lecture13sf

lecture13sf - Lewis Acid-Base Concept Bronsted-Lowry acid:...

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Lewis Acid-Base Concept Bronsted-Lowry acid: Proton donor Bronsted- Lowry base: Proton Acceptor Lewis acid: Electron-pair acceptor Lewis base: Electron-pair donor Consider the reaction: NH 3 + H + → NH 4 + Alternatively: NH 3 + H 3 O + → NH 4 + + H 2 O The NH 3 molecule is clearly a proton acceptor (Bronsted-Lowry base). But it is also an electron- pair donor (Lewis base), since the proton gets added to the lone pair site on the NH 3 molecule. The H + ion is the Lewis acid (electron pair acceptor). Consider the reaction: OH - + H + → HOH Alternatively: OH - + H 3 O + → 2HOH The OH - ion is clearly a proton acceptor (Bronsted-Lowry base). But it is also an electron pair donor (Lewis base), since the proton adds on to one of the lone pairs on the hydroxide ion. The H + is the Lewis acid (electron pair acceptor). Consider the reaction: BF 3 + NH 3 → F 3 B-NH 3 This is not a typical Bronsted-Lowry acid-base reaction. There is no transfer of a proton. But it is a Lewis acid-Lewis base reaction.
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The lone pair of electrons on the NH 3 molecule directly attach to the boron atom of the BF 3 molecule. BF 3 has an incomplete octet, and is sp 2 hybridized with a trigonal planar shape. After the reaction with NH 3 , the boron has four bonds around it with a tetrahedral shape (sp 3 hybrid). The fourth bond comes from the pair of electrons originally on the NH 3 . In this reaction BF 3 is a Lewis acid (electron pair acceptor) and NH 3 is a Lewis base (electron pair donor). Consider the reaction in which aluminum ion gets hydrated by six water molecules: Al 3+ + 6H 2 O → Al(H 2 O) 6 3+ The lone pairs of electrons on the O atom in water attach to the positive aluminum ion. The aluminum ion is the Lewis acid (electron pair acceptor) and the water is the Lewis base (electron pair donor). Consider the reaction between SO 3 and H 2 O to make H 2 SO 4 SO 3 + H 2 O → H 2 SO 4 The SO 3 can be considered a Lewis acid (electron pair acceptor). The water can be considered a Lewis base (electron pair donor). The lone pairs of electrons on water’s oxygen molecule attaches onto the central S of SO 3 . At the same time, an H atom shifts from the water to an oxygen atom on the SO 3 .
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Solubility Product When ionic substances dissolve in water, they dissociate into individual ions. The equilibrium constant for that process is designated as the solubility product, K sp . K sp expression AgCl(s) Ag + (aq) + Cl - (aq) [Ag + ][Cl - ] Ag 2 CrO 4 (s) 2Ag + (aq) + CrO 4 2- [Ag + ] 2 [CrO 4 2- ] PbI 2 (s) Pb 2+ (aq) + 2I - (aq) [Pb 2+ ][I - ] 2 Bi 2 S 3 (s) 2Bi 3+ (aq) + 3S 2- (aq) [Bi 3+ ] 2 [S 2- ] 3 Solubility products are listed for sparingly soluble salts. So K sp is generally a small number. Table 16.1 of your text lists a number of different K
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This note was uploaded on 07/17/2010 for the course 160 162 taught by Professor Kimmel during the Spring '10 term at Rutgers.

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lecture13sf - Lewis Acid-Base Concept Bronsted-Lowry acid:...

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