Section_4_Acid-Base_post

Section_4_Acid-Base_post - Acid-Base Reactions Volhardt:...

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Sec.4 - Acid-base 1 Acid-Base Reactions Volhardt: 2-1, 2-2, 8-3, 9-1, 13-2, 19-4 Read section 2-1 not covered in notes Brønsted-Lowry acid substance that can donate a proton (H + ) Brønsted-Lowry base substance that can accept a proton (H + ) CH 3 COOH + ¯OH CH 3 COO ¯ + H 2 O acid base conjugate base conjugate acid Lewis acid substance that can accept a pair of electrons Lewis base substance that can donate a pair of electrons FeBr 3 + Br 2 FeBr 4 + Br Lewis acid Lewis base Lewis base Lewis acid +
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Sec.4 - Acid-base 2 Lewis Acids and Bases Makes you think about the electrons and how bonds are formed arrow show bond formation arrow show bond breaking new bond gained two electrons and becomes negatively charged
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3 The first step to understanding organic chemistry reactions is understanding acid-base reactions. H A A - + H + There are many factors that affect the strength of the conjugate base: the electronegativity of the charged atom, the size of the charged atom, the inductive effects of electron-donating and electron-withdrawing groups, possible delocalization of the charge, and the hybridization of the atom. Acidity increases with increasing anion stability (conjugate base stability) OR the less reactive the conjugate base, the stronger the acid is, since the equilibrium is shifted toward H + . Acid-Base Strength Why do acids have different acidities and what makes an acid strong? The acidity of an acid ( H A ) depends on the stability of its conjugate base ( A - ), and vice Versa. Therefore, an acid is strong if it’s conjugate base is stable or “unreactive”. WHY? If the base ( A - ) is not stable then it is reactive. The more reactive the base ( A - ), the more likely it will react with the proton ( H + ) and shift the equilibrium back toward the acid ( H A ). So, what makes the conjugate base stable?
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Acidity increases with increasing conjugate base stability: The more electronegative an atom is, the greater its ability to stabilize a negative charge. Remember, electronegativity is the measure of an elements affinity for an electron OR its ability to accept an electron. B 2.0 C 2.5 N 3.0 O 3.5 F 4.0 Al 1.5 Si 1.8 P 2.1 S 2.5 Cl 3.0 Ga 1.8 Ge 2.0 As 2.2 Se 2.6 Br 2.8 Te 2.1 I 2.5 Given the periodic table on the right, what is the order of increasing electronegativity of the underlined atom (which becomes negatively charged)? (CH 3 ) 3 C ¯ + H + (CH 3 ) 2 N ¯ + H + CH 3 O ¯ + H + F ¯ + H + H A + H + B) HF > CH 3 OH > CH 3 ) 2 NH > (CH 3 ) 2 CH A) 1 > 2 > 3 > 4 B) 4 > 3 > 2 > 1 C) 4 > 2 > 3 > 1 D) 1 > 4 > 3 > 2 Acid-Base Strength: What Atom is the Charge On? 1. 2. 3. 4. (CH 3 ) 3 C -H (CH 3 ) 2 N -H CH 3 O -H H-F Example: Given the following four acids, arrange them from stongest to weakest: First, draw the conjugate bases formed by each acid: So the order of the strongest to the weakest acid is? F- is the most stable anion since it is the most electronegative atom and has
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This note was uploaded on 11/14/2010 for the course CHEM CHEM266 taught by Professor Forsey during the Fall '10 term at Waterloo.

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Section_4_Acid-Base_post - Acid-Base Reactions Volhardt:...

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