Acids and Bases

Acids and Bases - Acids and Bases Chapter 14 Zumdahl...

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Acids and Bases Chapter 14 Zumdahl Arrhenius concept: Acids produce hydrogen ions in aqueous solution and bases produce hydroxide ions in aqueous solution. Brønsted-Lowry model: An acid is a proton (H + ) donor and a base is a proton acceptor. Hydronium ion: H 3 O + , is formed when water acts as a base. Equation for formation: HA (aq) + H 2 O (l) ↔ H 3 O + (aq) + A - (aq) Conjugate acid: what is left over after a base ionizes. Conjugate base: what is left over after an acid ionizes. The acid dissociation constant yields an equilibrium expression: [ ][ ] [ ] HA A O H K a - + = 3 . Often just say H + instead of H 3 O + , but need to remember that in water the H + ion will form hydronium. Can also have gaseous acid/base reactions: NH 3 (g) + HCl (g) ↔ NH 4 Cl (s) Acid strength: a strong acid is one where the equilibrium lies far to the right and yields a weak conjugate base; a weak acid is one where the equilibrium lies to the left and yields a strong conjugate base. 1
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Types of acids: oxyacids – the acidic proton is attached to oxygen; organic acids – have a carboxyl group C R O O H and are weak acids. Amphoteric: can act as either an acid or a base. Water is amphoteric. Autoionization: the transfer of a proton from one molecule to another of the same substance 2 H 2 O (l) ↔ H 3 O + (aq) + OH - (aq) The ion product constant for water is [ ][ ] 14 3 10 1 - - + × = = OH O H K w this is the relationship at 25 o C of any aqueous solution. pH scale: a convenient way to measure the amount of H + ion in solution. p of anything means to take the –log of it. pH = -log[H + ]; pOH = -log[OH - ], pK = -log(K). pH decreases as [H + ] increases. At 25 o C, pH + pOH = 14. Major species: solution components present in relatively large amounts. We can solve acid/base equilibrium problems the same as gas phase equilibrium problems from chapter 13. Steps to solving a weak acid equilibrium problem: 1. List the major species in the solution. 2. Choose the species that can produce H + , and write the balanced equation for the reactions producing H + . 2
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3. Using the value for the equilibrium constant for the reaction you have written, decide which equation will dominate in producing H + .
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This note was uploaded on 07/22/2008 for the course CHEM 105A taught by Professor Bau during the Summer '04 term at USC.

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Acids and Bases - Acids and Bases Chapter 14 Zumdahl...

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