Acids & Bases

Acids & Bases - Acids and Bases: Equilibrium 6BH...

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1 Acids and Bases 6BH Slide AB 1 Acids and Bases: Equilibrium 6BH Chapter 10 Acids and Bases 6BH Slide AB 2 Acids and Bases: Definitions-1 Arrhenius Bronsted/Lowry Lewis Acid A compound that generates H + in aqueous solution A "proton" (or H + ) donor An electron pair acceptor Base A compound that generates OH in aqueous solution A "proton" (or H + ) acceptor An electron pair donor All definitions are operationally equivalent; however the Lewis definition is by far the most general
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2 Acids and Bases 6BH Slide AB 3 Acids and Bases: Definitions-2 “H + ”, as a discrete species , does NOT exist in water; rather, it combines with water to give hydronium ion: H + ( aq ) + H 2 O( l ) H 3 O + ( aq ) It is the magnitude of the hydronium ion concentration ([H 3 O + ]; in mol/L) that determines how acidic a solution is! Since H 3 O + is generated from H + , and since H + comes directly from the acid under consideration, measurement of the [H 3 O + ] will have a direct correlation to the strength of the acid! Acids and Bases 6BH Slide AB 4 Acids and Bases: Definitions-3 PROTON : an archaic term still used to describe a hydrogen ion (“H + ”); in acid/base chemistry it is still used to denote an acidic hydrogen and should NOT be confused with the more traditional definition of a proton (a positively charged nuclear particle). PROTON TRANSFER : in acid/base chemistry this is used to denote the transfer of a hydrogen ion from an acid (H-donor) to an acceptor (H-acceptor). WEAK ACID or BASE VS. STRONG ACID or BASE : The strength of an acid or a base is a direct function of the degree of ionization of the acid or base (or, how well it does proton transfer reactions). A relative term.
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3 Acids and Bases 6BH Slide AB 5 Acid Strength Indicators 1) For binary acids (HA), the more polar the H-A bond is, the stronger the acid ( good for same period comparisons ) H-CH 3 vs. H-NH 2 vs. H-OH vs. H-F 2) For binary acids (HA), the weaker the H-A bond, the stronger the acid ( good for same group comparisons ) H-OH vs. H-SH vs. H-SeH H-F vs. H-Cl vs. H-Br vs. H-I Which is more important? Acids and Bases 6BH Slide AB 6 Acid Strength Indicators ( cont ) 3) For oxo acids (XOH), the greater the oxidation number of the central atom ( i.e. the more highly oxidized ) or the greater the number of oxygens attached to the central atom, the stronger the acid HClO vs. HClO 2 vs. HClO 3 4) For oxo acids (XOH) with the same number of oxygens attached to the central atom, the greater the electronegativity of the central atom, the stronger the acid; HClO vs. HBrO vs. HIO
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4 Acids and Bases 6BH Slide AB 7 Acid Strength: Inductive Effect Atoms (or groups of atoms) can be classified as either electron releasing or electron withdrawing; this thru-bond effect is known as the Inductive Effect – For organic acids, the stronger the inductive ( or “thru bond” ) effect of an atom attached to the molecular skeleton within THREE bonds of the hydrogen of interest, the stronger the acid: CC C C O H Bond of Interest 1 2 3 4 4 4 3 3 H of Interest O H H F Bond of Interest O H O H F F Bond of Interest O F H of Interest H of Interest
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This note was uploaded on 04/08/2008 for the course CHEM 6BH taught by Professor Hoeger during the Winter '08 term at UCSD.

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Acids & Bases - Acids and Bases: Equilibrium 6BH...

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