Chapter 16 Notes

Chapter 16 Notes - Chapter 16 Acids and Bases Arrhenius any...

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Unformatted text preview: Chapter 16 Acids and Bases Arrhenius : any substance which ionizes in water to produce: Better version of the Arrhenius definition : Acid: Hydronium ions (H 3 O + ) in water are acidic. Base: Hydroxide ions (OH- ) in water are basic. So, why is NH 3 (aq) basic? • Protons is an Acid. • Hydroxide ions is a Base . Arrhenius Definition An alternative definition: NH 3 (g) + H 2 O(ℓ) NH 4 + (aq) + OH- (aq) Base: H + acceptor Acid: H + donor Brønsted-Lowry Acid = Proton donor Brønsted-Lowry Base = Proton acceptor Works for non-aqueous solutions and explains why NH 3 is basic: Brønsted-Lowry Concept Weak acids and bases do not fully ionize. 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) H 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 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- it 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 Molecules or ions related by the loss/gain of 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- HCl Cl- donate H + accept H + NH 4 + and NH 2- are not conjugate, conversion requires 2 H + . Conjugate Acid-Base Pairs 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 Strong acids are better H + donors than weak acids Strong bases are better H + acceptors than weak bases • Stronger acids have weaker conjugate bases. • Weaker acids have stronger conjugate bases. HCl(aq) + H 2 O(ℓ) → H 3 O + (aq) + Cl- (aq) Relative Strength of Acids & Bases strong acid (100 % ionized) very weak base (no tendency to form HCl) HF(aq) + H 2 O(ℓ) H 3 O + (aq) + F- (aq) weak acid (many HF are un-ionized) F- readily forms HF Relative Strength of Acids & Bases Conjugate acid Conjugate base H 2 SO 4 HSO 4- HBr Br- HCl Cl- HNO 3 NO 3- H 3 O + H 2 O H 2 SO 3 HSO 3- HSO 4- SO 4 2- H 3 PO 4 H 2 PO 4- HF F- CH 3 COOH CH 3 COO- H 2 S HS- H 2 PO 4- HPO 4 2- NH 4 + NH 3 HCO 3- CO 3 2- H 2 O OH- OH- O 2- H 2 H- CH 4 CH 3- Acid strength increasing Base strength increasing strong strong extremely weak extremely weak HF is a stronger acid than NH 4 + ....
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This note was uploaded on 01/27/2012 for the course CH 1213 taught by Professor Xia during the Spring '07 term at Mississippi State.

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Chapter 16 Notes - Chapter 16 Acids and Bases Arrhenius any...

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