4_acid_base

4_acid_base - Acid-Base Reactions Read section 2-1 not...

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Sec.4 - Acid-base 1 Acid-Base Reactions Bronsted-Lowry acid substance that can donate a hydrogen ion (H + ) Bronsted-Lowry base substance that can accept a hydrogen ion (H + ) CH 3 COOH + ¯OH CH 3 COO ¯ + H 2 O acid baseconjugate 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 Volhardt: 2-1, 2-2, 8-3, 9-1, 13-2, 19-4 Read section 2-1 not covered in notes Acid-base movie
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Sec.4 - Acid-base 2 pH = -log[H + ] pOH = -log[OH] k w = [H + ][ ¯ OH] = 1 x 10 -14 pH + pOH = 14 neutral solution [H + ] = [ ¯OH] = 1 x 10 -7 pH = 7 acidic solution [H + ] > 1 x 10 -7 pH range 0 to 7 basic solution [H + ] < 1 x 10 -7 pH range 7 to 14 Review General formula for an acid HA; for a base B H A H + + A ¯ B + H 2 O B + H + ¯OH k a = [H + ][A¯] k b = [ ¯ OH][B + H] [HA] [B] taking the log of both sides Henderson-Hasselbalch equations pH = pk a + log[A ¯ ] pOH = pk b + log[B + H] [HA] [B] strong acid [H + ] , k a , pk a strong base [¯OH] , k b , pk b weak acid [H + ] , k a , pk a weak base [¯OH] , k b , pk b relationship between conjugate acid base pairs k a x k b = k w =1 x 10 -14 pk a + pk b = 14 Brønsted-Lowry acids and bases
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Sec.4 - Acid-base 3 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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Sec.4 - Acid-base 4 Opposite Charges Attract and React BF 3 has substantial positive charge on the boron NH 3 has substantial negative charge localized at the lone pair -ve goes to +ve
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Sec.4 - Acid-base 5 BF 3 is sp 2 hybridized The LUMO (Lowest Unoccupied Molecular Orbital) is shown to the right. Most of the volume of the LUMO corresponds to the empty p orbital The base donates its electrons that occupy the HOMO to the LUMO of the acid to produce a new sigma bond NH 3 is sp 3 hybridized. The HOMO (Highest Occupied Molecular Orbital) is shown to the left and is where the nonbonding lone pair resides. The van der Waals surface electron density is indicated by the mesh
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Sec.4 - Acid-base 6 Why do acids have different acidities? What makes a strong acid a strong acid? An acid is strong if it’s conjugate base is stable. If the base is not stable it is reactive and will react with a proton and shift the equilibrium to the left in the following equilibrium. H A + H + Hence the strength of an acid is inversely related to the strength of its conjugate base. What makes the base stable? You must look at the structure of the molecule. What is the hybridization of the atom? Is the charge on an electronegative atom? Is the electronegative atom large so that the charge is spread over a larger area ? Can the charge be delocalized throughout the molecule? All of these must be considered Acidity increases with increasing anion stability The first step to organic reactions is understanding acids and bases
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Sec.4 - Acid-base
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This note was uploaded on 07/10/2010 for the course CHEM 266 taught by Professor Pols during the Spring '07 term at Waterloo.

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4_acid_base - Acid-Base Reactions Read section 2-1 not...

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