acids and bases

acids and bases - 15-1 ACIDS AND BASESAcids: taste sour,...

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Unformatted text preview: 15-1 ACIDS AND BASESAcids: taste sour, e.g., vinegar and lemons (acetic and citric acids, respectively), and cause plant dyes to change color. Aqueous solutions of acids conduct electricity Bases: taste bitter and feel soapy (used in cleaners, and cause plant dyes to change color. Aqueous solutions of bases conduct electricity Arrhenius definitions(1884): acids increase [H+] while bases increase [OH-] in solution. Question:What is the difference between a strong and weak acid, or a strong and weak base? What is the problem with the Arrhenius definition and the characteristics of strong and weak acids and bases? (Hint, NH3is a base) Compare, through the following examples, the Arrhenius definition acids and bases with two others developed in the 1920s: the Brnsted-Lowryand the Lewisdefinitions. HCl(aq)+ NaOH(aq)H2O(l)+ NH3(aq)BF3(g)+ NH3(g)15-2 Brnsted-Lowry Acid Base TheoryReactions between Brnsted-Lowry acids and bases are proton transfer reactionsAn acid donates H+(a proton) and a base accepts H+A B-L base does not need to contain OH-Water can behave as either an acid or a base and is considered amphoteric- a substance that can behave as an acid or a base The portion of an acid remaining after a proton is donated is its conjugate baseSimilarly, the product formed after a base accepts a proton is its conjugate acidExample:Identify the acid, base, and conjugate acid and base HClO2+ H2O OCl+ H2O HCl + H2PO4NH3+ H2PO415-3 Lewis Acid Base TheoryProvides a more universal definition of acids and bases than the Brnsted-Lowry description Acid Base Can be used for solid and gas phase reactions as well as those in solution Lewis acids and bases do not need to contain protons (H+) or hydroxide (OH-) Lewis acids generally have an incomplete octet and are electron deficient (e.g.,BF3) Transition metal ions are generally Lewis acids Lewis acids must have a vacant orbital (into which the electron pairs can be donated) Is NaOH a Lewis base? Is NH3a Lewis base? 15-4 Example:Identify the Lewis acid and base for each and show the transfer of electrons: BF3+ FBF4SnCl4+ 2 ClSnCl62N2H4+ HNO3N2H5++ NO3 B(OH)3+ OHB(OH)4SO3+ H2O H2SO4Compounds with -bonds can act as Lewis acids: H2O(l)+ CO2(g)H2CO3(aq)Mechanism: 15-5 Strong Acids The most common strong acids are HCl, HBr, HI, HNO3, HClO3, HClO4, and H2SO4. Strong acids are strong electrolytes and ionize completely in solution (e.g....
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This note was uploaded on 04/10/2008 for the course CHEM 101 taught by Professor Kassel during the Spring '08 term at Villanova.

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acids and bases - 15-1 ACIDS AND BASESAcids: taste sour,...

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