Lec-32-Chap16-1

Lec-32-Chap16-1 - Chapter 16: Chapter 16: Acids and Bases...

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1 Chapter 16: Acids and Bases Arrhenius : any substance which ionizes in water to produce: Better version of the Arrhenius definition : Acid: Acid: Hydronium ions (H 3 O + ) in water are acidic. Base Base: Hydroxide ions (OH - ) in water are basic. So, w So, why is NH 3 (aq) basic? • Protons is an Acid Acid • Hydroxide ions is a Base Base Arrhenius Definition
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2 An alternative definition: NH 3 (g) + H 2 O( l ) NH 4 + (aq) + OH - (aq) Base: H + acceptor Acid: H + donor Br Br ønsted nsted -Lowry Acid Lowry Acid = Proton donor Br Br ønsted nsted -Lowry Base Lowry Base = Proton acceptor Works for non-aqueous solutions and explains why NH 3 is basic: Brønsted-Lowry Concept Water acts as a base when an acid dissolves in water: HBr(aq) + H 2 O (l) H 3 O + (aq) + Br - (aq) acid base acid base Water is amphiprotic amphiprotic -i t ±can ± donate or accept a proton (act as acid or base). But water acts as an acid for some bases: H 2 O (l) + NH 3 (aq) NH 4 + (aq) + OH - (aq) acid base acid base Water’s Role as Acid or Base
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3 Weak Weak acids and bases do not fully ionize. Strong Strong acids and bases almost completely ionize. HNO 3 (aq) + H 2 O( l )H 3 O + (aq) + NO 3 - (aq) Note: the products are a new acid and base pair. HF(aq) + H 2 O( l 3 O + (aq) + F - (aq) H 2 O( l ) + NH 3 (aq) NH 4 + (aq) + OH - (aq) Base: H + acceptor Acid: H + donor Base: H + acceptor Acid: H + donor Brønsted-Lowry Concept Molecules or ions related by the loss/gain of one one H + . Conjugate Acid Conjugate Base H 3 O + H 2 O CH 3 COOH CH 3 COO - NH 4 + NH 3 H 2 SO 4 HSO 4 - HSO 4 - SO 4 2- HC l C l - donate H + accept H + NH 4 + and NH 2 - are not not conjugate (conversion requires 2 H + ) Conjugate Acid-Base Pairs
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4 An alternative definition: NH 3 (g) + H 2 O( l ) NH 4 + (aq) + OH - (aq) Base: H + acceptor Acid: H + donor Br Br ønsted nsted -Lowry Acid Lowry Acid = Proton donor Br Br ønsted nsted -Lowry Base Lowry Base = Proton acceptor Works for non-aqueous solutions and explains why NH 3 is basic: Brønsted-Lowry Concept Identify the base conjugate to HF(aq) and the acid conjugate to HCO 3 - (aq) HCO 3 - + H + H 2 CO 3 HF H + + F - ( CO 3 2- is the base conjugate to HCO 3 - ) Conjugate Acid Base: H + acceptor Conjugate Base Acid: H + donor Conjugate Acid-Base Pairs
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5 Strong acids are better H + donors than weak acids Strong bases are better H + acceptors than weak bases ± Strong acids have weak conjugate bases. (reverse rxn) ± Weak acids have strong conjugate bases. Strong acid + H 2 OH 3 O + + conjugate base Fully ionized, reverse reaction essentially does not occur. The conjugate base is weak. Weakly ionized, reverse reaction readily occurs.
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Lec-32-Chap16-1 - Chapter 16: Chapter 16: Acids and Bases...

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