Chapter+18 - Chemistry The Molecular Nature of Matter and...

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Click to edit Master subtitle style 6/6/11 Chapter 18 Acid-Base Equilibria Chemistry The Molecular Nature of Matter and Change Dr. Shamindri M. Arachchige arachsm@vt.edu Davidson 11 1 Office Hours: Location: Davidson 11 Monday 1:45-5:00 PM Wednesday 1:45-4:15 PM Other hours by appointment 11
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6/6/11 22 Chapter 18 Acid-Base Equilibria What are Acids and Bases? Two classes of compounds: acids and bases 3 Definitions of acids and bases: 1. Arrhenius Definition: Acids: Bases: Examples: HCl(aq) NaOH(aq) H+(aq + Cl-(aq) Na+(aq) + OH- (aq) Substances that dissociate in water into H+. Has Hydrogen in the formula Substances that dissociate in water to yield OH-. Has OH in the formula
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6/6/11 33 Chapter 18 Acid-Base Equilibria Brønsted-Lowry Acid-Base Definition An acid is a proton donor, any species which donates a H +. A base is a proton acceptor, any species which accepts a H +. Acids: Bases: HA(aq) + H 2 O H 3 O + (aq) + A - (aq) B(aq) + H 2 O(aq) BH + (aq)+OH(aq) HCl(aq) + H 2 O( l ) H 3 O + (aq) + Cl - (aq) NH 3 (aq) +H 2 O( l ) NH 4 + (aq) +OH - (aq) H 3 O + : Acids deprotonate Bases undergo protonation A is an anion H is accepted to make H3 Hydronioum ion, H+, proton 0 electrons Base, accepts a proton, hydroxides are left d
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6/6/11 44 Chapter 18 Acid-Base Equilibria
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6/6/11 55 Chapter 18 Acid-Base Equilibria Brønsted-Lowry Acid-Base Definition An acid-base reaction can now be viewed from the standpoint of the reactants AND the products. An acid reactant will produce a base product and the two will constitute an acid-base conjugate pair. HC l(aq) + NH 3 (aq) C l - + 4 + Conjugate acid: Conjugate base: Example Problem : What is the conjugate acid of H 2 PO 4 ? What is the conjugate base of HCO 3 Identify the conjugate acid-base pairs in H IO 3 (aq) + 2 O 4 3 + H 2 C 2 O 4 Has one more H, and one more fewer minus charge than the base. Has one fewer H, and one more minus charge than the acid. Acid2 gave- P Base2- Accepted P Base1 accepted p Acid1 HCl/cl- conjugate acid base pairs NH3/NH4+ conjugate acid/ base pairs
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6/6/11 66 Chapter 18 Acid-Base Equilibria Example Problem : What is the conjugate acid of H 2 PO 4 ? What is the conjugate base of HCO 3 ? Example Problem : Identify the conjugate acid-base pairs in HIO 3 (aq) + HC 2 O 4 (aq) IO 3 (aq) + H 2 C 2 O 4 (aq) H2PO4- + H+--------- H3PO4 HCO3----------- CO32- + H+ acid 1 base2 Base 1 acid 2 HIO3/IO3- HC2O4-/ H2 C2 O 4
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6/6/11 77 Chapter 18 Acid-Base Equilibria The Conjugate Pairs in Some Acid-Base Reactions Base Acid + Acid Base + Conjugate Pair Conjugate Pair Reaction 4 H2PO4 - OH - + Reaction 5 H2SO4 N2H5 + + Reaction 6 HPO4 2- SO3 2- + Reaction 1 HF H2O + F - H3O + + Reaction 3 NH4 + CO3 2- + Reaction 2 HCOOH CN - + HCOO - HCN + NH3 HCO3 - + HPO4 2- H2O + HSO4 - N2H6 2 + + PO4 3- HSO3 - +
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6/6/11 88 Chapter 18 Acid-Base Equilibria Water - Acid or Base? Note the two acid-base reactions examined above: HCl(aq) + H 2 O( l ) H 3 O + (aq) + Cl - (aq) NH 3 (aq) +H 2 O( l ) NH 4 + (aq) +OH - (aq) Water is amphiprotic (amphoteric) : H 2 O( l ) + H 2 O( l ) H 3 O + (aq) + OH (aq) A substance that can act as either an acid o a base.
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6/6/11 99 H 2 O( l ) + H 2 O( l ) H 3 O + (aq) + OH (aq) Equilibrium constant expression: (***Pure liquids like H 2 O are omitted) K w = K w = ionization constant for w ater = 1.0 x 10
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Chapter+18 - Chemistry The Molecular Nature of Matter and...

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