vice versa. Alcohols are stronger acids than amines because oxygen is more electronegative than nitrogen. Hybridization also effects electronegativity.Most electronegative sp>sp2>sp3least electronegativeSize also effects pKa valuesSmallest −¿F¿<−¿Cl¿<−¿Br¿<−¿I¿ largestWeaker acid HF <HCl<HBr< HI Stronger
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